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Potato Related Hort-Bytes

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potato thumbnailArticles are being published every day with information that can be used by Saskatchewan producers. The Hort-Bytes are a collection summaries of some of the most relevant articles recently published.


The article summaries are divided into sections based on content:

Within each section article summaries are organized alphabetically. Full citations are provided with each summary to allow for easy retrieval of orginal articles.

Click on the title to read the article summary:

A Couple of Suggestions on Managing Rhizoctonia

Rhizoctonia can negatively affect potato yields, as the stem lesions interfere with the movement of energy from the tops into the tubers and the movement of water from the roots into the tops. The presence of the resting spores (sclerotia) of Rhizoctonia on the harvested tubers also reduces their value in both the table and seed markets. Inoculum of Rhizoctonia may be present in the soil and also on the seed - but the relative importance of these two inoculum sources is still a matter of debate. Research out of Idaho suggests that the levels of Rhizoctonia on the seed were more important than soil inoculum levels as determinants of both the incidence of stem lesions and the intensity of scurf on the harvested crop. Conclusion : Clean seed is always a good investment. Research out of Michigan has again confirmed the importance of soil temperature at planting in determining losses to Rhizoctonia. While Rhizoctonia was severe in 8C soil, problems with stem canker and tuber scurf were minimal if planting was delayed until soil temperatures reached 14C. They found that seed treatments containing the fungicide flutolonil (ie; Maxim) reduced both stem canker and tuber scurf. Seed treatments were particularly valuable when the crop was planted into cool soil. Similar responses to Maxim seed treatments have been seen in Saskatchewan in research trials conducted by Dr. Jill Thomson.

Sources : Atkinson, Thornton and Miller (2006). Amer. J. Potato Res. 83: 97 (Abstr.)
Devan, Kirk, Wharton, Schafer and Pavani (2006). Amer. J Potato Res. 83: (Abstr.).
Thomson and Waterer (2006). Final Report for ADF Project No. 2002- 0172.

Alpine Russet

Alpine Russet (A9305-10)







Alpine Russet is a new russet type processing potato released by Tri-State Potato Variety Development Program (PVMI).  Alpine plants are moderate sized with an upright canopy.    Alpine is slow to mature but produces higher total and marketable yields than either Burbank or Ranger.   Tubers are uniform shaped with an intermediate specific gravity.  Alpine shows exceptional processing quality, especially out of cold storage.   Disease resistance is generally equivalent to Burbank although it appears to be susceptible to PVY infection.  In trials conducted in 2010 in Saskatchewan, Alpine showed less Late Blight damage to the foliage than either Ranger or Burbank.   Alpine produces equivalent yields with less irrigation and N fertility than the standard russet varieties. 

The University of Saskatchewan, in conjunction with the Saskatchewan Seed Potato Growers Association, is evaluating Alpine Russet for its suitability for prairie production conditions.  For the 2010 trial results see:

Source: J.L. Whitworth et al. (2011).  Amer. J. Potato Res.  88: 256-268       

Black Dot ... Another Disease to Look Out For?

Since beauty is in the eye of the beholder, how a potato looks is a critical aspect of its market value. A wide range of diseases, including Rhizoctonia, silver scurf, common and powdery scab can blemish the surface of potato tubers. Although these blemishes have little impact on the actual quality of the infected tuber, they reduce its eye appeal and its market value. Recently, growers in north-central United States and Manitoba have noticed the emergence of another threat to the beauty of their crop - black dot (Colletotrichum coccodes). Tuber symptoms of this fungal disease are similar to and easily confused with the symptoms of silver scurf (Helminthosporium solani). Black dot causes smooth, silvery brown lesions on the surface of the tubers. Lesions present at harvest continue to grow as the potatoes are stored. The lesions are speckled with very small black dots which are the reproductive structures of this disease. Although tuber damage by black dot is usually just cosmetic, the lesions allow water loss from the tubers. Unlike most of the other cosmetic pathogens of potatoes, black dot attacks both the above and below ground portions of the plant - particularly if the plant has been weakened by poor water or fertility management or environmental stress. Black dot produces small, water-soaked lesions on the leaves. These lesions rapidly turn black but don’t appear to grow much after the initial infection. Extremely severe infestations will cause general yellowing and wilting of the foliage - symptoms that are easily confused with other wilt-causing problems like Fusarium and Verticillium.

Black dot moves from region to region and field to field via infested seed. At present, black dot levels on seed are not specifically regulated. Little is known about the efficacy of fungicidal seed treatments for the control of seed-borne black dot - but the fact that this disease is fairly widespread suggests that standard seed treatment do not provide a high degree of control. Once a field is infested with black dot, the problem becomes persistent - but levels of black dot can be managed. Long crop rotations appear to reduce but not eliminate soil infestations with black dot. All commonly grown varieties of potatoes appear somewhat sensitive to black dot - but the earlier maturing, thin-skinned red and white types are more susceptible than the russet types. The black dot lesions are also more obvious on the skins of red and white potatoes than on russets. Foliar fungicides commonly used to control early and late blight also protect the foliage against black dot - but they do not protect the tubers. The longer the tubers are left in the ground after the tops have died, the higher the incidence and severity of black dot. The conditions that promote rapid curing of a freshly harvested crop (humid @ 15C) are also ideal for the development of the disease. Growers with black dot problems should keep the curing period to a minimum and consider reducing humidity levels in the curing area. Long term storage under warm humid conditions allows black dot lesions to continue developing - this is why damage by black dot appears to be more of a problem in processing and table potatoes than in seed. The potential for black dot to develop in the retail handling chain is not well known - however the relatively warm and moist conditions that occur when table potatoes are washed, packed into cellophane bags and then displayed on the supermarket shelf are near ideal for the development of black dot.

Primary source: Lees and Hilton (2003). Plant Pathology 52: 3-12.

For more information on Black Dot research being conducted by the University of Saskatchewan ... contact Dr. Doug Waterer or Dr. Jill Thomson.

Border Treatments to Reduce Insecticide Use in Seed Potatoes

Use of border trap crops, like newly planted cereals, is a proven tool for reducing Potato Virus Y (PVY) infection of seed potatoes. The winged aphids that transmit PVY from field to field appear to prefer to initially land on the border crops before moving into the seed potato field. The aphids will probe the non-host border crop a few times before moving on - and any PVY particles present on their feeding parts are left on the non-host cereal crops where they die. Border strips of cereal crops will not protect seed potatoes from infection aphid transmitted persistent viruses like Potato Leaf Roll (PLRV) - however, they may still be useful in management of this virus threat. Carroll et al (2009) showed that aphid populations in the cereal crop borders and the first few rows of the potato crop were up to 27X higher that in the centre of the field. Surveys of seed potatoes fields in Saskatchewan conducted by the SSPGA from 2006-2008 also found aphids tended to cluster at the edges of fields. Carroll found that by treating the heavily populated field edges with insecticides they could control the spread of aphids from the field margins throughout the field while using only a fraction of the insecticides required to treat the entire field - thereby reducing costs and environmental impact of the spray treatment. As the aphid population in the field margins was replenished within 7 days of insecticide treatment, they suggested that more frequent treatment of the field margins might provide a higher level of disease control than less frequent treatment of the entire field.

Sources: Carroll et al (2009). Amer. J. Potato Res. 86: 31-37.
SSPGA - Pesticide Reduction Program (2006-2008).

Consumer Acceptance of GM - Potatoes ... About a Decade Away

Based on the rate at which consumers picked up other novel concepts like microwave ovens, diet soft drinks and frozen food, Joe Guenthner, a potato marketing authority at the University of Idaho, predicts that it will be another 5-10 years before the average North American consumer will be ready to embrace genetically modified (GM) food products like the New Leaf potato. However, once the consumers’ characteristic resistance to anything “new” is overcome, acceptance is typically quite rapid, reaching 80% of peak demand within a decade. The speed at which GM products will be accepted could be greatly accelerated if GM products are developed that obviously benefit the consumer ... ie; potatoes with fewer calories or superior flavor. Many of these so-called “second generation” GM products are already in development.

Source : J. Guenthner, 2002. Amer. J. Potato Res. 79: 309-316.

Cover Crops of Limited Value for Erosion Protection in Western Canadian Potato Fields

Potato top killing and harvesting procedures leave the preferred light soils open to wind aand water erosion, both in the fall after the crop is harvested and again in the spring. Planting a cover crop like a cereal after the potatoes are harvested may protect the soil from erosion while also protecting soil nutrients from leaching and potentially suppressing weed growth. One of the major challenges in cover cropping is getting adequate growth of the cover crop during the limited time period available between when the potato crop is harvested and freeze up. Moyer and Blackshaw have evaluated the performance of several types of cover crop (oat, barley, winter triticale and fall rye) seeded after a potato crop was harvested (early October) in trials conducted in the potato production zone of Alberta. None of the cover crops produced enough growth before fall freeze up to protect the soil against erosion over the winter. As the fall rye and winter triticale survived the winter, these cover crops went on the produce enough ground cover to protect the fields against erosion prior to planting in the next spring. However, both the rye and triticale cover crops reduced growth and yields of wheat crops planted into the fields, even though the cover crops were killed down with glyphosate. They suggested that cover crops might be of more use in situations where potatoes are harvested earlier in the season (ie; table or seed potatoes), leaving a longer period available for establishment of the cover crop prior to fall freeze up. In Saskatchewan several growers have achieved a good level of protection by spreading straw on erosion prone areas of their recently harvested potato fields.

Source : Moyer and Blackshaw (2009). Can. J. Plant Sci 89: 133-139.

Cut Seed versus Whole - the Verdict is Still Out

In a study comparing whole versus cut seed of Russet Burbank, University of Idaho researchers found little difference in the overall performance of the seed - as long as the cut seed was also treated with a fungicide. For example, whole seed was more resistant to seed piece decay by dry rot than cut seed - unless the cut seed was also treated with an effective fungicide. Fludioxonil (Maxim) and Mancozeb (Potato Seed Treatment) provided better control of dry rot of cut seed than did a thiophanate-methyl based product (ie; Senator). All the fungicidal treatments tested on the cut seed reduced the incidence of Rhizoctonia stem canker relative to the untreated whole seed. The effect of seed form (whole versus treated cut) on time to emergence, stand %, crop vigor and ultimately crop yields varied from year to year - reflecting differences in seed quality and growing conditions. In general, whole seed performed as well as cut seed treated with a fungicide - although the average tuber size in the crop grown from whole seed was slightly smaller than when cut seed was used. Although whole seed performed well - it may still benefit from the application of a fungicidal seed treatment - particularly in situations where Rhizoctonia is a common problem. The researchers speculate that greater differences in seed performance could be expected under less favorable field conditions, or when cultivars prone to seed decay (ie; Yukon Gold) or with limited number of tubers set (ie; Shepody) are used.

Source : Nolte, Bertram, Bateman and McIntosh (2003). Amer. J. Potato Res. 80:1-8.

Dakota JewelDakata Jewel (ND 3196-1R) - A New Red-Skinned Table Potato

Dakota Jewel is a 2004 release by the North Dakota Potato Breeding program that may also be of interest to Saskatchewan growers of seed and table potatoes. This red-skinned oval table potato combines the attributes of Red LaSoda, Bison, Chieftain and Norchief in its pedigree. Dakota Jewel produces a vigorous upright plants that mature about 2 weeks after Norland. Total yields of Dakota Jewel are similar to Norland under both dryland and irrigated conditions - but its pack should be enhanced by its superior color and uniformity of tuber size and shape. It has a good number of eyes that tend are fairly uniformly distributed around the tuber. Specific gravities of Dakota Jewel are higher than standard table reds - this results in a slightly drier texture but good flavor. Dakota Jewel shows good skin set after desiccation and most importantly, its skin color holds during storage. It also has an exceptionally long dormancy period. In most situations, this will be advantageous - except that emergence may be erratic if seed is planted direct out of cold storage. Dakota Rose is similar to Norland in its sensitivity to diseases - although it may have some enhanced resistance to powdery scab. Other potential concerns about Dakota Jewel are some isolated problems with hollow heart and its sensitivity to metribuzin.

Dakota RoseDakata Rose (ND 3574-5R) - A New Red-Skinned Table Potato

Since being released by the North Dakota Potato Breeding program in the late 1990's, Dakota Rose has rapidly gained popularity in North Dakota and Minnesota and it may also be of interest to Saskatchewan growers. This red-skinned oval table potato combines the superior red color and color retention characteristics of NorDonna with the yield and earliness characteristics of Norchief and other varieties out of the North Dakota program. Dakota Rose produces a vigorous upright plant with distinct dark purplish-green foliage. Total yields of Dakota Rose are similar to Norland and Pontiac under both dryland and irrigated conditions - but it consistently produces a superior pack out as it has few internal or external flaws. Tubers of Dakota Rose are quite uniform in size and shape with a good number of uniformly spaced eyes. It compares favorably with standard table varieties for flavor, but is superior in skin color, especially after storage. Dakota Rose is similar to Norland in its sensitivity to diseases. The major concern expressed about Dakota Rose is its slowness to set a skin - 3 weeks from top-kill to harvest are recommended. In trials conducted by the University of Saskatchewan in 2006, Dakota Rose appeared slower to die down than Norland, but it was much easier to handle at harvest than traditional late-season varieties like Pontiac or Sangre.

Does Early Blight get Tougher to Control as the Season Progresses ?

Growers relying on repeated application of certain protectant fungicides to prevent Late Blight (Phytophthora infestans) may accidently be increasing their risk of attack by Early Blight (Alternaria sp). Growers in N. Dakota have been noting increasingly severe outbreaks of early blight in fields regularly sprayed with fungicides that were supposed to control both Late and Early blight. Staff at North Dakota State University found that the dosage of the commonly used fungicide chlorothalonil (Bravo) required to kill Early Blight spores tended to increase in at least some N. Dakota fields as the growing season progressed. These growers were typically applying the chlorothalonil on a 5 to 7 day basis as part of a standard Late Blight control program. It appears that repeated application of this one product was selecting for resistant strains of Early Blight - and these strains consequently tended to take over the fields as the season progressed. Fortunately, fungicide resistance levels in the Early Blight population rapidly returned to normal once the growers ceased spraying or if they alternated blight control products ie; Bravo followed by Dithane or Headline/Quadris. These results emphasize the importance of considering resistance management when developing your pest control programs.

Source : Holm, Rivera, Secor and Gudmestad (2003). Amer. J. Potato Res. 80: 33-40.

Don’t Give Late Blight a Place to Hide

Cull piles represent a potential source of Late Blight if blight-infected potatoes in the pile manage to avoid being frozen and begin to sprout the next spring. A study conducted in Michigan showed that culls buried deep in the pile had the greatest chance of avoiding frost through the duration of the winter. The deeper the pile, the greater the odds that some areas of it would be frost-free through the winter. Not surprisingly, the numbers of potatoes successfully surviving the winter increased in warm years or if an insulating layer of snow kept the cull pile warm. Although Saskatchewan winters are considerably longer and colder that in Michigan - this study still demonstrates the wisdom of keeping cull piles small and spreading the piles as frequently as possible.

Source - Kirk (2003). Amer J. Potato Res. 80:145-149.

Early Hilling is Best

In a study that compared power versus disk hillers, Konschuh and Dalpe found that hilling at or soon after emergence resulted in the best yields and fry quality of Russet Burbank potatoes in Alberta, irrespective of the type of hiller used. Once the plants were more than 7" tall, the power hiller began to cause enough damage that yields were significantly reduced. The disk hiller caused less damage than the power hiller at more advanced crop stages.

Source : Konshuh and Dalpe (2004). Abstr. 88th PAA meeting. p. 74.

Evaluating Application Options for Blight Sprays

In Washington State, 75% of the fungicides used for Late Blight control are applied from the air, while the remainder of the acres are treated by mixing the fungicide into the irrigation water and then applying the mixture through the pivot system (chemigation). Ground rigs are considered too slow and costly. Geary and associates have recently examined the relative strengths and limitations of both methods of fungicide application using a range of late blight control products . Their main findings are;

  1. Aerial applications provide good coverage, if the spray program commences prior to canopy closure. If however, the onset of the aerial spray program is delayed until after canopy closure, coverage of the lower layers of the canopy will be inadequate ... unless the sprays are repeated and the fungicides are relocated within the canopy by rain and/or irrigation.
  2. Increasing the volume of water used in an aerial application program from 5 gal/a to 10 gal/a did not improve the quality of coverage or disease control ... but did substantially increase the cost of delivering the spray. Addition of spreaders or stickers to the mix was also ineffective at improving canopy penetration for aerial-applied products.
  3. Although the fungicides tested in the aerial application trials varied greatly in cost, they all provided an acceptable degree of late blight control ... if the spray program was initiated prior to canopy closure and repeated at 10 day intervals. EDBC products like polyram and dithane represented the lowest cost control options in this trial.
  4. Quality of coverage was never a problem in the chemigation program ... the major limitation of that method of application was excessive dilution of the fungicide. In a typical chemigation program, the fungicide is mixed into the 5,000 gallons of water needed to irrigate an acre of land (1/3 inch). One option is to apply the fungicide through a low volume boom installed on the pivot .. but this type of modification is costly. Another option is to increase the speed of the pivot system when applying fungicide. They however found little improvement in the amount of fungicide recovered from the crop even when the pivots were run at top speed (delivering ca 1500 gal/a).
  5. Uniformity of coverage did not differ for the various products tested in the chemigation trials. However, chemigation programs based on Curzate were not as effective as the other programs tested. They suggested this was due to warm temperatures (> 24C) following application.

Source : Geary, Hamm and Johnson (2004). Amer. J. Potato Res. 81: 305-315.

Evaluation of Fungicides for Control of Late Blight

Daayf and Platt compared the efficacy of six registered fungicides for control of growth and spore formation by two strains of A2 Phytophthora infestans, the fungus that causes Late Blight. At a set rate of application, Bravo and Acrobat provided the best overall control of both growth and spore production by the Late Blight fungus. Ridomil was relatively ineffective, particularly against the U.S. 11 strain of Late Blight. By contrast, Acrobat and Dithane were highly effective against U.S. 11 and might be recommended in regions such as B.C. where this strain of Blight is prevalent. The researchers emphasize that their studies were conducted using pure cultures of the Late Blight fungus under laboratory conditions - and consequently the results are not necessarily an accurate indication of how well these fungicides will perform in the field.

Source: Daayf and Platt (2002). Amer. J. Potato Res. 79.

Everything You Ever Wanted to Know About Aphids ....

Some of the key points raised by Radcliffe and Ragsdale in their recently published comprehensive review of the biology of aphids and the viral diseases they spread are that .... .

- Green peach aphids which can spread both Potato Leaf Roll Virus (PLRV) and Potato Mosaics (PVY) feed and multiply on over 800 different plant species, including many of the crops commonly grown in Saskatchewan. Canola is particularly attractive for aphids and also represents an excellent food source leading to rapid growth in aphid numbers. As the canola matures, the aphids move to adjacent later maturing crops such as potatoes.

- Pea, buckthorn, potato and cereal aphids are far less efficient at spreading PLRV and PVY than the Green Peach Aphid, but where extremely high populations of these alternate vectors are common, they may make a significant contribution to the spread of viral diseases of potatoes.

- The minimum isolation distance recommended to protect seed potato fields from virus-infected commercial fields is 5 km for PVY and 30 km for PLRV. The greater isolation area required for PLRV reflects the fact that aphids which have fed on plants infected with PLRV continue to spread the virus for the remainder of their lifespan.

- Insecticides are of limited utility for protecting crops against the aphids that carry PVY and PLRV. In most cases, the insecticides do not work fast enough to kill the aphids before they have had a chance to feed at least briefly on the crop. It only takes a few seconds of feeding for the viruses to be transmitted from their aphid vectors into the potato crop. Mineral oils applied to the foliage appear to be a more effective disease prevention option, as they actively deter aphid feeding. However, mineral oils are only effective for short periods and must be repeatedly re-applied. Complete coverage, deep into the canopy is required for effective aphid management with any foliar-applied aphid control product.

- Aphids are attracted to crops based on their color, but fallow areas at the edge of the crop are also attractive to many species of aphid. Consequently, the first few rows of the field are usually the most heavily colonized by aphids and are therefore at the greatest risk of infection by PVY and PLRV. Growers should be especially vigilant when roguing these rows and if disease pressures are high should consider segregating out the tubers harvested from the field margins. Growers should avoid using fallow areas to segregate small plots of early generation material and should instead plant the border areas down to winter wheat.

- Tuber yields are rarely reduced by recent (in-season or primary) infection by PLRV. Primary infections with PLRV only lead to net necrosis in a few, particularly sensitive cultivars like Russet Burbank. Primary infection by PVY reduces yields by reducing the average tuber size. Tablestock growers who save unmarketable small tubers for use as seed may inadvertently be creating seed lots with high levels of PVY.

- As potato plants mature in the fall, the rate at which viruses picked up in the tops are transferred to the tubers begins to slow. This explains why rapid and thorough top kill helps reduce the movement of viruses from the tops into the tubers. Potato varieties also differ in the efficiency of transmission of viruses from the tops to the tubers ... this explains why the extent of virus contamination can differ for varieties grown side by side in a contaminated field.

- Yield losses arising from planting virus infected seed (secondary infection) are generally much higher than losses due to primary infection. However, the actual yield losses from planting infected seed are often mitigated by the phenomenum of yield compensation. Since the plants arising from virus-infected seed tend to small and weak, this leaves more growing room for adjacent healthy plants which produce correspondingly higher yields. This partially compensates for the poor yields produced by the virus-infected plants.

Source : Radcliffe and Ragsdale (2002). Amer. J. Potato Res. 79: 353-386.

Factors Influences Purchasing Decisions for Table Potatoes

In a survey of “typical” supermarket shoppers in Maine, Jemison and co-workers found that skin and quality and place of origin were the most important factors influencing the decision to purchase fresh market or table potatoes. Consumers were consistently looking for a bright, blemish-free skin. Flesh color was also important, but the preferred flesh color (white, cream , yellow or other) was a matter of personal preference. Of the red varieties examined in their survey, Norland was rated as having the most appealing skin quality and overall tuber appearance. The survey participant responded very positively to the concept of “locally grown” potatoes. Price and method of crop production (organic vs conventional) were relatively unimportant to most consumers, but for a small proportion of the population these factors were the most important in determining their purchase intentions. On average, the survey participants consumed fresh market potatoes (boiled, baked, mashed, roasted) about 2-3 times per week. Although the survey participants were generally aware that potato prepared in this manner represented a healthy food choice, a significant proportion of the participants were interested in reducing their overall carbohydrate intake - potatoes may be vulnerable to this type of dietary restriction. Younger consumers showed a preference for mashed potatoes, whereas roast/baked potatoes were preferred by the more mature consumers.

Source : J. Jamison, P. Sexton and M. Camire (2008). Amer. J. Potato Res. 85: 140-149

Frozen Potato Management

By Dr. Doug Waterer, University of Saskatchewan

A cold and cloudy summer that delayed crop development, followed by rain delays in September has Prairie potato growers concerned about getting the 2004 potato crop out of the ground ahead of the frost. Symptoms of cold damage to potatoes vary with the severity and duration of the low temperature event. Potato tubers exposed for short periods to temperatures slightly below the freezing point may experience no obvious injury - particularly if they are allowed to thaw prior to handling. Nonetheless, these potatoes may have suffered chilling injury. Chilled potatoes appear sound and store well, but their performance as seed is impaired. Chilled seed potatoes are slow and uneven to sprout and are very sensitive to seed piece decay. As the duration or intensity of freezing temperatures increases, obvious symptoms of tuber damage become apparent. Frost damage initially shows up as a light reddish brown discoloration of the flesh, often on the side or end of the tuber closest to the soil surface. The stem end of the tuber and the vascular ring are also good places to look for freezing damage. Once the frozen tissues thaw, the damaged areas collapse, leading to the classic wet areas on the tuber surface. This surface moisture is ideal for the development of soft rot bacteria which spread from the frozen tubers onto adjacent healthy tubers. In this way, entire bins can be lost to relatively minor levels of frost damage.


Frost Prevention

Obviously, early harvest represents the best tool for frost prevention. The risk of frost damage increases as temperatures decline and the exposure period increases. Short-term exposure to temperatures well below 0 degrees C will not result in significant frost damage if the soil goes into the frost event warm. As the fall progresses, the potential for significant rewarming of the soil during the day declines - meaning a frost event that caused little damage early in the season may cause more severe damage later in the fall. Soil is a good insulator – that explains why adequate hilling represents the second line of defence in frost management. The insulating capacity of the soil increases with porosity - silt soils are better insulated than sandy soils. Similarly, dry soils are at risk during even minor frosts. Green tubers should be culled out prior to storage, as tubers close to the soil surface are at increased risk of frost damage. Similarly, small immature tubers are more easily frozen than mature tubers. Varieties that produce large tubers that set high in the hill are also at increased risk of frost damage.


Management of Frozen Potatoes

The management regime used to handle frozen potatoes depends on prompt and accurate assessment of the extent of damage. Once the tuber thaws, symptoms of frost damage take 24-48 hours to develop. Ideally harvest is delayed for a couple of days after a frost to allow obvious symptoms to appear and appropriate management decisions to be developed. Low levels of damage may be graded out on the harvester or the conveyor line. Look for tubers with soil adhering to the leaking, frost damaged areas. If more than a few percent of the tubers going into the storage are frozen, it may be advisable to skip the curing step as soft rot bacteria will run wild at the warmer temperatures required for wound healing. Unfortunately, skipping the curing period leaves the crop open to increased moisture loss and disease during the subsequent storage period. Turning off the bin humidifier and increasing air flow through the pile will help carry away the moisture leaking from frozen potatoes but this also accelerates dehydration of the undamaged tubers. Once damage due to frost, late blight, leak or other rot causing disorders exceeds 5% of the crop, the odds of successful long term storage are poor and other marketing options should be investigated. Growers should monitor suspect lots frequently as frost damage may not show up until several weeks after harvest.

Fungicide Efficacy Varies Depending on Strain of Late Blight

Daayf and Platt (2003) used a leaf assay test to demonstrate that the relative efficacy of commonly employed foliar fungicides varies depending on the strain of Late Blight encountered. They found that Tattoo C and Bravo were effective at preventing both the US 8 and US 11 strains of Late Blight presently prevalent in North America. Acrobat, Dithane and Curzate worked well against US 8 but were less effective against US 11. Ridomil Gold was ineffective against either strain.

Source : Daayf and Platt (2003). Amer. J. Potato Res. 80: 329-334.

Good Flavor ... and Good for You

Potatoes are known as a good source of food-energy, high quality protein and significant amounts of essential vitamins and minerals. Less well known is their value as source of dietary antioxidants (flavenoids and carotenoids). Antioxidants are the latest “hot” topic in health, with diets rich in antioxidants linked to reduced risk of certain cancers and heart disease as well as improved eye health. Levels of antioxidants in potatoes are much more strongly influenced by genetics (variety) than by growing conditions or management practices. Varieties with colored skin and/or flesh have much higher antioxidant value that white skinned/fleshed types. Purple skin/purple flesh types have highest antioxidant levels followed by red then yellow. Antioxidants levels in Russet Norkotah are much high than other white fleshed types. Although the impact of handling and cooking practices on antioxidant levels is still largely unknown- there are some indicators of their importance. Levels of Vitamin C (another important antioxidant) in potato decline by 45% over the storage period - with the rate of decline accelerating if the potatoes are stored at high temperatures or are damaged prior to storage. Boiling potatoes in their skin caused the least loss of Vitamin C content (45%) during cooking. Blanching prior to frying resulted in the loss of 60-70% of the Vitamin C content while dehydration effectively destroyed all the Vitamin C in the potato.

Source : Brown (2005). Amer. J. Potato Res. 82: 163-172.

Identifying the Real Villain when Mosaics Strike

In many areas, the arrival of the Green Peach Aphid (GPA) is regarded as the onset of the danger period for transmission of viral diseases such as PVY. However, occasional problems with mosaics (PVY) in areas where GPA are rare have led researchers to review the relative importance of other aphid species as vectors of this viral disease. The GPA is known to be a highly efficient vector for PVY, and it shows a strong preference for potatoes as a food source. By contrast, other species of aphid may be relatively poor at spreading the virus or they may avoid feeding on potatoes ... but if they are present in high enough numbers, they may represent an important alternative method for spread of PVY. In Idaho, Halbert and associates found that a species of aphid that normally feeds on Russian olive trees and Canada Thistle was the most important vector of PVY. Although this aphid is relatively ineffective at spreading the disease, it is present in such large numbers that it eventually makes a significant contribution to disease movement into non-preferred host crops such as potato. For the same reason, several cereal aphids were also important - whereas the GPA was relatively unimportant, simply because it was rare in that area. The aphid monitoring program conducted by Andrew Sullivan has demonstrated that the GPA is also relatively rare in Saskatchewan ... but that the local fields do host fairly large numbers of other aphid species. Although they may be less efficient vectors of disease, growers cannot afford to become complacent regarding the potential for these aphids to expand a minor problem with PVY into a full-blown outbreak. The old saying - Start Clean to Stay Clean - is still good advise.

Source - Halbert, Corsini and Wiebe (2003). Amer. J. Potato Res. 80:87-91.

Impact of Glyphosate Drift on Yield Potential of Potato

Potatoes are commonly exposed to accidental drift from nearby application of non-selective systemic herbicides like glyphosate (Roundup, Rustler, Touchdown etc). Exposure can occur early in the growing season as a function of spraying to control weeds on fallow land and in herbicide resistant crops (e; canola). Later in the year these products are used for pre-harvest desiccation of pulses, oilseeds and cereal crops. Researchers at North Dakoa State University have studied the impact of simulated glyphosate drift on the yields and crop quality of Russet Burbank potatoes. As expected, they found that the degree of crop damage increased with the dosage of glyphosate absorbed by the potato crop. In general, the earlier the exposure the greater the reduction in yields associated with exposure to herbicide drift ie; hooking stages > tuber set > tuber bulking). Yield loss was primarily due to a reduction in tuber biomass rather than any increase in cullage rates. As glyphosate impairs growth of both roots and shoots this loss of productivity would be expected. In addition to the immediate yield loss, exposure of a seed potato crop to glyphosate can severely impair the performance of seed in the next growing season. As this type of damage is difficult to detect prior to planting, extensive off-season grow-out trials are suggested if a grower suspects their seed potato crop has been exposed to glyphosate drift.

Source : Hatterman-Valenti and Auwater (2009). HortScience 44 p.1076.

Introducing Blazer Russet (A8893-1)

This recent release from the UDA-ARS Potato Improvement Program for the North Western United States is generating considerable interest amongst growers looking for a more easily managed, earlier maturing alternative to Russet Burbank for both fresh markets and processing. Blazer Russet produces a small upright plant with a moderate set of uniform-shaped, smooth, lightly russeted tubers. In trials conducted throughout the United States, yields of Blazer were equivalent to Russet Burbank in regions with a short growing season but lagged behind Burbank and Ranger in areas with a longer season. The main strength of Blazer is its superior tuber appearance – it produces a much higher % of tubers packing out as #1’s than other cultivars, making it a strong alternative to Burbank in the fresh market. The processing characteristics of Blazer are also excellent – with specific gravities and processing colors similar to Russet Burbank. Blazer is resistant to sugar ends and other forms of heat stress but is moderately susceptible to hollow heart.

Blazer appears to be exceptionally resistant to both common and powdery scab, is moderately susceptible to PVY and PLRV, but appears to be quite susceptible to early blight. Tubers are also susceptible to bacterial soft rot and fusarium dry rot and growers may need to take some extra care in seed selection and preparation for planting. Blazer has good expression of foliar and tuber symptoms of infection by bacterial ring rot.

Relatively little work has been conducted as yet on the agronomic requirements of Blazer. Because of the sensitivity of the seed to rot issues, the crop should be planted at the correct depth into relatively warm soil. Fertility requirements are anticipated to be equivalent to or slightly lower than Burbank. Blazer appears to tolerate post-emergence application of metribuzin. Blazer stores well at standard temperatures, however it breaks dormancy 40-50 days earlier than Burbank.

In trials conducted in Saskatoon in 2007 Blazer had higher yields than Shepody or Burbank at both 90 and 120 days. Fry colors for Blazer were superior to the standard cultivars at both harvests, but its chip colors were inferior to Shepody.

Source : Stark et al (2007). Amer. J. Potato Res. 84: 447-457.

Irrigation for Maximum Water Use Efficiency

Growers who rely on limited water sources such as dugouts need to consider how best to utilize the water available to them. Stark and his co-workers in Idaho found that keeping the crop well watered through tuber set, then gradually decreasing irrigation through to maturity provided the best yields with the least water. Towards the end of the season they were only replacing 50% of the total amount of water being used each week by the crop. GemStar Russet and Russet Norkotah were fairly tolerant of drought stress at all stages of growth, while Russet Burbank was far more drought sensitive.

Source : Stark, Love, Salaiz and Watt (2004). Abstr. 88th PAA meeting. p 58.

Linkage Between Rotation Crops and Problems with Powdery Scab

Powdery scab is becoming an increasingly common problem in potatoes worldwide - and unfortunately Saskatchewan fields are not immune to the problem. Powdery scab is a persistent soil borne disease - even intervals of 5 years between potato crops are not enough to eradicate the problem. However, the shorter rotations being adopted in many production areas appear to be exacerbating the problem. To make matters worse, research by Christ and others suggests that some of the crops commonly employed in potato rotations may actually serve as other hosts to the powdery scab organism - leading to a further build up in the field populations of this pathogen. They found that powdery scab could infect, feed upon and reproduce in the roots of oat, barley, and canola. Unfortunately all three of these crops are commonly included in potato rotations in Saskatchewan. Tomatoes and other members of the Solanaceae family were also excellent alternate hosts - an issue of importance if powdery scab makes its way into a garden situation. Wheat did not appear to be a suitable host. Rye and weeds like pigweed and lambsquarters appeared to trigger germination of the resting spores of the common scab, but their roots did not support subsequent infection or reproduction by the scab organisms. As a consequence, soil inoculum levels of powdery scab might be expected to decline following these plants. Although the market value of rye (or pigweed) is limited, the issue of the impact of rotation crops on powdery scab problems clearly merits further examination.

Source : Xu and Christ (2006). Amer. J. Potato Res. 83: 343-348.

More Information on Seed Piece Spacing

In a survey of 70 potato fields conducted in Washington State during 2000-2002, Pavek and Thornton found that the average in-row seed piece spacing was out by 25% relative to the target spacing. The best field surveyed was within 8% of the target spacing, while the worst was out by 67%. On average, a 92% stand was achieved, with planter failure causing more misses (6%) than seed piece rots (1%) or blind pieces (1%). The survey indicated that the quality of seed being planted in Washington today is far better than in 1970 - when nearly 20% of all misses were attributed to seed quality problems. About 4% of all hills contained more than one seed piece. Excessive planting speed, improper planter set up and maintenance were the most common causes of uneven seed spacing - but use of improperly sized, non-uniform seed lots was a contributing factor. Although most studies indicate that potato yields are seldom affected by uneven spacing - the average tuber size and the uniformity of tuber size distribution are very sensitive to irregularities in spacing. This size variability is becoming a real marketing issue in all potato sectors.

Source : Pavek and Thornton (2005). Amer. J. Potato Res. 82: 463-469.

More Reasons to Strive for a Good Uniform Stand

A perfect stand of uniformly spaced plants is a great objective at planting time; but Pavek and Thornton (2006) found that what was actually going on in growers= fields surveyed in Washington was far from perfection. On average, 7% of the intended plant population was missing; 6% of the misses were due to planter skips, while the remaining 1% was lost due to seed piece failure. Fortunately, this number of misses did not lead to a corresponding yield loss, as plants adjacent to the miss compensated for a portion (up to 70%) of the yield lost due to the missing seed pieces. Contrary to popular opinion, plants in adjacent rows did not benefit from the increase in available growing space created by the missing seed pieces. Irregular in-row spacing due to misses and general planter inaccuracy can also influence both tuber uniformity and quality. The more uneven the spacing, the more varied the tuber size distribution and the more frequently problems like hollow heart, greening and growth cracks will occur. Recent research out of Idaho shows that the negative effects of irregular spacing on yields and quality were much greater in situations where potatoes were widely spaced (40 cm (16") versus 20 cm (8")). Pavek and Thornton estimated that losses in yields and crop uniformity associated with erratic seed piece spacing, misses and doubles amounted to $10,000-13,000 for a typical 1/4 section pivot of processing potatoes in Washington. Losses of that magnitude re-enforce the importance of planting good quality seed using a well-maintained and adjusted planter operated at the proper speed.

Sources : Pavek and Thornton (2006). Amer. J. Potato Res. 83: 55-66.
Bohl, Love and Salaize (2006). Amer J. Potato Res. 83: 98 (Abstr.)

More Warm Weather on the Way ?

After another hot, dry summer in both North America and Europe, research by Hijmans (2003) examining the impact of global warming on potato production seems particularly timely . Although there are no guarantees as to the nature or extent of climate change we can anticipate within the next few decades, the “best guess” models come up with some interesting predictions and useful recommendations. If growing season temperatures increase by as little as 1.5oC on a worldwide basis, average potato yields are predicted to decrease by 10-20%. Severe yield reductions are predicted in areas that are already warm ... as any further increase in temperature will adversely affect both tuber set and bulking of the potato crop. However, the impact of global warming may be reduced in these areas if the growers can use irrigation for crop cooling or if they can shift the planting season to a cooler time. By contrast, areas like the Canadian Prairies, Scandinavia and Siberia may actually see an increase in yields as a function of a longer, warmer growing seasons. However, increased problems with disease and insect pests can be anticipated if the Prairie growing season gets longer and the winter period shorter. Storage of the crop also becomes more of a challenge as temperatures rise. The predicted rate of climate change is slow ... which should give the industry enough time to work out solutions to the anticipated problems. Breeding potatoes for increased heat stress tolerance is an obvious longterm approach. Re-direction of industry development into regions where climate change may actually be favorable would also seem like a sound longterm strategy.

Source : Hijmans (2003). Amer. J. Potato Res. 80: 271-280.

New Potato Cultivars of Limited Value in Manitoba

Production of potatoes in Manitoba has quadrupled over the past 25 years (1980-2006). While most of this increase is due to expanded production area, yields have also increased by almost 70%. In a study of the factors influencing productivity of the Manitoba potato industry, Carew et al. (2009) found that increased fertilize inputs combined with favourable growing conditions played a greater role in the observed increase in yields than did the adoption of new cultivars. Although a large number of new processing cultivars have been released by breeders at Agriculture Canada and elsewhere, adoption of these cultivars by the potato industry in Manitoba has been limited. This likely reflects the processors’ concerns about the uniformity and predictability of the processing quality of the new cultivars. While increased rates of application of fertilizer N were found to be enhancing potato yields in Manitoba, the yield response to P, K or S fertilizer and to irrigation was inconsistent.

Source : Carew, Khakbazan and Mohr (2009). Amer. J. Potato Res. 86: 442-455.

New Potato Varieties Worth $ 100 Million per Year to Pacific Northwest

Research indicates that the new varieties “Umatilla” and “Ranger Russet” pumped about $ 100 million in extra profits into the potato sector of the Pacific Northwest (PNW) in 2000. This increase in profits was attributed to the varieties producing superior marketable yields with fewer inputs than the standard variety - Russet Burbank. This increase in profits represented a 35% annual return on all the costs associated with all the breeding and testing programs conducted in the PNW over the last decade. At present, Ranger Russet and Umatilla only represent about 16% of the total potato acres in the PNW. Estimated benefits arising from these two new cultivars are expected to increase to over $ 200 million as they continue to displace Russet Burbank.

Source : Araji and Love (2002). Amer J. Potato Res. 79.

One a Day Potatoes ?

Contrary to some recent bad press, potatoes actually represent a good source of many important dietary nutrients, including ascorbic acid (vitamin C). A single raw potato contains more than 45% of the recommended daily allowance of vitamin C. All forms of cooking reduce the vitamin C content, but the actual amount lost varies greatly between cooking methods. French fries and baked potatoes retain 50-80% of their original vitamin C content, while mashed potatoes and chips retain only 25-35%. Given the importance of potatoes as a source of vitamin C, there is considerable interest in improving their ascorbic acid content - this is reflected in the increasing popularity of yellow fleshed varieties in North American markets. The vitamin C content of some of most popular varieties is presented in Table 1. Although Ranger Russet had a high vitamin C content, its values varied greatly between years and locations. The vitamin C content of Yukon Gold was more stable and dependable.

Table 1. Ascorbic acid content (mg/g) of potatoes varieties - averaged over 3 locations and two years.

Ranger Russet 29.4 Shepody 25.5
Yukon Gold 29.3 NorDonna 16.5
Gem Russet 26.1 Cherry Red 14.9

Source : Love, Salaiz, Shafii, Price, Mosley, and Thornton. (2004). HortScience 39:156-160.

Patchy Potatoes and Viruses - What's the Connection ?

The aphids that spread viruses in seed and commercial potato crops are attracted to areas of high color contrast in the field ... like the contrast between the green of the crop and the dark color of exposed soil. This explains why problems with PVY and PLRV tend to be worse at field margins, as these high contrast areas attract aphids. Consequently, planting down field margins and aisle ways to cover crops represents a sound approach to virus management in seed fields.

Gaps within the field caused by seedpiece failure, poor planter performance or drown-outs represent another high contrast area attractive to aphids. Davis, Radcliffe and Ragsdale found gaps bigger than 0.6 m in length within the row (ie; 3 seedpieces missing in a row) created at situation attractive to aphids and the adjacent plants consequently had a higher than normal incidence of infection with PVY.

In a survey of commercial potato fields Pavek and Thornton (2005) found that having 500 or more gaps of this size per hectare planted was not uncommon. While this problem was serious, the solution was also straight-forward - just insure a complete stand by having a skilled operator using an accurate planter to plant high quality seed into suitable field conditions. The author recognized that in the real world gaps will occur. They tried seeding down these gaps with oats worked to repel the aphids but a more practical approach may be simply let the weeds fill in the gaps. Spraying the plants adjacent to the gaps with insecticides did not protect them from virus infection.

Sources : Davis, Radcliffe and Ragsdale (2009). Amer. J. Potato Res. 86:203-208.
Pavek and Thornton (2005). Amer. J. Potato Res. 82: 463-469.

Planting Depth Effects

Planting depth of seed potatoes represents a compromise. Shallow planting into warm surface soil promotes rapid crop emergence, thereby reducing problems with seed piece decay and rhizoctonia attacking the stems. The shallow planted crop gets off to a quick start which may provide an edge in competition against weeds. Quick canopy development may also enhance yields, especially in areas with a limited growing season. However, shallow planting does not always result in optimum yields, as it appears the shallow planted crop may be more prone to heat and drought stress. The biggest problem with shallow planting is that it limits the space available under the hill. This leaves varieties, like Shepody, that tend to produce large tubers high up on the stem susceptible to having the tubers exposed to sunlight (greening), frost damage or invasion by diseases such as late blight. The various effects of planting depth were nicely illustrated in a study of Russet Burbank and Umatilla conducted by Pavek and Thornton (2009). They found that deeper planting (25 cm versus 10 cm) slowed emergence to a degree proportional to the soil cooling that occurred with increasing depth in the soil. Increasing the planting depth also slowed canopy development early in the season but by the end of their 150 day growing season canopy size was similar for all planting depths. The impact of planting depth on stem counts and stolon number varied between years and cultivars - however planting depth ultimately had no impact on tuber number per plant, tuber size or overall yields. They found that most tubers developed on the bottom 1/3 of the stem, with the largest tubers forming at the base of the stem. Because of the limited space available for tuber development, there was a 5 fold increase in grade out due to tuber greening in the shallow planted crop, leading to the deeper planted crop having a higher net market value.

Source : Pavek and Thornton (2009). Amer. J. Potato Res. 86: 56-67

Phosphorous Nutrition as a Tool for Tuber Size Management

An adequate supply of soil phosphorus (P) is critical to the development of all crops, especially potatoes. The shallow and relatively course root system of the potato plant, couple with the immobile nature of P in the soil profile makes it imperative that grower provides adequate supplies of P in close proximity the developing root system. It is difficult to harm potato plants by applying excessive amounts of P. However, rising fertilizer costs, coupled with concerns over the negative environmental impact of excessive use of P fertilizers are pushing growers to optimize their P fertility program. Rosen and Bierman (2008) looked at the impact of differing rates and forms of P applied in a band at planting or in a split application at planting and emergence. They found that the form of P applied and the timing application had little impact on any of the yield parameters measured. Yields were marginally increased by increasing rates of applied P, but almost all of the yield increase was due to a significant increase in the number of tubers set/plant. The observed reduction in average tuber size with increasing rates of P may be attractive to seed growers but may be less desirable for potatoes destined for processing or table markets.

Source : Rosen and Bierman. Amer. J. Potato Res. (2008). 85: 110-120.

Precision Agriculture and Potatoes - Lots of Questions Remaining

Yields and quality of potatoes can vary greatly within a relatively small area of a field. Researchers from Washington State used precision agriculture technology to show that, at most, 40% of the yield variability within a field could be explained by differences in soil properties (fertility, pH, texture, chemistry) across the field. They found that the most important soil characteristic governing yield also varied from field to field and season to season. In hot, dry years, soil textural components that promoted soil water retention (ie; high clay and organic matter content) were associated with improved yields. However, in wetter years or low areas of the field, a high clay content actually reduced yields. Changes in soil pH increased yields if they also resulted in improved nutrient availability. Specific gravities declined as soil K levels increased - otherwise soil characteristics had little impact on processing quality.

Source: Redulla, Davenport, Evans, Hattendorf, Alva and Boydston (2002). Amer. J. Potato Res. 79: 317-323.

Raised Beds a Better Idea for Potatoes ?

Methods of field preparation that promote drying and warming of the soil in the spring may allow earlier planting thereby potentially increasing yields. This effect would be particularly beneficial when long season varieties like Russet Burbank are grown in areas with a short and cool growing season. Essah and Honeycutt found that planting potatoes into raised beds or ridges created the previous fall accelerated crop emergence and improved yields and quality of Russet Burbank planted in Maine. The benefits of these fall tillage systems were particularly apparent in years with a cold wet spring. In drier spring weather, the raised beds provided no advantage in terms of early emergence. However, later in the season, the raised beds helped conserve soil moisture, resulting in higher yields under non-irrigated conditions. The concept of raised beds or ridge tillage is being used by growers in southern Alberta to accelerate development and improve yields of processing-type potatoes. These growers caution that while the raised beds seem to do a good job of capturing snow, they can increase problems with soil erosion due to wind action in both the fall and in the spring prior to planting.

Source : Essah and Honeycutt (2004). Amer. J. Potato Res. 81:177-186.

Redder is Better in Table Potatoes

Skin color is critical to marketing of table potatoes - but is particularly important in markets that prefer red potatoes. The factors that govern both the color of freshly harvested red potatoes and the retention of their color during storage are complex. Concentrations of the anthocyanin pigments that give the skin its red color are influenced by growing conditions - in general conditions that favor development of a healthy crop (warm days, cool nights and steady moisture supplies) also lead to good color. The red color tends to fade as the tubers mature in the field. This fading is particularly noticeable if soil temperatures stay high after top kill. Delaying top kill until conditions are cool may consequently improve crop color. Low storage temperatures (4C) slow but do not stop the fading of the red skin color. As the crop ages in storage, the rate of color loss accelerates - this is particularly noticeable once the tubers are moved out of cold storage and into the warm conditions of the supermarket. Research conducted by the University of Saskatchewan showed that Norland potatoes lost more of their red color during 7 days of storage at 20C (simulating supermarket conditions) than was lost during 4 months storage at 4C. The more highly colored strains of Norland (Red and Dark Red Norland) start off with superior color at harvest time, but fade as rapidly during storage as the standard strain. The Red and Dark Red strains of Norland do not actually differ in the amount of red pigments in their skin, but the skin of the Dark Red type contains higher concentrations of other pigments - giving the tubers a darker appearance. AC Peregrine, which is a new variety exclusively licenced to the SSPGA, not only starts out with superior color to the various strains of Norland - but its color also fades more slowly during both low and high temperature storage.

Sources : A. Anderson, C. Tong and D. Krueger.(2002) Amer. J. Potato Res. 79:249-253.
S. Agblor and D. Waterer (2002). AFIF - Horticulture Post-Harvest Research Program.

Reducing Nitrate Loss from Potato Fields

Potato production represents a potential source of nitrate pollution of groundwater due to; a) the high rates of fertilizer N applied to the crop, b) the low rate of N recovery by the crop, c) extensive irrigation of potatoes tends to drive the nitrates down through the soil profile, and d) the sandy soils preferred in potato production are prone to nutrient loss through leaching. Of the N applied to a typical potato crop, fully 50% is lost to leaching or denitrification, about 25% is removed from the field in the form of the harvested crop, with the remaining 25% stays in the root zone in the form of available soil nitrates or crop residues. By increasing the nitrogen use efficiency of their crop, potato growers can maintain productivity while reducing input costs and the safeguarding the environment. This objective can be achieved by;

1) matching the fertilizer nitrate supply to crop demand. This can be achieved by tailoring the total amount of N applied to match the specific requirements of the cultivar being grown - for example in Saskatchewan optimum yields of irrigated cv. Norland can be achieved through application of 150 #/a N, while cv. Shepody and Russet Norkotah appear to require up to 200 # N/a. Split applications of N are recommended in areas where heavy feeding, slow maturing varieties are grown under heavy irrigation on leaching prone coarse textured soils. Band application of N fertilizers in close proximity to the effective root zone can enhance N-use efficiency without risking salt burn. In-season tissues tests allow growers to insure that the N requirements of the crop are being met but not exceeded.

2) using formulations of N fertilizer with reduced leaching potential. Urea-based fertilizers or slow release formulations are particularly useful when the majority of the crop's N fertility needs are applied prior to planting. The nutrient release profile of these controlled release products tends to closely match the actual nutrient needs of the potato crop - leaving little nitrate available for leaching loss.

3) keeping track of N credits left in the field by previous crops (especially legumes) or by any manure applied within the rotation period. A significant portion of the organic N tied up in these crop residues or manure will be released as nitrate over the course of a typical growing season.

4) reducing leaching by more closely matching irrigation timing and rates to crop demand. This is especially important on leaching prone coarse textured sandy soils. More accurate field ready methods of assessing soil moisture status are required.

5) reducing the leaching tendency of the soil by increasing or at least safeguarding the soil organic matter content. A high organic matter content also encourages development of a deep healthy root system capable of scavenging for nutrients. 6) wherever possible using fall planted cover crops to sponge up any nitrates left over at the end of the growing season. Fast growing deep rooted crops like fall rye are particularly effective. The ground cover provided by these crops also protects the harvested potato fields from wind and water erosion. Where cover crops are not feasible, try to insure that the next crop in the rotation has the aggressive growth habit and deep root system that will capture any nitrates left over from the previous potato crop before they are leached into the ground water.

Sources : Shrestha et. al. (2010). American Journal Potato Research 87: 229-244. Waterer (1997). Canadian Journal Plant Sciences 77: 273-278.

Role of Fusarium sp. in Tuber Dry Rot

Fusarium dry rot is one of the most widespread and costly storage diseases of potato tubers. Fusarium sambucinum is the Fusarium species most commonly isolated from dry rot affected tubers - this reflects the fact that F. sambucinum is widespread, highly aggressive and largely resistant to the fungicides presently registered for post-harvest application to potatoes. There are however other Fusarium species that may also cause dry rot if conditions are suitable. Peters et al (2008) examined the relative pathogenicity of a range of the Fusarium species commonly encountered in potato fields across N. America. As expected, F. sambucinum, along with F. coerulum and F. solani caused the most damage when introduced into Norland, Yukon Gold or Russet Burbank tubers. These Fusarium species are commonly found in fields frequently cropped to potatoes or related crops like tomato. By contrast, the Fusarium species commonly found on forage crops like clover and alfalfa showed limited ability to infect or cause rot in potato tubers. However, the Fusarium species that cause head blight and root rot in grain fields (F. graminearum and F. avenaceum) also proved to be quite efficient at causing tuber dry rot. This is a concern as cereals are essential to potato crop rotations and these Fusarium species are capable of surviving for extended periods in the soil and in crop debris. The potential involvement of F. graminearum in tuber dry rot is particularly troubling as this Fusarium species produces substantial quantities of toxins which could limit the use of infected tubers as either food or feed.

Source : Peters et al (2008). Amer. J. Potato Res. 85:367-374.

So, How Much Frost Can a Potato Actually Take ?

Unfortunately, fall frost always seems to catch a few acres in Saskatchewan - leaving growers asking some of the following questions;

  • a) why were some tubers completely frozen, while others appeared unharmed
  • b) were the tubers that appeared unharmed ... actually damaged ?
  • c) is there something I could have done to prevent the problem (other than harvesting faster) ?

A study by Boydston and associates published in the July 2006 issue of the American Journal of Potato Research provides some answers. In a series of laboratory and field experiments they looked at some of the factors that influence which tubers freeze, how fast they freeze and the impact of low temperatures on sprouting - an issue of obvious importance to anybody selling or buying seed that has potentially been exposed to damaging temperatures .

They observed considerable variability from tuber to tuber in the temperatures required to trigger freezing. Although most tubers froze when exposed to -2C for an extended period, some tubers could be cooled to -6C with no apparent damage if these tubers were slowly rewarmed prior to handling. Any handling at these extremely low temperatures appeared to trigger ice formation within these tubers - leading to the typical symptoms of frost damage. These results underscore the recommendation to avoid harvesting a frost affected crop until it has had a chance to rewarm. Size (and maturity) of the tubers had no real impact on the freezing reaction. Differences between varieties were also minimal. This runs contrary to popular wisdom that some varieties appear much more frost prone than others. The reason for this apparent contradiction is straight forward - although varieties are very similar in their actual freezing point, they vary significantly in terms of the depth that the tubers are set. Boydston showed that soil is an excellent insulator ... with just a few cm of soil providing a significant degree of frost protection. Consequently varieties that set small tubers relatively deep (ie; R. Burbank) tend to be much less prone to frost damage that varieties that set high in the hill (ie; Norland) or varieties that produce large tubers that tend to erupt from the side of the hill (ie; Shepody). Growers can exert some degree of control over the tuber depth by managing planting depth, soil moisture levels, and hill shape and size. Adding to the hill prior to a frost event may be worth considering, but would only be practical in situations where crop residues have either died back or have been removed via flailing.

Although soil moisture content had little effect on the temperature at which potatoes froze, adding moisture to the soil almost doubled the time required for soil temperatures to drop below the freezing point of buried tubers. When water in the soil freezes it actually gives off heat - and that heat is transferred to any tubers in the vicinity. These results support the practice of irrigating when frost threatens - especially if the water source is still holding heat from a long hot summer.

Although tubers could tolerate cooling to -2C before visible symptoms of freezing damage became apparent (ie leaking of damaged tissues), other forms of damage were occurring prior to actual freezing. Although tubers exposed to -1.5C never showed any signs of frost damage irrespective of the duration of exposure, holding at that temperature for as little as 4h slowed sprout growth by 50% in subsequent performance trials. The extent of this chilling damage increased as the temperature dropped and/or the duration of exposure increased. Growers need to be aware of the potential for chilling damage to occur prior to harvest, during storage or during seed movement in the spring.

Source : Boydston, Seymour, Brown and Alva (2006). Amer. J. Potato Res. 83: 305-316.

Some Late Blight Spores Tougher Than They Look

Late Blight infections produce huge numbers of thin-walled sporangia (spores) which are easily dislodged by wind or water splash - resulting in rapid spread of the disease. These sporangia were thought to be extremely sensitive to dehydration - and dry weather was counted on to limit the rate and distance of spread of Late Blight. Sunseri, Johnson and Das Gupta recently examined the influence of sunlight, humidity, and temperature on the survival of A2 U.S. 8 type Late Blight sporangia. They found that the Blight spores could only tolerate a couple of hours exposure to direct sunlight - even if temperatures were cool and humidities high. This limits dispersal of Blight to night time or overcast days. The researchers were surprised to find that some spores of U.S. 8 blight survived and produced infections at humidities as low as 25% - as long as the weather was also cool. This reinforces local growers’ experience with the U.S. 8 strain of Blight - it appears to be well suited to the dry, cool conditions characteristic of potato production on the Canadian Prairies.

Source : Sunseri, Johnston and Das Gupta (2002). Amer. J. Potato Res. 79.

Sprout Inhibition in Potatoes - Changes Coming ?

Widespread use of the chemical sprout inhibitor CIPC (chlorpropham) allows efficient longterm storage of varieties (ie; Norland) that have a relatively short fall dormancy period. In 2002, as part of a regulatory review of the consumer safety of CIPC, residual tolerances for this chemical were reduced to 30 ppm from the previous allowable limit of 50 ppm. In Europe maximum tolerances have been dropped to 5 ppm. This drive towards using lower concentrations of CIPC may adversely affect both the duration and thoroughness of the resulting sprout inhibition - increasing the risk of product failure or creating the need for multiple applications. Researchers continue to look for safer, effective alternatives to CIPC. Carvone which is a naturally occurring volatile compound extracted from dill, mint and caraway has proven to be as effective at low dosages as CIPC - but with several advantages. Carvone inhibits sprouting but unlike CIPC it does not permanently damage the sprouts. Normal sprouting resumes once carvone treatments cease - meaning that carvone may be useful to both table and seed growers. Carvone vapors also have antifungal properties - Drs Tanino, Bandera and Thomson at the University of Saskatchewan have shown that concentrations of carvone that were effective at suppressing sprouting also reduced incidence and severity of fusarium dry rot in the stored crop. One limitation of using volatile essential oils as sprout inhibitors is the risk that the crop may begin to smell or taste of the essential oil. Trials conducted at the U of S showed that odor/flavor transfer varied with the chemical applied, the time since application and the method used to cook the potatoes. Odor/flavor transfer would we less of an issue in seed potatoes. Further research into optimum formulations, concentrations and methods of application will hopefully produce viable alternative methods for managing sprouting.

Source : Kleinkopf,, Oberg and Olsen (2003). Amer. J. Potato Res. 80:317-327.

Susceptibility of Russet Norkotah to PVY

Russet Norkotah is renowned for its poor field expression of symptoms of potato virus Y (PVY). Researchers from South and North Dakota have determined that this limited expression of symptoms does not reflect either a lack of infection or reduced development of the virus within the Norkotah plants. In fact Norkotah is an excellent host for the virus, but it simply fails to express clear foliar symptoms or much yield depression as a result of infection. Growers should be aware of Norkotahs’ potential to act as a hidden reservoir for PVY on their farm. Laboratory testing Norkotahs may be a useful additional step for growers concerned about rooting out any hidden infections by PVY .

Source : Draper, Pasche and Gudmestad (2002). Amer. J. Potato Res. 79:155-165.

Time Running Out on Another Control Product for Colorado Potato Beetles?

Colorado Potato Beetles (CPB) have a long track record of developing resistance to insecticides - in some cases, new insecticides were no longer effective within a year or two of release. Over the past few years potato growers in N. America have come to rely almost exclusively on neonicotinoid insecticides (ex: Admire) for CPB control. However, this heavy reliance appears to be selecting for resistance to this pesticide group as well. Alyokhin and associates (Amer. J. Potato Res. 2006 83: 485-494) have been studying a population of neonicotinoid resistant CPB that has arisen in Maine. This area has had previous problems with CPB populations developing resistance to other insecticides. In tests conducted in 2003, they found that this population was 30-50 X more resistant to neonicotinoid pesticides than normal - resulting in 80% defoliation of the neonicotinoid treated test plots by the season end. They noted that the neonicotinoid resistant beetles were still somewhat sensitive to other insecticides - but the overall level of insect control that could be achieved was still unacceptably low. On the upside, they noted that the neonicotinoid resistant CPB population was not as vigorous as normal. A decline in overall fitness has been observed in other insecticide-resistant CPB populations.

Although neonicotinoid resistant populations of CPB beetles have been identified there is no reason that this resistance has to become a real problem ... providing growers follow basic resistance management practices.

  1. report any indications of resistance to your input supplier and/or your local agrologists
  2. follow the product label recommendations regarding treatments rates, methods of application and especially the recommendation against applying neonicotinoids as both seed and foliar treatments
  3. rotate neonicotinoids with insecticides in different chemical classes. Be aware that neonicotinoids are market under many names (Admire, Gaucho, Platinum, Cruiser, Actera, Assail and others)
  4. if practical, only treat the field margins. This will provide good beetle control in the areas of the field that typically have damaging beetle populations but will leave a few untreated beetles around to cross breed with any beetles that were able to survive the insecticide treatment. This will reduce the potential for any pesticide resistant beetle to meet and mate with another resistant beetle - resulting in super resistant off spring.
  5. increasing the distance between last years field and this years field will reduce the likelihood that any resistant beetles left over from last year’s crop will be able to find and colonize this year’s field.

For more information on resistance management contact the local technical representatives for the company that supplies your favorite CPB control product.

Source : Alyokhin et al. (2006) Amer. J. Potato Res. 83: 485-494

Traditional Production Practices Limit Losses to Late Blight

Although foliar damage by Late Blight is common in traditional potato production systems in Equador, losses to tuber decay during storage are not significant. By contrast, tuber decay is common when Late Blight hits in most areas where potatoes are grown. Researchers investigating this difference have come up with the following potential explanations; a) potatoes in Equador are grown on soils that are resistant to cracking during wet/dry cycles. Cracks represent a means whereby the Late Blight spores produced by the infected foliage can come in contact with the tubers. b) potatoes are widely spaced both within and between the rows in the Equador production system. This allows the growers to develop very large hills (up to 3' in diam and 2' high). The large hills protect the tubers from both frost damage and the Late Blight spores that wash from the infected foliage. The wide spacing would also improve air flow within the canopy, thereby slowing both the development of foliar symptoms of late Blight and production of the spores that go on to infect the tubers. Although the traditional productions systems utilized in Equador are not practical in Saskatchewan, their success in managing Late Blight suggests the care in field selection and hilling could be useful aspect of an integrated management plan for this disease problem.

Source : Oyarzun et al., 2005. Amer. J. Potato Res. 82: 117-122.

Variability of Russet Norkotah Line Selections

In a statistical analysis of the growth and yield characteristics of several line selections of Russet Norkotah, Creighton-Miller and others found that there were significant differences between the selections for flower number, tuber shape and tuber yields. In general, the line selections were higher yielding, with smoother tubers than the original Russet Norkotah. Contrary to expectations, they could find no differences in vine size or vigor between the line selections and the original Russet Norkotah. They also found that differences in appearance and yield potential of any given line selection from year to year and field to field were much greater than any differences between lines.

Source : Creighton-Miller, Tai, Ouellette and Miller (2004). Amer. J. Potato Res. 821: 203-207.

Where Did That Scab Problem Come From ?

The question as to how scab problems arise is still generating some controversy. Problems can arise in fields with no history of potato production. This suggests that either the scab organism can survive on hosts other than potatoes or that soil-borne inoculum is constantly being introduced into fields by wind or water movement. Although scabby seed is widely regarded as another potential source of inoculum ... the relative importance of seed contamination in determining incidence and severity of scab is unclear. Pavlista (1996) found that seed-borne scab had little influence on scab levels in subsequent crops. Research conducted by the University of Saskatchewan has also shown little direct association between scab levels on the seed and scab levels on the resulting crop. However, recent work by Wang and Lazarovits (2005) suggests that seed-borne scab can be very important ... particularly if the seed is being planted into fields with no previous history of scab problems. They found that significant amounts of the scab organism could be found on the surface of seed potatoes that were apparently free of classic scab lesions. When this apparently scab free seed was planted into clean soil, almost 60% of the tubers in the resulting crop had visually detectable scab lesions. Starting with low populations on the seed, the scab organisms multiplied rapidly ... and by the end of the season could be found in very significant numbers on the roots, on the surface of the tubers and in the soil in the immediate vicinity of the infected plant. This suggests how scab problems can arise - even when growers plant apparently clean seed. Their research does however emphasize that planting “clean” seed does slow the build up of scab populations. This is important as they found a direct relationship between scab populations in the soil and subsequent grade losses due to scab.

Sources : Pavlista (1996). Amer J. Potato Res 73: 275-278.
Wang and Lazarovits (2005). Amer J. Potato Res 82: 221-230.

Who's Who of Potato Eaters

In a recent survey of CDN households ... 85% had fresh potatoes on hand, 46% had at least one frozen potato product (ie; French fries, hash browns etc), 44% had chips and 14% had some form of dehydrated potato product (ie; instant potatoes). The survey also identified 5 basic types of potato consumers/shoppers.
  1. The "Quick Fix" shopper - these constituted 29% of the survey population. They were typically relatively well off financially but squeezed for time. These consumers ate potatoes about twice/week and tended to purchase small quantities of potatoes, preferring fresh or easily prepared types of product.
  2. The "Healthy Eaters" - constituted 24% of the survey population. This group identified a focus on health in their diet and lifestyle. They tended to be older with no children still at home. The time required to prepare their meals was less of a concern than the nutritional quality of the meal. This group of consumers ate potatoes about 4 times/week and purchased fresh potatoes almost exclusively ... staying away from the processed potato products as they were regarded as less healthy.
  3. The "Couch Potatoes" - represented 20% of the survey population. This group ate all types of potato products, as long as they were convenient to purchase and prepare. This group was relatively young and was unconcerned about the nutritional quality of their meals.
  4. The "Foodies" - represented 17% of the survey. This relatively new and fast growing group of people take their food very seriously. They follow trends in cuisine like the "slow food" movement. Unfortunately potatoes are not trendy within this group at the present time.
  5. The "Potato Heads" - represented only 9% of the survey. These people eat a lot of potatoes ie; > 10 servings/week. They typically had large households and appeared to appreciate the good food value provided by potatoes. These households typically bought potatoes in bulk formats.
It is clear that potato consumers in Canada are a diverse group with differing needs and expectations for potato products. However, the survey results also indicated some common themes ... suggesting that the hypothetical "Perfect Potato" should ....

- Be easy to peel with no eyes (sorry seed potato growers)

- Have fewer carbs and less fat. The low fat issue is interesting as fresh potatoes are already effectively fat free. Processed potato products still have room for improvement in this area.

- Be high in vitamins and other nutritional valuable compounds. This is again interesting as potatoes are already rich in a range of vitamins and minerals. The desire for "even more" of these elements suggests a potential market for specialty potatoes with an enhanced nutritional profile ie; highly colored varieties with greater antioxidant activity

- Small size

Source : Canadian Potato Business (2008)

Yukon Gem - A New Yellow Fleshed Table Potato

Yukon Gem was developed by a breeding consortium in the north-central United States. It is the result of a cross between Yukon Gold – the present industry standard for yellow fleshed table potatoes and Brodick, a Scottish variety renowned for its disease resistance. Yukon Gem produces a moderate size plant with upright stems. It responds well to close in-row spacings and its soil fertility requirements are moderate. Yukon Gem grows and matures at about the same rate as Yukon Gold. The tubers are also similar in appearance to Yukon Gold, with an oval shape, smooth yellow skin and bright yellow flesh.  In trials conducted in the U.S.A. over the past 8 years and in Saskatchewan in 2010, Yukon Gem proved superior to Yukon Gold in a number of respects. Yukon Gem yields were 10-20% higher than Yukon Gold and it produced fewer oversized hollow tubers. Yukon Gem is significantly more resistant to late blight, common scab and several damaging viral diseases than Yukon Gold. Yukon Gem also proved to be superior to Yukon Gold in taste trials (boiled and baked) conducted by the University of Saskatchewan in 2010 and it produces exceptionally high quality tasty French fries. Yukon Gem stores well under standard conditions. 

The combination of high yields, moderate input requirements, disease resistance and superior flavour makes Yukon Gem well suited to use by commercial, organic and hobby growers. Seed should be commercially available by 2012.            

University of Saskatchewan