Winter Wheat Production Manual

Written by D. B. Fowler
Crop Development Centre
University of Saskatchewan

© University of Saskatchewan. All rights reserved.  No part of the Winter Wheat Production Manual may be reproduced in any form by any photographic, electronic, mechanical or other means, or used in any information storage and retrieval system without the written permission of the University of Saskatchewan or Ducks Unlimited Canada.

Ergot

Ergot (Claviceps purpurea) is a common disease of cereals and grasses throughout the world. It is usually associated with rye, but it can cause economic losses in triticale and wheat and it is occasionally found in barley and oats. Both cultivated and wild grasses are susceptible hosts and they are important sources of inoculum for the infection of cereal crops.

[ Images | Causes and Symptons | Losses | Control ]


a) Causes and Symptoms:

The presence of purplish-black colored sclerotia (hard masses of mycelia that are the ergot resting stage) in the plant head or grain is the most obvious symptom of ergot infection. These dark elongated structures form in place of the kernel. They vary greatly in size and may be up to 10 times as large as a normal seed. Rye sclerotia are usually larger that those produced on wheat.

Ergot overwinters as sclerotia on the ground or mixed in with the harvested seed. Sclerotia usually only remain viable in the soil for one year, but they can be preserved for a longer period in stored grain. Sclerotia germinate in the late spring or early summer and produce tiny mushroom-like structures containing ascospores (sexual spores). The disease cycle is initiated each growing season when ascospores are spread onto the florets of flowering host plants by the wind.

Ascospore release must coincide with the flowering period of a host crop in order for ergot infection to take place. Once they have found their way into the flower of a host plant, it usually takes less than a day for ascospores to germinate and infect the ovary tissue. Conidia (asexual spores) are produced and secondary infection can occur within five to ten days after the initial infection. Droplets of a yellow, sticky, sugary liquid called "honeydew" are produced along with the conidia. The honeydew attracts insects that spread the conidia to previously uninfected florets. Conidia can also be spread by rain splash. Sclerotia eventually develop in place of the kernels in infected florets. When the infected crop matures, the sclerotia either fall to the ground or are harvested with the grain.

Ergot infection is favored by cool, wet weather and any other factor that increases the length of the crop flowering period. Late tillers, uneven flowering, and floret sterility also increase the likelihood of infection. The florets of open-pollinated crops like rye are more easily infected by ergot because they stay open longer than those of self-pollinated crops like wheat.

[ Images | Causes and Symptons | Losses | Control ]


b) Losses:

Ergot infestations do not normally cause significant reductions in grain yield. However, even a low level of ergot contamination is a major degrading factor that greatly discounts the market value of grain.

Ergot sclerotia contain alkaloids (some of which belong to the same group as lysergic acid diethylamide or LSD) that are responsible for a toxic condition known as ergotism. They cause irritability, reduced food intake, and unthriftiness in birds and animals. In extreme cases these alkaloids can result in convulsions, loss of body appendages (tails, ears, legs, etc.) due to gangrene, and death.

In humans, an alternate freezing and burning sensation associated with these problems is known as St. Anthony's Fire. While they are a contaminant in grain, ergot alkaloids have pharmaceutical value in stopping blood flow and relieving certain types of pain when administered in regulated amounts.

The levels of ergot that can be fed safely vary with the age and type of animal, the alkaloid concentration of the ergot, and the length of the period of consumption. Pregnant animals can be caused to abort when fed very low levels of ergot and young animals are more susceptible to its affects than adults. As little as 0.1 percent ergot by weight is usually considered the upper limit in feed rations while grain used for human consumption should be essentially ergot free.

In western Canada, ergot contamination greater than 0.05 percent is a degrading factor in rye and once levels reach 0.33 percent rye is downgraded to sample, which results in a considerable financial loss to the farmer. Tolerance levels vary in wheat depending on class, but 3 sclerotia per 500 gm of grain will usually drop wheat from the top grade and once ergot levels exceed 0.25 percent, wheat is graded sample.

Historically, fear of ergotism has been a deterrent to the use of rye in human foods and livestock feeds. However, improved production practices and modern cleaning and inspection methods have largely eliminated these concerns from the present day marketplace.

[ Images | Causes and Symptons | Losses | Control ]


c) Control:

1. Management is the most effective method of controlling ergot.

- Adopt management practices that ensure uniform heading of healthy vigorous crops. Management practices that promote uniform heading reduce the risk of inoculum build up and secondary infection.

- Plant seed that is free of ergot sclerotia. Modern seed cleaning equipment can remove most sclerotia.

- Grasses growing in neighbouring fields and along fence lines and headlands are a common source of ergot inoculum. Mowing these areas before the grasses head will reduce the opportunity for the build up of secondary inoculum.

- Ergot infestations are usually highest at the margins of fields. These areas of a field should be harvested and handled separately when ergot infestations are severe. Heavily contaminated seed should be disposed of by burying to destroy sclerotia and prevent access by livestock.

- Sclerotia will not germinate when they are buried by more than one or two inches (2.5 to 5 cm) of soil. Therefore, tillage operations that bury the sclerotia are a control option after severe ergot outbreaks.

- Sclerotia only remain viable for approximately one year under field conditions. Consequently, crop rotation away from susceptible grasses and cereals for a year will reduce the probability of ergot infection.

- Do not allow highly ergot susceptible volunteer plants to head. They can provide a bridge that allows ergot to survive between susceptible crops in rotations.

2. Grow winter (fall) rye rather than spring rye. Field trials in both Alberta and Saskatchewan indicate that the incidence of ergot is lower in the earlier maturing winter rye.

3. There are no recommended fungicide treatments for the control of ergot.

4. None of the commercially available cereal cultivars are resistant to ergot.

[ Images | Causes and Symptons | Losses | Control ]

 

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Figure 15 (a, b). The presence of purplish-black colored sclerotia on the head of the plant or grain is the most obvious sympton of ergot infection. (Image Size A = 34k) (Image Size B = 36k)