Ergot

Claviceps purpurea

Biology

Ergot infects many cereals and grasses; these include (in order of decreasing susceptibility), rye, triticale, wheat and barley. Oats are rarely affected.

Ergot overwinters as black grain-sized fungal structures. In late spring, these ergots germinate and form tiny spore-producing mushroom-like structures. Infectious spores are carried by wind currents to the host during the flowering stage. Infection of the cereal flowers may produce a secondary phase called honeydew. Honeydew is a shiny sticky liquid that oozes from infected flowers and contains large numbers of ergot spores. The spores spread to adjacent flowers and heads by insects and rain splash particularly to the open flowers of rye. Ergot that germinates in June can infect early flowering weed grasses, which produce honeydew when cereals are flowering.

Cool, damp weather in late spring and early summer favours ergot germination, helps prolong the flowering period of cereals and grasses, and increases the probability of ergot infection.

The presence of ergot in wheat and barley in Alberta has been strongly correlated with soils that are low in copper, or with management practices that cause a copper deficiency in cereals. Wheat, and barley, grown on copper deficient soils have a high rate of pollen sterility. Barley and wheat are self-pollinating and the florets normally do not open. If the pollen is sterile, florets of wheat and barley open and expose the stigmas to ergot infection. Male sterile lines of wheat and barley are very susceptible to ergot infection and have been abandoned in plant breeding. Open florets are very obvious in wheat growing on copper deficient soils.

Some herbicides may disrupt copper availability. Manure applications and high application rates of nitrogen and phosphate fertilizer may tie-up available copper, particularly on soils already low in this micro-nutrient. All of these factors singly or combined may contribute to copper deficiency resulting in greatly reduced yields and vastly increased infection rates of ergot in barley and wheat.

Damage Description

Ergot is most easily recognized by the hard black bodies that replace the grains of the affected head. Heads may contain one or more ergots. Earlier in the season, before the ergots are produced, an amber liquid or honeydew can be detected on individual flower heads. Heads collect dust and pollen on the sticky honeydew and may appear dirty.

Ergot bodies are highly poisonous. Alkaloids in ergot are extremely toxic to humans and livestock. Ergot alkaloids have been detected in flour and cereals intended for human as well as animal feeds. For cattle, 0.5 per cent by weight of ergot in the diet causes reduced feed consumption and weight loss. Economic losses also result through reduction of yield and through rejection or downgrading of contaminated grain by the elevator. Yields are occasionally reduced by as much as 5 per cent in rye and 10 per cent in wheat.

Diagnosis

The Canadian Seeds Act (July 1987) defines the maximum number of ergots allowed per kilogram of seed before the sample is downgraded.

	Maximum number of ergots/kg
Grade	Wheat	Barley & oats	Triticale and rye
Canada Foundation #1	1	1	2
Canada Foundation #2	8	8	10
Canada Registered #1	1	1	2
Canada Registered #2	8	8	10
Canada Certified #1	1	2	4
Canada Certified #2	8	8	15
Common #1	1	2	4
Common #2	8	8	15

Ergot can move into a field through contaminated seed but usually the source of inoculum is infected grasses in the headlands. When the disease source is the headland grass the highest density of ergoty cereals is around the perimeter along the headlands. If the infected plants are more evenly distributed throughout the crop, the disease source is likely from contaminated seed or a previously infected crop. Knowledge of the distribution pattern is important at grain harvest. Under very windy conditions in standing grain that is mature or nearly so, the ergots often protruding in infected heads will get shaken or knocked off. This will reduce the amount of ergot in the harvested grain by up to 70% or more.
Cereal spikes containing ergot have fewer kernels per head with less weight per seed. Yield loss percentage for rye can be estimated as follows:

Percent loss = % ergoty spikes x (1 - seed weight of ergoty spike) / seed weight of healthy spike

Management Strategy and Control

Reduce inoculum levels and apply copper fertilizer to reduce or eliminate this disease in wheat and barley. With adequate soil copper, all cereals except rye will have little or no ergot infection. Some herbicides and environmental conditions may interfere with normal growth and reduce available copper and, consequently, may result in ergot infection. Research in Finland has shown that soils low in boron induce pollen sterility in barley. Thus, in a similar manner to the pollen sterility caused by copper deficiency, the normally closed flowers of wheat, barley and oats will open and ergot infections occur.

• Test soils for copper availability; an application of copper fertilizer may be needed if levels are below 1 ppm in many soils.
• Use a rotation with non-host crops to reduce inoculum levels. Ergots rarely survive more than a year in the soil.
• Bury crop residue 2.5 cm or more into soil to prevent spore-producing "mushrooms" from emerging above ground.
• Delay swathing, particularly in headland areas if possible, because windy weather will shake out the ergots from standing grain.
• Mow headland grasses on a regular, annual basis well before seed set. This will prevent ergot production. Meadow foxtail is extremely susceptible to ergot.
• Harvest headland area swaths separately because they are likely to have the highest ergot contamination.
• Store ergoty grain intended for seed for two years. The ergots will die, but the grain will remain viable for many more years.

Severe ergot infection in barley head.

Heavy ergot infestation of barley seed.

Ergots germinate on the soil surface in June/July to form minute "mushrooms" that release ergot spores.

Ergot on oat. The black sclerotia replaces a kernel.

Mushroom-like structure that grow from germinated ergots (June/July) which fell to the ground the previous year. These mushroom like structures produce conidia (spores) that infect open cereal flowers, particularly rye. Ergo in cereals other than rye is often a very good indication of copper or possibly boron deficiency.

Ergot in rye. Ergots are poisonous to livestock.

Ergot in wheat, black sclerotia replacing kernels.

Healthy grain and an ergot of wheat. Poisonous ergots in wheat are highly symptomatic of copper deficiency of the crop.