July 8, 2011

This year the ergot fungus infected wheat in south central and southeast Nebraska to a greater extent than we’ve seen in recent years, causing problems for growers and elevators. This article provides information on the disease and what growers can do to reduce potential problems next year.

What is ergot?

Ergot is a disease of the inflorescence of cereals and grasses caused by the fungus Claviceps purpurea. Ergots, compact masses of fungal mycelium also known as sclerotia, are produced instead of normal grain (Figures 1 and 2).

Occurrence

The ergot fungus is endemic to the Great Plains wheat producing region of North America. It occurs to some extent every year in cereal grains, pasture and roadside grasses in Nebraska. Among the cultivated cereals, ergot is more common in rye and triticale than in wheat, barley, and oat. Many wild and cultivated grasses are also susceptible.

Symptoms

The first sign of infection by the ergot fungus is the appearance of a sugary yellowish slime (honeydew) on the wheat head at or soon after flowering. Later, ergots (scelorotia) develop and are the most noticeable and characteristic sign of ergot. They are horn-like, purple-black, and 4 to 10 times the normal size of grain. On the head, they replace developing grain and protrude beyond the glumes (Figure 1).

Disease Cycle

Sclerotia from previous cereal crops or indigenous grasses survive in or on the soil surface. When subjected to cold temperatures and spring moisture, they germinate and form fruiting structures which release sexual spores known as ascospores. The ascospores are dispersed by wind and splashing rain. When their release coincides with plant flowering, the ascospores land on the florets and infect the ovaries. One to many ovaries may be infected per head. Following infection, the ovaries swell into structures known as stromata (singular: stroma). These are compact masses of specialized hyphae of the fungus that eventually develop into ergots. Asexual spores known as conidia are produced superficially on the stromata in honeydew. Insects are attracted to feed on the honeydew. The conidia are spread to other florets by insects, direct contact, and rain splash and infect the ovaries. The disease cycle is completed when sclerotia mature on the heads and fall to the ground during harvest or are introduced when contaminated grain is planted.

Favorable Environmental Conditions

Cool, wet weather during flowering favors infection by ascospores and conidia. The most susceptible hosts are those with prolonged flowering periods and more open florets. Often, indigenous grasses are the main source of spores that infect wheat and other cereals. Many of the ergots in wheat grain may be from weedy grasses. These ergots are usually smaller and more slender than those produced on wheat.

Ergot Alkaloids

The ergots contain poisonous compounds known as alkaloids. Ingestion of ergots in grain and flour can cause illness or death in humans and domesticated animals. Ergotism in humans is known as St. Anthony's fire and has occurred several times in human history, with serious consequences. It is thought that the Salem witchcraft trials of 1692 resulted from hallucinations and insanity caused by ingestion of ergoty flour. Animals that have consumed feed contaminated with ergots can exhibit an acute form of ergotism characterized by convulsions or a chronic form characterized by gangrene. Other forms of ergotism in animals include hyperthermia (high body temperature), lack of milk production, lack of mammary gland development, prolonged gestations, and early foal deaths in mares.

What To Do If You Have Ergot In Your Wheat Grain

Most, but not all, ergots can be removed from grain by cleaning it with gravity-type cleaning equipment. Small, high value seed lots can be cleaned by flotation in brine (20% salt solution). The sclerotia float and the grain sinks in the brine solution.

Do not feed ergot-contaminated grain to livestock. Wheat straw from harvested fields can be fed to livestock since the ergots will have been harvested along with the grain or fallen on the ground. (The ergots, not the straw, are poisonous.) However, wheat straw should not be baled for feed if it still has ergoty heads.

Management of Ergot

• Use sclerotia-free seed to plant the next wheat crop.
   
• Mow grasses in headlands, roadsides, and waterways before they head.
   
• The survival rate of sclerotia on the soil surface is about one year. Crop rotation with non-host crops such as legumes, corn, and sorghum reduces the risk of carryover infections from sclerotia within the field.
   
• Plow fields with heavy ergot infestations to bury sclerotia. Burying sclerotia more than one inch deep will prevent them from germinating

More Information

For more information on ergot, check these resources:

• EC1874, Fungal Diseases Affecting Grain and Seed Quality in Wheat
• PP-551, Ergot
• RPD No. 107, Ergot of Cereals and Grasses

Stephen Wegulo
Extension Plant Pathologist, Lincoln