Crop & Pest Report

Accessibility


| Share

Ergot Being Reported in Wheat (08/16/18)

The wheat harvest is in full swing and reports of ergot have been received from south central, east central and central North Dakota. Below, I will review some of the commonly asked questions with the disease.

Ergot Being Reported in Wheat

The wheat harvest is in full swing and reports of ergot have been received from south central, east central and central North Dakota. Below, I will review some of the commonly asked questions with the disease.

What causes ergot and how does it infect wheat?

Ergot is a fungal disease primarily caused by Claviceps purpurea. The pathogen has a very broad host range with reports of it infecting over 400 grass species including barley, durum, rye, spring wheat, winter wheat, quackgrass, and brome grass. The pathogen survives as hard-bodied fungal structures called sclerotia or ergot bodies. These sclerotia germinate in the spring giving rise to stroma (mushroom-like) that release hundreds of thousands spores during the growing season. Infection in wheat (or other small grains) occurs when spores land on flowers in the early stages of flowering; prior to the visual appearance of the yellow anthers on the center of the head. The spores will land on the stigma of the wheat flower and replace the developing kernel with strands of mycelial (fungal) growth. Successful infection will produce “honeydew” and will be visible prior to flowering (Figure 1). The sugary and sticky honeydew contains asexual spores that are often carried by insects to infect the flowers of other potential host plants/crops. Eventually, the fungal strands will replace the developing wheat kernel, harden and turn into a black-purple sclerotia (Figure 2). The sclerotia can be harvested with the grain or will fall to the soil and overwinter.

What conditions favor ergot?

All literature indicates cool and wet weather during wheat flowering favors sclerotia germination and infection. However, the definition of cool weather is loosely defined in literature. Our experience suggests that ergot is more apparent when temperatures are in the 70’s with ample moisture (dew or rain). Historical accounts of ergot epidemics in North Dakota in the 1920s suggest that prolonged periods of moisture in late June into early July were a major influencer of disease incidence.

Why are there strict thresholds for ergot?

Ergot sclerotia contain toxic alkaloids that can cause harmful effects in both humans in cattle. In humans, the alkaloids will reduce blood flow to limbs resulting in gangrenous symptoms. It also can cause hallucinations and has been linked to the Salem Witchcraft Trials, the weakening of Julius Caesar’s troops and the death of Russian soldiers in the late 1920’s. Livestock fed ergot sclerotia can develop gangrene symptoms of ears, hooves and tails. The alkaloids can also cause abortions and reduce mammary gland development. Therefore, ergoty seed lots should not be fed to livestock.

Management of ergot

  • Crop Rotation – Rotating a broadleaf or corn on a field with ergot will reduce the amount of in-field inoculum. The ergot will survive on the soil surface for about one year, so not providing an available host will reduce the chance of pathogen survival.
  • Tillage – Burying sclerotia at least one-inch into the soil will prevent the stromas (mushrooms) from reaching the soil surface and releasing spores.
  • Mowing or Preventing Grassy Weeds from Heading – Grassy weeds in field margins such as quackgrass or bromegrass will head and flower prior to the small grain crop. Preventing these grasses from heading will reduce the formation of ergot bodies and reduce the risk of spores being carried into small grain fields.
  • Use Ergot Free Seed – The use of ergot free seed will reduce the amount of in-field inoculum.
  • Host Resistance – To our knowledge, there are no small grain varieties with resistance to ergot. However, small grains that have a shorter flowering window are less susceptible. For example, rye tends to be the most susceptible small grain as the flowering process and opening of florets can extend several weeks in field. Observations of ergot in variety trials tend to relate to time of heading and flowering. In other words, varieties that were heading during a conducive time for ergot had a higher incidence than those that escaped the infection window. Other factors that prolong floret openings (cool weather, physiological components or copper deficiency) will increase the risk for ergot as well.
  • Fungicides – Foliar fungicides at heading have not been shown to be effective in managing ergot. Seed treatment fungicides on ergoty seed lots have been shown to delay and disrupt germination of sclerotia. Studies conducted overseas suggest that triazoles (FRAC 3) have reduced viability of sclerotia.
  • Harvesting Strategy – Due to the strict threshold level in wheat (< 0.05% by weight), it is important to scout fields for present of ergot. Often times, ergot incidence will be higher along field margins bordering a road ditch or section line where grassy weed hosts are present. If you notice a higher level along a field edge, keep that grain source separate from the rest of the field.
  • Cleaning an Ergoty Seed Lot – Cleaning using gravity-type or color sorters can help reduce (not eliminate) the amount of ergot sclerotia in a seed lot. Ergot sclerotia tend to be lighter and less dense allowing for the removal of these structures.

Friskop.1

Friskop.2

 

Andrew Friskop

Extension Plant Pathology, Cereal Crops

Joel Ransom

Extension Agronomist for Cereal Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

USDA logo

Creative Commons License
Feel free to use and share this content, but please do so under the conditions of our Creative Commons license and our Rules for Use. Thanks.