Plant Diseases
Wheat Diseases in Arkansas
Downy Mildew
Downy
mildew, caused by the fungus Sclerophthora macrospora, frequently occurs in
areas of fields subject to flooding. Symptoms appear in the spring as stunted
yellow plants. Severely stunted plants have many tiny stems and usually die
before heading. Leaves of infected plants feel thick and leathery. Less severely
infected plants may elongate and produce distorted heads with no grain.
The pathogen attacks wheat, oats, barley, rice, corn, sorghum and about 140
species of wild grasses. All adapted wheats are believed to be susceptible. The
fungus produces thick-walled survival spores within infected tissue. Under
flooded conditions these germinate to produce several motile spores that "swim"
in water. These penetrate leaf sheaths, and then the fungus becomes systemic
within the plant. Seedlings are more susceptible than adult plants.
Avoiding areas prone to flooding and providing for adequate drainage of
surface water are the best means of controlling downy mildew. Apron fungicide
seed treatment, which is registered for control of Pythium root rot, may provide
protection against downy mildew for a few weeks after planting. However, under
Arkansas conditions flooding may occur over a period of several months after
planting.
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