Following heavy rainfalls from the storms over Labor Day weekend in Illinois, a University of Illinois crop scientist warns vegetable growers to be on the lookout for outbreaks of downy mildew of basils, downy mildew of cucurbits, Phytophthora blight of cucurbits, and Phytophthora blight of peppers throughout the state.
“These diseases are caused by oomycete pathogens,” said Mohammad Babadoost, professor of crop sciences at the University of Illinois. “The excessive moisture in the soil due to the recent rainfall makes conditions perfect for these pathogens to spread. We will closely monitor the development of these diseases and release recommendations, as needed,” he said.
Downy mildew of basil, caused by the oomycete pathogen Peronospora belbahrii, is a new disease in Illinois, first detected in 2009. This disease now occurs in Illinois every year. Downy mildew develops very rapidly and can cause 100% crop loss in a short period of time. Growers may not realize their basil has a disease because the most noticeable symptom on affected plants is yellowing, resembling a nutritional deficiency.
Downy mildew, caused by Pseudoperonospora cubensis, affects all cucurbit crops (cucumber, gourd, muskmelon, pumpkin, squash, watermelon, zucchini). The pathogen overwinters in the southern U.S. where cucurbits are grown during the winter. It progresses northward with cucurbit production each spring. The pathogen might have moved from the South to Illinois by the Isaac storm. The first symptom of cucurbit downy mildew is usually the appearance of indistinct, pale green areas on the upper leaf surface.
Phytophthora blight, caused by Phytophthora capsici, is one of the most serious diseases of cucurbits and peppers in Illinois. It will likely develop in cucurbit and pepper fields with a history of Phytophthora blight. The infection usually appears first in low areas of the fields where soil remains wet longer. P. capsici causes crown rot, vine lesions, and fruit rot in cucurbits, and root rot and crown rot of peppers.
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