Vegetable Crop Diseases – September 11, 2009

Bob Mulrooney, Extension Plant Pathologist;

Lima Beans
Continue to scout for downy mildew. The recent weather is very favorable for downy mildew. If downy is found apply RidomilGold/Copper, Phostrol or other labeled phosphorus acid (phosphonate) fungicide. If disease has not appeared in the field Headline, Forum or fixed copper fungicide can be applied preventatively in addition to Ridomil Gold/Copper and phosphorus acid fungicides.

Sweet Corn
Field corn is not the only host for the fungus that caused Northern corn leaf blight. I have seen several fields of sweet corn recently with very high levels of infection clear to the top of the plant. Ears from badly infected plants were not filled out and will not be worth harvesting. Northern has been favored by the cooler and wetter season.

Northern corn leafblightTypical large lesion (3-4 inches long) caused by Northern corn leaf blight

Late blight
is resurging on backyard tomato plantings at the present time. There is nothing besides chlorothalonil and mancozeb for homeowners but late season commercial planting should be protected from late blight with any of the late blight specific fungicides.

Cole Crops
Downy mildew and Alternaria
can be a problem in fall cole crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears apply a fungicide every 7 to 10 days. Quadris, chlorothalonil, Cabrio, Endura (Alternaria only) Maneb, Ridomil Gold Bravo, Switch (Alternaria only), Actigard (downy mildew only) and Aliette (downy mildew only) are labeled for control. For more information on control please see the 2009 Delaware Commercial Vegetable Production Recommendations.

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