The unseasonably wet weather this summer is starting to take a toll on some cucurbit crops, according to Virginia Cooperative Extension agriculture agent Scott McElfresh.
Cucurbits include squash, pumpkins, cucumbers, gourds, watermelons and cantaloupes, but McElfresh said cucurbit downy mildew (CDM) is starting to show up on cucumbers, butternut squash and pumpkins across the Commonwealth.
Initially, the disease causes small yellow spots on the upper surface of the lower leaves. However, blue/gray spores develop on the underside of leaves in high humidity, especially during the morning hours.
Untreated, the leaves eventually die, exposing the fruits or vegetables to sunscald. Entire crops of susceptible plants have been lost to the disease.
McElfresh said persons growing these crops are urged to thoroughly inspect plants for the disease and consider taking preventative action. Products containing the active ingredient chlorothalonil, mancozeb, maneb or copper have been successful in controlling the disease.
The treatment should be applied at the first sign of the disease or after runners have formed on plants. Reapply the product every seven days or every five days if conditions are favorable for spread of disease.
He stressed that label directions should always be followed and plant sensitivity referenced since some melon varieties may be sensitive to maneb.
To help protect plants from the disease when planting, avoid low-lying fields and look for cultivars of cucumbers that are less susceptible to downy mildew. Excessive overhead irrigation should also be avoided.
Additional information on the disease is available at http://pubs.ext.vt.edu/450/450-707/450-707.html
If you think cucurbit downy mildew is present in your fields or if you have questions, call McElfresh at 980-7761 or email email@example.com.