Jul 27, 2017

Weather favors cucurbit downy mildew

Currently it has been confirmed in eleven counties in central and southern Pennsylvania with an unconfirmed report on cucumber in western Pennsylvania.

Cucumber continues to be the primary host however there are also several reports on cantaloupe across the region. The nearest reports on jack-lantern type pumpkin are in South Carolina and Mississippi.

With successive cucumber plantings, once harvest is complete, disk or burn down the crop debris to reduce the further movement of downy mildew inoculum into the younger plantings. As with late blight, once the plant tissue is dead, the pathogen is dead. Also maintain a regular fungicide spray program on the later plantings. Cucurbits are susceptible to downy mildew at any stage of growth.

Downy mildew can often be confused with the bacterial disease angular leaf spot (see comparison photos below). The symptoms are very similar; the lesions are initially water soaked in appearance before turning brown or straw-colored and are also vein limited. The lesions will often dry and drop out, leaving irregular shaped holes in the leaves. If you do not see downy mildew sporulation on the underside of the leaf in the field, place several symptomatic leaves in a sealed bag overnight and then check for purplish gray sporulation the next day.

 For the latest information on outbreaks and to receive email or text alerts please visit the Cucurbit Downy Mildew Forecasting website. Updates will also be made to the 1-800-PENN-IPM hotline weekly or more frequently if needed to provide growers with information that can be used to help make timely management decisions. The forecasted risk maps are also based on knowing where there are downy mildew infected fields (sources of the pathogen) so it is important if you suspect downy mildew on your farm contact Beth Gugino by email at [email protected] or by phone at 814-865-7328 or contact your local Penn State Extension Office.

Photo above: Cucumber leaf showing symptoms of both angular leaf spot and downy mildew. Downy mildew lesions have purplish gray sporulation on the underside of the leaves (upper right) while those infected with angular leaf spot do not (lower right). Photos: Beth K. Gugino, Penn State

– Beth Gugino, Penn State University

Source: Penn State University