PUTNAM COUNTY — I made a quick trip around the garden this weekend and noted a couple of diseases on vegetable plants that you might be seeing as well.

If you have pumpkins or squash in your garden, you have likely noticed some changes to the plant leaves in the form of a powdery and/or fuzzy white substance on the upper and lower leaf surfaces (see image). These are tell-tale signs that your plants have a fungal disease - either powdery mildew or downy mildew.

Powdery mildew is common on a number of ornamental and vegetable plants including garden phlox, bee balm, lilac, zinnia, as well as lettuce, pumpkins, cantalope, cucumbers and squash. Watermelon is not usually affected by powdery mildew here in Ohio.

Powdery mildew develops under warm, relatively dry conditions and forms white, fluffy spores on upper and/or lower leaf surfaces and stems. Squash, melons, cucumbers and pumpkins are especially prone to developing powdery mildew and should be sprayed with a fungicide at the first sign of the disease. If left untreated, severely infected leaves will brown, shrivel and die, often weakening the plant and reducing yield.

Downy mildew also infects a number of vegetable plants, including cucumber, squash, pumpkins and watermelon. Downy mildew spores do not survive Ohio winters but instead travel up from the south on wind currents each year arriving in August through September. While in some years we do not have a problem with downy mildew, it is present this year. Water must be present on leaf surfaces for downy mildew to develop. Warm, humid conditions promote its rapid growth and spread.

Plants infected with downy mildew have gray, fuzzy patches on the underside of the leaves and pale green to yellow spots on upper leaf surfaces. In pumpkin, yellow lesions on the leaf are angular in shape. In watermelon, lesions are yellow and rounded turning brown to black over time. Once detected, plants can be sprayed with a fungicide to control the spread. Eliminating overhead watering and keeping foliage dry is also very important, though this is difficult with our recent summer rains.

Gardeners can take several steps to minimize each of these diseases in the home garden. The first step is growing tolerate or resistant varieties, when available. Some cucumber, cantaloupe and pumpkin varieties are resistant or partially resistant to powdery mildew and/or downy mildew. Select and apply fungicides labeled for use on vegetable crops if either disease is detected. Remove and properly dispose or compost diseased plant material to minimize spread to other plants.

For additional information, please contact the Putnam County Extension office at 419- 523-6294, by email at Scheckelhoff.11@ osu.edu or stop in at 1206 East Second