Jul 9, 2020

Northeast growers monitor diseases following dry June

June proved to be a dry month across much of Pennsylvania and the Northeast region except for a few areas around Harrisburg and Scranton that received normal to slight above-normal precipitation.

The average precipitation across the state was 3.11 inches, 72% of normal, while temperatures averaged from normal to slightly warmer than normal with an average temperature of 67.3° F. This along with other current and historical weather data and narrative summaries can be found at the Northeast Regional Climate Center.

There continue to be no reports of late blight on tomato or potato in the region. If you suspect late blight on your farm please let me know either by email at [email protected] or by phone at 814-865-7328 or contact your local Extension Office.

Be on the lookout for downy mildew on cucumbers and cantaloupe.

There have been several reports of downy mildew on cucumber in the surrounding states over the past couple of days. These include one report in southern New Jersey, two reports in western New York along Lake Erie and Lake Ontario, and a report in the most southern tip of Ontario, Canada.

There have also been two unconfirmed reports of downy mildew on cucumber in the south-central part of Pennsylvania near Chambersburg and Waynesboro. Please be scouting all cucumber and cantaloupe fields for downy mildew.

The pathogen is spread from known sources of the disease over large distances along the wind trajectories. The spores will be killed when exposed to several hours of direct sunlight however, cloud cover protects them and when there are rain events, they are “washed out” of the sky and deposited on the cucurbit crop below.

When conditions are considered low risk (yellow) when nearly all the factors needed for pathogen spread and disease development are unfavorable so the forecast might be sunny to partly cloudy and dry. Under moderate risk (orange), the conditions are mixed but still skewed toward favorable so the conditions may be partly sunny to partly cloudy with a chance of scattered showers. The risk is highest (red) when conditions are cloudy, and rain is likely. Conditions may not be favorable during the day but could turn favorable overnight. Keep in mind that the color-coded regions are not only based on the forecasted weather conditions but also centered around confirmed reports of the disease.

– Beth K. Gugino, professor vegetable pathology, Penn State University

Downy mildew on upper surface of cantaloupe leaves. Photo: Beth Gugino/Penn State