Vegetable Disease Updates for July 18, 2017

Updates on downy mildew on cucumber, late blight on tomato and potato, and Septoria on tomato.
Vegetable Disease Updates for July 18, 2017 - News


Map of cucurbit downy mildew currently reported along the east coast as of 20 July 2017 (

Downy Mildew is Widespread on Cucumbers Across Central and Southern Pennsylvania

New reports of downy mildew on cucumber are being confirmed daily with downy mildew now reported in commercial fields in Columbia, Montour, Northumberland, Mifflin, Juniata, Blair, and Lancaster as well as suspected in Cumberland and Franklin counties. There are also been several reports on cantaloupe and one report on butternut squash. The continued unsettled weather patterns across the state have been favorable for disease spread and development. The continued incorporation of downy mildew specific fungicides is recommended especially on cucumber and cantaloupe.

Be sure to rotate among FRAC (Fungicide Resistance Action Committee) code numbers to ensure that you are rotating between different modes of action. Also tank mix downy mildew specific fungicides with a broad-spectrum fungicide like chlorothalonil (labelled on all cucurbits with a 0 day PHI) or mancozeb (only labelled on cucumbers, cantaloupe/ muskmelon and summer squash with a 5 day PHI) for fungicide resistance management. Continue scouting all cucurbit crops and if not already, consider using of a broad-spectrum protectant fungicide to help protect against downy mildew as well as other common foliar diseases.

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 or by phone at 814-865-7328 or contact your local Penn State Extension Office.

Still No Reports of Late Blight on Tomato and Potato in Pennsylvania

To-date, there are no confirmed reports of late blight in Pennsylvania. Within the past 7 days there has been one additional report of late blight on potato in Livingston County, NY. Other previous reports of late blight nearby include tomato in Ontario, Canada and potato in Michigan, the eastern shore of Virginia and in Erie County, NY.

Although there are currently no reports of late blight in Pennsylvania it is still important to scout higher risk areas of the field including low lying areas or shaded field edges and potato cull piles for symptomatic volunteers. If you suspect late blight on your farm, please contact your local Penn State Extension Office or let Beth Gugino know via email at or by phone at 814-865-7328. We are interested in collecting samples so we can better understand how the pathogen population is changing both within and across growing seasons. Also for the information regarding where the latest confirmed outbreaks have been reported and to receive email or text alerts about when late blight has been confirmed with a personally defined radius from your location visit

Be on the Lookout for Common Summertime Tomato Foliar Fungal Diseases

It's the time of year when we start to see an increase in early blight and Septoria leaf spot in commercial tomato fields. For both diseases symptoms tend to start on the lower (oldest) leaves and then work their way up the plant to the youngest leaves and are spread by rain splash during heavy rain events. When left unmanaged they can quickly defoliate the plant. Foliar lesions are initially small dark spots but as they enlarge early blight lesions will develop concentric rings while Septoria leaf spot lesions will become tan in the center with a dark margin and small dark specks in the center (pycnidia which are more visible with the aid of a hand lens). Septoria does not infect the fruit. Early blight develops under warm temperatures (75 to 85°F) and high relative humidity, heavy dews or significant rainfall while Septoria leaf spot prefers slightly cooler temperatures between 68 and 77°F.

During the season, maximizing air flow by suckering and staking and tying the plants and minimizing working the field when it is wet will help minimize spread. Protectant fungicides like chlorothalonil, mancozeb, Gavel (contains mancozeb) and Zing! (contains chlorothalonil) will also help reduce spread but good coverage is important. They are most effective when applications are started when the crown fruit are one-third of their final size.

Symptoms of Septoria leaf spot (top) and early blight (bottom) on tomato Photos: Beth K. Gugino, Penn State