Vegetable Disease Updates for August 9, 2017

Late blight was confirmed on tomato in a home garden and is also suspected in a commercial tomato field in Indiana County.
Vegetable Disease Updates for August 9, 2017 - News


Characteristic whitish spores produced on the underside of a late blight infected tomato leaf is how the pathogen spreads. Photo: Beth K. Gugino, Penn State

Late Blight Confirmed on Tomato in Indiana and Chester Counties, PA

Additional reports of late blight are continuing to come in on tomato in Chester County. and it is also suspected on potato. The Chester County sample was genotyped as US23 so both tomato and potato crops in southeastern PA are at risk especially if the cooler wet weather persists. Late blight is favored by leaf wetness from rain or heavy dew and temperatures between 64 and 75°F.

Due to the highly favorable weather, it is advised that growers consider including a late blight specific fungicide in their spray programs. However, if your potato crop is near vine kill or already has been vine killed then this is not necessary. Late blight specific fungicides would include products such as but not limited to, Previcur Flex (FRAC 28), Ranman (21), Zampro (45+40) or Orondis Opti (U15+M5). See the Mid-Atlantic Vegetable Production Recommendations for additional recommendations. These products should be tank mixed with a protectant for fungicide resistance management and alternated/rotated between different FRAC codes. For organic growers, copper-based programs tend to be most effective. Another possible option would be to alternate between Regalia and Actinovate both tank mixed with a copper-based fungicide. These products are most effective when applied preventatively and regularly when conditions favor disease. Good spray coverage is essential.

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

Weather Continues to Favor Cucurbit Downy Mildew

Again this past week, downy mildew disease pressure continued to build. Currently it has been confirmed in 15 counties across Pennsylvania and is most wide spread on cucumber with additional reports on cantaloupe and butternut squash. Reports on processing and jack-o-lantern pumpkins are increasing along the east coast in North and South Carolina and most recently in Indiana. Long-distance movement of spores during storms from these locations can put our pumpkin fields at risk. Be scouting your pumpkin fields for downy mildew. On pumpkin, downy mildew will develop similar yellow and then tan/brown angular lesions on the upper leaf surface (although smaller than those on cucumber) and the characteristic purplish-gray sporulation on the lower leaf surface. Downy mildew does not cause any direct symptoms on the fruit. Protectant fungicides used to manage powdery mildew and fungicide resistance will also help protect against downy mildew. If you are still a number of weeks from harvest, consider including a downy mildew specific fungicide into your spray program. There are no cultivars resistant to downy mildew so fungicides are our primary management tool.

Upper and lower leaf symptoms of downy mildew on pumpkin. Photo: Beth K. Gugino, Penn State

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.

Yellowing Cantaloupe? Might Be Due to Phytotoxicity

Yellowing along the edges of cantaloupe leaves (marginal chlorosis) can be the result of salts accumulating along the leaf edges as a result of guttation (water drops along the edges of the leaves) in the morning. The water exuded by the leafs contains salts which are left when the leaves dry and can then concentrate along the leaf edge and lead to phytotoxicity or burning of the leaf edge. Frequent copper-based fungicide applications can result in a similar symptom and foliar fertilizers can exacerbate symptoms.

Marginal chlorosis on cantaloupe caused by frequent copper-based fungicide applications. Photo: Beth K. Gugino, Penn State

Spreader stickers and other adjuvents can also lead to phytotoxicity by aiding to draw the product into the leaf. Sensitivity can vary by cultivar, the combination and rates of products in the spray tank and the weather at the time of application. It is recommended that you keep detailed notes and scout your field post-application to check for possible phytotoxicty so that spray programs can be adjusted if needed.