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Vegetable Disease Updates for June 30, 2017

Posted: June 30, 2017

Be on the lookout for downy mildew on cucumber and cantaloupe. Diseases such as Phytophthora blight, blackleg on potato and bacterial diseases that spread in some of the recent rain events that moved across the Pennsylvania as well as timber rot in high tunnel tomatoes.
Map of cucurbit downy mildew currently reported along the east coast as of 30 June 2017 (cdm.ipmpipe.org).

Map of cucurbit downy mildew currently reported along the east coast as of 30 June 2017 (cdm.ipmpipe.org).

Reports of Downy Mildew on Cucumber (and Other Cucurbits) are Increasing

Downy mildew was confirmed on cucumber and/or cantaloupe in northeast Ohio (Wayne Co.), Essex, ON (southeastern most tip of Ontario, Canada), southeast Michigan in Monroe Co., and southern New Jersey in Salem Co. Disease pressure is also continuing to build in North and South Carolina on cucumber and cantaloupe with more recent reports now on yellow/summer squash, butternut squash, giant pumpkin and watermelon. With the forecasted unsettled weather this weekend, it is important to consider applying at least a protectant fungicide on cucumber and cantaloupe. Since host resistance is not readily available, the timely application of effective fungicides is the primary tool for disease management.

See the 2017 Mid-Atlantic Commercial Vegetable Production Recommendations for the latest fungicide recommendations for non-certified organic production. For certified organic production, copper-based fungicides remain the primary tool and can be used in combination with products like Serenade, Regalia and Actinovate for suppression.

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 to let me know either by email at or by phone at 814-865-7328 or contact your local Penn State Cooperative Extension Office.

Wet Weather Equals Increasing Reports of Diseases on Vegetables

If you live in an area of the state that has been experiencing significant rainfall events, in low lying areas of your fields be on the lookout for symptoms of Phytophthora blight on cucurbit and peppers as well as blackleg or blackleg-like symptoms and late blight on potatoes (and tomatoes). The rain splash is also resulting in a general increase and spread of bacterial diseases across a number of different crops.

Timber Rot in High Tunnel Tomatoes

The cool and wet conditions this spring were ideal for timber rot to develop in high tunnel tomatoes and as a result we are receiving many questions about what to do next. Timber rot is caused by the same pathogen as white mold or Sclerotinia rot. The pathogen has a very wide host range that includes both cash crops as well as cover crops and weeds which makes crop rotation challenging unless you can rotate to a grain crop for an extended period of time. Therefore, sanitation is a critical component of timber rot management.

As the disease progresses, dark black structures known as sclerotia will develop in the infected tissue and if these structures fall into the soil they can survive up to 10 years or more. It is best to remove and destroy any infected tissue before the sclerotia develop. If sclerotia are visible, it is even more important to carefully remove and bag the plant in the high tunnel. The number and efficacy of fungicides for managing timber rot are limited (primarily Fontelis and Contans, a mycoparasite of the sclerotia) and are best applied when conditions are favorable for disease (prolonged moisture and temperatures <80F). For more information see Frequently Asked Questions about Timber Rot on Tomato.

timber rot on tomato

Brown lesion with white fluffy mycelium characteristic on timber rot stem symptoms. The black elongated structures are the sclerotia that develop in the tissue and can persist in the soil. Photo: B. Gugino, Penn State

Contact Information

Beth K. Gugino
  • Associate Professor Vegetable Pathology
Phone: 814-865-7328