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Vegetable Disease Updates for August 2, 2017

Posted: August 2, 2017

On August 1st, late blight was confirmed on tomato in a small commercial planting in Chester County, PA.
Map of cucurbit downy mildew currently reported along the east coast as of 2 August 2017 (cdm.ipmpipe.org).

Map of cucurbit downy mildew currently reported along the east coast as of 2 August 2017 (cdm.ipmpipe.org).

This is not surprising given the recent cooler wet weather which favors not only late blight but other diseases caused by Phytophthora spp. Late last week, late blight was also suspected in a potato field in eastern Pennsylvania however those symptoms were thought to be caused by a different species of Phytophthora, Phytophthora nicotianae. Under very wet conditions this pathogen can cause buckeye rot on tomato fruit close to the soil and on potato it can cause foliar symptoms similar to late blight and tuber symptoms similar to pink rot, typically caused by P. erythroseptica.

late blight tomato leaf

Characteristic late blight foliar lesion on tomato. Photo: B. Gugino, Penn State

In addition this past week, there have been new reports of late blight on tomato in Steuben County, NY just north of Tioga County, PA and on tomato in Massachusetts. All the reports on the east coast this season have been genotyped as US 23 so both tomato and potato crops are potentially at risk. A protectant spray program which includes chlorothalonil, mancozeb or copper for diseases such as early blight or Septoria leaf spot will also help protect against late blight. If growing tomatoes or potatoes in Chester County including a late blight specific fungicide such as Previcur Flex, Ranman, Zampro or Orondis Opti is recommended. See the Mid-Atlantic Vegetable Production Recommendations for additional recommendations. 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.

If you suspect late blight on your farm, please contact your local Penn State Extension Office or let Beth Gugino know via email at bkgugino@psu.edu 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 USABlight.org.

Weather Continues to Favor Cucurbit Downy Mildew

Downy mildew disease pressure continues to build. Currently it has been confirmed in 14 counties across Pennsylvania. Cucumber continues to be the primary host however there are also several reports on cantaloupe and a couple on butternut squash across the region. The nearest reports on jack-lantern type pumpkin remain in South Carolina and Mississippi.

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

Fusarium Crown and Root Rot

If your squash and pumpkins are collapsing, Fusarium crown and root rot may be the cause. Although all cucurbit crops are susceptible at all ages, pumpkins and squash (Cucurbita pepo) are especially susceptible. Usually, the first symptoms observed are a yellowing and wilting of the leaves which develop as a result of a rotting of the roots. The root rot starts as a water soaked area found at the base of the crown and upper portions of the taproot. It is not uncommon for infected portions of the roots can develop pinkish color. This soilborne fungal pathogen can also cause a fruit rot on fruit that are either wounded or come in contact with the soil at the soil surface. The sunken round to oblong, tan to brown lesions will remain firm unless colonized by secondary decay organisms. This disease is exacerbated by high soil moisture levels.

The pathogen can be both soilborne and seedborne. It can survive in the soil 2 to 3 years so at least a 4-year rotation out of cucurbits is recommended. Seed treatments containing thiram can help to reduce transmission from the seed to the young seedling. In-season management options are limited. Applications of Proline (propiconazole; PHI 7 days) may reduce symptoms if used early in the season.

above ground yellowing

Photo 1

fusarium on pumpkin

Photo 2 (left) and Photo 3 (right). Above ground yellowing and wilting symptoms resulting from a below ground root rot caused by Fusarium on pumpkin. (Photos 1 and 2) The pinkish roots characteristic of Fusarium can be seen in the lower right (Photo 3). Photos: B. Gugino, Penn State

Contact Information

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