July 2, 2014: Phytophthora Blight Coming on Strong in Peppers and Cucurbits

Phytophthora lesion on pepper leaf

With the long period of rainy weather and warming temperatures, Phytophthora blight is appearing in peppers and cucurbits throughout Ohio.   The pathogen moves from plant-plant and field-field in rainwater irrigation water, and runoff water.  It survives in ponds, streams and rivers – we have tested several of these in Ohio and found them to be contaminated with Phytophthora capsici, the causal agent of Phytophthora blight.  Phytophthora can survive several years in the absence of host plants.

Pepper plant (middle) killed by Phytophthora blight

In addition to peppers and cucurbits, tomatoes, eggplant, snap beans and certain weeds are susceptible to Phytophthora blight.  There are no cucurbit varieties resistant to Phytophthora blight.  Cucurbits should not be planted in fields with a history of Phytophthora blight until after at least 4 years in non-susceptible rotation crops.  Pepper varieties with varying degrees of resistance to the root and crown rot phase include Paladin, Aristotle and Vanguard.  These varieties are not resistant to foliar blight and fruit rot.

Powdery white mold typical of Phytophthora blight on cucumber fruit

Phytophthora blight must be managed using an approach that integrates crop rotation, disease resistance (peppers), cultural practices to reduce water accumulation near plants, avoidance of Phytophthora-contaminated water, sanitation of tools and equipment, and fungicides.  Recommended fungicides are listed in the 2014 Midwest Vegetable Production Guide for Commercial Growers.  Keep in mind that fungicides alone will not control Phytophthora blight; and even with integration are not fully effective.  Some Phytophthora populations have developed resistance to fungicides.  Note that pre-harvest intervals (PHIs) vary from 0-5 days.  Always follow a fungicide resistance management program (see product label).

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