Phytophthora Blight Management in Cucumber

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu and Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Heavy localized rainfall in our region has resulted in pockets of Phytophthora blight, especially on cucumber. While there is no way to avoid these rain events, there are practices and products that can alleviate some of the losses to Phytophthora blight. Management of Phytophthora blight should be based on cultural practices that minimize standing water on the crop. This means planting only in fields with good drainage, not planting in low areas, subsoiling fields before planting, avoiding over-irrigation, etc.

Several fungicides are registered for managing Phytophthora blight. While the labels may say “control”, it is more accurate to say these fungicides will “suppress” Phytophthora blight because the control is easily overcome if the weather favors disease development. The organism that causes Phytophthora blight is related to the one that causes downy mildew, therefore some of the fungicides can be used to target both diseases.

Below is a table that indicates which products are effective on downy mildew, and have some suppression on Phytophthora blight. Relative efficacy is not listed for Phytophthora blight because little comparison data exists.

Fungicide Efficacy on Downy Mildew and Phytophthora Blight