Downy Mildew Resistant Cucumbers

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

With downy mildew being found in pickling cucumbers on Delmarva, resistant varieties should be considered.

We now have several slicing and pickling cucumbers with some degree of resistance to the current aggressive cucumber downy mildew strain. According to Clemson University new research has identified two strains of cucurbit downy mildew: A1 attacks cucumber and cantaloupes (the most aggressive strain), while A2 attacks watermelon, pumpkins, and squashes.

In gynoecious slicing cucumbers, Bristol, SV3462CS and SV4719CS and associated pollenizers have intermediate resistance to cucumber downy mildew. In gynoecious pickles, Citadel, Peacemaker, and SVCN6404 with associated pollenizers have intermediate resistance. Next generation downy mildew resistant varieties are being tested this year on Delmarva.

These varieties are not immune to downy mildew, but they show less disease under the same pressure and will out yield susceptible varieties. Under disease pressure they perform best with a fungicide program using downy mildew materials. Research is being conducted to see if there is the potential to reduce fungicide applications.

Shown in the table below is the yield of pickling cucumber varieties with and without intermediate resistance to cucumber downy mildew with one fungicide application for downy mildew under moderate disease pressure. Note that the resistant varieties significantly outperformed the susceptible variety (Georgetown, DE, 2017).

Downy mildew pressure with susceptible and resistant varieties planted side by side in a trial located on the Eastern Shore of Maryland in 2018.