Cucurbit Downy Mildew | Cornell Vegetables

Updated July 2022

This is one of the most common and destructive diseases affecting all cucurbit crops in the eastern United States including New York. Occurrence varies spatially and temporally year to year with movement of this wind-dispersed pathogen. There are some resistant cucumber varieties. Fungicides are the main management practice.

Listen to Meg McGrath talk about managing downy mildew in a teleconference hosted by Steve Bogash of Marrone Bio Innovations on 17 June 2020. Dial 515-604-9875. At prompts enter 832191 for access code and 9 for reference number.

Detailed information about downy mildew and its management are in the following articles and tables:

Downy Mildew of Cucurbits factsheet
Downy mildew: Early symptoms (LIHREC)
Downy mildew: Other symptoms and imitators (LIHREC)
Managing Cucurbit Downy Mildew
Cucurbit Downy Mildew Forecasting Program
Mobile fungicides for managing downy mildew and other major cucurbit diseases
List of biopesticides for organic production

Symptoms

cucumber leaf with downy mildew — Symptoms of downy mildew on upper surfaces of cucumber leaves. Leaf in the center is the leaf in the second image.

close-up of cucumber leaf with downy mildew — Symptoms of downy mildew lower surface of cucumber leaf. Pathogen sporulation is below the yellow and brown symptoms visible on the upper surface (first image).

More information/prepared by:

Margaret Tuttle McGrath
Associate Professor
Long Island Horticultural Research and Extension Center (LIHREC)
Plant Pathology and Plant-Microbe Biology Section
School of Integrative Plant Science
College of Agriculture and Life Sciences
Cornell University
mtm3@cornell.edu