Cucurbit Downy Mildew Present in Western North Carolina

— Written By

people in squash research plot at field day

We are conducting screening trials for the multi-state Organic Cucurbit Breeding project. We are growing cucumber, melon, and squash varieties and breeding lines and looking for resistance to several diseases and insects. The most important disease we want resistance to is Downy Mildew. Usually it is a huge problem for us and takes down susceptible plants by mid-July. But this year, our field plots look great because we have not had Downy Mildew. But, that will probably end soon as Downy Mildew has been diagnosed in the region, as our pathologist, Inga Meadows, explains in this article:

Cucurbit Downy Mildew Found in Ashe and Haywood Counties

– Written By Inga Meadows, Plant Pathologist, NC State University

Cucurbit downy mildew has been reported on pumpkin and cucumber in Ashe and Haywood Counties, respectively. Downy mildew, caused by the oomycete Pseudoperonospora cubensis, infects leaves and can result in significant yield loss.

It was reported through the CDM IPMPipe on pumpkin in Ashe County on August 10, 2016 and by an NCDA Agronomist in Haywood County on August 12, 2016.

Cucurbit downy mildew is a foliar disease that affects all commercial cucurbits (cucumber, cantaloupe, squash, watermelon, pumpkin, etc.), but is most severe on cucumbers. Growers are advised to actively scout for the disease and initiate preventative sprays in cucurbit crops immediately.

The Cucurbit Downy Mildew factsheet, previous alerts, North Carolina fungicide efficacy trials, and The Southeastern US Vegetable Crop Handbook provide recommendations for chemical control options. Growers should use intensive spray programs (every 5-7 days) once disease if found in their fields, especially if weather conditions are conducive to disease (wet and cool weather). The downy mildew pathogen can become resistant to fungicides very quickly. It is critical that growers alternate products in their fungicide programs and tank-mix with a protectant with every application to protect the few chemistries we have that are still highly effective in controlling downy mildew.

If you think you have downy mildew in your field, please contact your local Extension agent and send photos and/or physical samples to the Plant Disease and Insect Clinic. Reporting the occurrence of cucurbit downy mildew to the CDM IPM pipe helps us protect our state’s cucurbit industry by providing them with timely disease management information.