Downy mildew is affecting cucumber, melon, pumpkin, squash in WNY

cucurbit downy mildew on leaves in New York State
You can see the rectangular checkerboarding that stays within the boundaries of veins on leaves affected by cucurbit downy mildew (CDM). These photos were taken under 10x magnification using a hand lens held up to a smart phone. Photo courtesy Cornell Vegetable Specialist Elizabeth Buck

by Connie Oswald Stofko

If you’re having trouble with your cucumber, melon, pumpkin or squash this year, you’re not alone.

A disease called cucurbit downy mildew (CDM) has already been identified in Erie, Niagara, Orleans, Genesee, Wyoming and Cattaraugus counties. This map shows the spread of CDM.

Chautauqua County and Northern Pennsylvania expect to see the disease soon. Cornell Cooperative Extension in Chautauaqu County would like gardeners to send in samples of suspected cases of CDM. (See more below.)

Unfortunately, there’s not much home gardeners can do about this disease, said Emily Reynolds, executive director of Cornell Cooperative Extension in Chautauqua County. Most home remedies and off-the-shelf fungicide products do little to stop an infection.

Luckily, resistant varieties of plants are available and are a great choice for planting in home gardens next year, she said.

About cucurbit downy mildew

CDM causes rectangular checkerboarding that stays within the boundaries of veins.

The pathogen doesn’t affect fruit directly. The affected leaves die prematurely, which results in fewer fruits. The plant can also produce fruit of low quality, such as misshapen cucumbers, poor flavor or sunscald. (Sunscald occurs when the fruit is exposed directly to sunlight; a healthy plant has enough leaves to protect the fruit from too much light.)

Samples needed from Chautauqua County

Cornell’s vegetable specialists are looking to collect a few samples from Chautauqua County. Home gardeners should contact the Chautauqua County master gardeners at chautauquamg@cornell.edu, chautauqua@cornell.edu or 716-664-9502, ext.224.

Suspected cases of should be put into a zip seal baggie with a big breath of air or spritz of water and left on the counter overnight to force sporulation. Once sporulating, CDM can be visually confirmed by Cornell Cooperative Extension. 

The samples will help researchers find better controls of cucurbit downy mildew. Learn more about the disease here.

2 Comments on “Downy mildew is affecting cucumber, melon, pumpkin, squash in WNY

  1. Hi Connie, I’m so sorry to hear that! I know that some people cook zucchini flowers. Maybe you can get some harvest out of those.

  2. So what are we supposed to do? I harvested one good zucchini last week but this week the plant has CDM. Same for cucumbers. And the plants have many flowers (baby cucumbers . If the fruit is low quality and the leaves really look scary, I’m just going to pull the plants out before it spreads the disease to others and also leave the spores on the ground for next year. I pulled out the Eva Callum phlox this year due to powdery mildew which comes up every year- just couldn’t deal with it.

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