Q: My cucumbers got powdery mildew, and the plant has pretty much died. Can I eat the cucumbers that are still on it? What should I do to avoid this problem next year?

A: Yes, if your plants get powdery mildew but still produce fruit, you can eat the fruit.

We’re hearing that this was a big year for powdery mildew. It’s always around, and it always hits some plants harder than others, but the right weather conditions can make it worse. My tomatillos got a bad case this year. I didn’t even know tomatillos were susceptible.

Powdery mildew is caused by several different closely related fungi. These fungi thrive in warm, humid conditions, and we certainly had those this summer. Powdery mildew forms white patches on the leaves of susceptible plants, which include many vegetables and ornamental plants. In the vegetable garden, powdery mildew can damage cucumbers, squashes, tomatoes, peppers, beets, melons, peas, beans, and a number of other crops. Different plants are affected by different fungi. The beans growing right next to my tomatillos were not affected at all.

If the conditions are right, the white patches on the leaves will spread to the whole plant. Often, powdery mildew hits late enough in the summer that you still get a crop, but it can reduce your yield significantly.

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Powdery mildew struck this zucchini plant, eliminating almost all food production. (News Tribune)
Powdery mildew struck this zucchini plant, eliminating almost all food production. (News Tribune)

Once your plant is in bad shape, there’s not much you can do. When the season is over, be sure to remove all the affected foliage from the garden. Don’t put it in your compost unless your compost pile gets hot. Take it to a garden waste disposal site such as WLSSD.

Next year, choose cultivars that are resistant to powdery mildew. Don’t plant susceptible plants in the same spot in the garden where you had powdery mildew in the past. Make sure not to crowd your plants, and remove any nearby weeds. Good air flow can help reduce the problem.

If you get powdery mildew year after year, you may want to consider using a fungicide. Keep a close eye on your plants and apply the fungicide as soon as the first spot appears. Remember that fungicides can harm beneficial insects, such as bees. Follow the directions on the label carefully.

There’s more information about powdery mildew on cucumbers and squashes here: https://extension.umn.edu/diseases/powdery-mildew-cucurbits.

Written by U of M Extension Master Gardeners in St. Louis County. Send questions to features@duluthnews.com.