How to treat powdery mildew on squash and cucumber plants? Most of our squash plants have powdery mildew. Some of the leaves have died and crumbled. We had same problem last year. I regret not removing all the infected plants before tilling the soil last year. How can we eradicate this mildew and keep it from coming back next year? I cut off some of the leaves, but felt it may be too big of a shock to the plant.
Powdery mildew is a common issue in the Willamette Valley, and on the coastal range of Oregon. There are several fungi that can cause powdery mildew, each with various optimum environments.
While complete control of powdery mildew is difficult in squash, there are some ways to mitigate for it. There are varieties of squash that are more resistant to powdery mildew, which can be planted in your garden. For example, if you want to grow zucchini, you could choose Payroll or Sebring. A more complete list can be found from Cornell University.
Reducing humidity can also reduce the amount of powdery mildew growth you have on your squash. Pruning back plants, and planting farther apart to encourage air circulation can reduce the amount mildew that grows on your plants.
Irrigation can also help reduce the incidence of powdery mildew in your garden. While overhead watering can reduce the amount of powdery mildew on your plants, it can increase humidity and cause other fungal pathogens to grow, so it is not recommended. Instead, use drip irrigation when possible, and irrigate when the water is absorbed before it can become humid.
If you have space, crop rotation is also an effective method to reduce the buildup of powdery mildew in your soil. Rotating your crops so that you only have squash in one area of your garden every 3–4 years can help reduce the buildup of the pathogens.
Removal of diseased plants and materials will help lower the pathogen load as well. Do not compost or reincorporate diseased material into your soil. Instead, dispose of it off-site.
Pesticides are usually not warranted for powdery mildew in the home garden. However, if you are producing for sales, or in large quantities, contact your local extension office to discuss treatment options.
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Use pesticides safely!
- Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.
- Read the pesticide label—even if you’ve used the pesticide before. Follow closely the instructions on the label (and any other directions you have).
- Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use.
