By Carol Traulsen
It’s the scourge of my garden. In fact, last year it ruined two plants that most gardeners agree are typically the hardiest: zucchini and cucumber plants. What am I referring to? Powdery mildew of course. They are caused by a number of species of fungi in the order Erysiphales. It’s easy to spot. The affected plants display white powdery spots on the stems and leaves. It affects mostly the lower leaves, but any portion of the plant that is above ground can be affected. As the disease progresses, the spots get larger and denser and the mildew may spread up and down the length of the plant. Powdery mildew grows well in environments with high humidity and moderate temperatures.
It’s actually a variety of fungi that affect ornamentals such as bee balm, zinnias, roses and phlox. It also affects vegetables such as beans, cucumbers, grapes and squash. So why is it a problem? It’s unattractive and can reduce the yield of some fruits and vegetables. Although the plants are unattractive and weakened- the plant doesn’t die. Powdery mildew on ornamentals is an aesthetic issue and generally not worth treating. Prevention and control is more important for vegetables.
I couldn’t believe it when I saw these powdery white spots on the plants that were supposed to be the easiest plants to grow. How could I have messed up growing zucchini and cucumber? After all you’ve heard the saying that you only need one zucchini for the neighborhood. Cucumber isn’t any harder (normally). I panicked when the spots first appeared, I thought perhaps water had gotten on the leaves and they’d remained wet. But neither my husband nor I watered the plants from the top. Water was always poured around the bottom of the plants.
After reading up on it I discovered that you may be able to control the spread by picking or cutting off the affected leaves. For a while I thought I was making progress, but the vines began to wither, the squash and the cucumber were strange looking. I tried home remedies like spraying the leaves with milk or baking soda, but neither worked. If I picked any more leaves off there would be nothing left of the plants, then production stopped all together. With half a summer left I had nothing. No more zucchini for bread or muffins and no more cucumbers for salad. There really was nothing left to do. I pulled up the plants and packed it in for the season. I felt like a failure. Any idiot can grow a zucchini or so I thought.
I was dismayed to learn that once the plant has it can’t be cured. The key is to get a variety of plant that is resistant. The more tolerant varieties may get some mildew but it shouldn’t affect the performance of the plant. We purchased our plants at the same place we always did, but I don’t think last year’s were a resistant variety. Making sure the plant is exposed to as much sunlight as possible is important as well. This inhibits spore production. Other than these few tips, I haven’t found anything that works. It’s beyond my control.
Gardening is different every year. There will always be things you can’t control, whether it’s the elements or pests or fungal diseases. This year the powdery mildew came back but late in the season. The zucchini and cucumber plants are done for the year. The pumpkins have a touch of it but they’re just about ready to be picked. What makes up for it is that when one plant struggles another usually flourishes. This year it’s my tomatoes. I have more than I can possibly use. Last year it was green beans and peas. Things balance out if we give them a chance and remain hopeful. Scourge can turn to reward, and pestilence to perfection. It just depends on your mindset.