In central Utah, our growing season is relatively short. Our last spring frost comes rolling through in early June, and our first killing frost can end our vegetable gardening efforts any time after mid August. To jump the season, many gardeners use greenhouses or buy ready-made plants. Since zucchini or courgette plants (Cucurbita) sprout rapidly, grow quickly, and begin producing in roughly 40 to 50 days, the growing season comes to an end long before having to worry about powdery mildew (Sphgerotheca fuliginea).
This year, I decided to buy ready-made plants to make my gardening efforts easier – hoping for a bigger harvest before the frost hit. Big mistake. It’s been a relatively cool summer with temperatures in the 80s and lots of humidity due to more-than-average rainfall. While zucchini plants do well in spring and fall-type temperatures, they are more prone to powdery mildew when the humidity is high. Combine older plants with damp weather and you get a fatal fungus that spreads quickly throughout the garden.
What is Powdery Mildew?
Powdery mildew is a fungal disease that affects plants belonging to the Cucurbita pepo family; vegetables like:
- zucchini or courgette and other squashes
- pumpkins
- melons
- gourds
But it can also affect:
- cucumbers
- peas
- apples
- grapes
It’s a white, powdery-looking fungus that grows in a cobwebbed pattern over the top of the leaves; but can also be seen on the stems and flowers. More likely to occur during hot, humid conditions such as that experienced in late summer, most gardeners only have to contend with it when the season is about to close. At that time, you can just pull up the plants, or cut off the infected leaves when they first appear, to keep the fungus from spreading to other plants.
However, if left untreated, the leaves will curl, turn yellow, wilt, and die within only a few days. Sometimes, though weakened, the plant will try to survive by sending up new shoots and leaves, but that new growth will generally be stunted. Overall, the plant’s life will be shortened, but if it infects the rest of your garden, your gardening efforts and production can be seriously hindered.
Preventing Powdery Mildew on Zucchini Plants
Zucchini plants need a well-drained, airy place, so don’t plant them too close together. They need lots of air circulation and complete sunshine, not a damp, shady spot. Mulching the ground at the base of the plant will help keep the fungus spores in the dirt from getting on the leaves. Try not to get water on the leaves either, if you can help it. Zucchini leaves need to stay as dry as possible. So water the plants from the bottom – either by hand or with a drip system. Make sure you cut off any infected leaves as soon as you see the mildew appear on them.
Organic or Natural Fungus Control
While spraying with a fungicide is also an option, many gardeners are turning to a more organic or natural form of fungus and pest control. For powdery mildew, the gardener has several options:
Neem oil: If caught early enough, when plants are small or when mildew is just starting to get a foot hold, spraying your zucchini plants with Neem oil works well.
Chamomile tea: If steeped for at least 10 minutes, and used on zucchini plants when they are young or when the mildew is just starting, Chamomile tea makes a mild but effective fungicide.
Baking soda: Recommended in Organic Gardening magazine back in 1985, using baking soda against mildew isn’t new. Back then, the recommendation was only 1/4 ounce per gallon of water – about 1/2 of a tablespoon. Gardeners today recommend more. Try using 1 to 2 tablespoons added to a gallon of any insecticidal soap recipe. You can also use baking soda in combination with any pest control recipe that contains something sticky like vegetable oil. You want the soda to stick to the leaves, where it will act like a fungicide.
Skim milk: The effectiveness of cow’s milk against powdery mildew was scientifically tested in 1999. Many gardeners use it as a preventative, but it still works well if you begin spraying it on the leaves as soon as mildew appears. Recommended concentration is about 10 percent: that’s 1 part milk to 9 parts water. The reason why skim milk was used in the study was due to the odor the fat in the milk might cause as it breaks down. However, several gardeners on various gardening forums have shared that 2% milk did not cause an odor, and also worked well for them.
Keep on Top of Powdery Mildew for a Great Crop Harvest
While powdery mildew generally attacks zucchini plants and other squashes later in the season, a wet summer combined with store-purchased plants can hurry the process. If your garden is basically through producing, the easiest way to get rid of the mildew is to just pull up the affected plants and toss them onto your compost pile. The compost heat will take care of the problem. If your garden is young, there are many organic and sustainable methods that can help you keep your garden healthy. Above all, don’t ignore the problem. Not only will it cause the affected zucchini or courgette plant to wither and die, but it can also destroy the rest of your garden.
Sources
Crop Protection, Wagner Bettiol, “Effectiveness of cow’s milk against Zucchini squash powdery mildew (Sphgerotheca fuliginea) in greenhouse conditions,” 18:8, 489-492, September 1999.
Shepherd, Lizz, The Complete Guide to Growing Vegetables, Flowers, Fruits, and Herbs from Containers: Everything You Need to Know Explained Simply, Atlantic Publishing Group Inc., March 2011.
Smittle, Delilah, The Complete Idiot’s Guide to Year-Round Gardening, Alpha, February 2010.
Stewart, Robin, Robin Stewart’s Chemical Free Pest Control, Black Inc., 2002.
Vickie Ewell - Vickie has worked with autistic individuals for 9 years. She has celiac disease and specializes in gfcf living.
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