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My neighbor gets home from work at about the same time I do. He nods his head and hollers, “Hot enough for ya?” I grin, and then roll my eyes. At least I can go to a nice cool house. Our garden plants can’t.
Powdery mildew loves hot humid weather and can be a problem—particularly this time of year when our young vegetable plants are much bigger than they were when we planted them and there is less air circulation around them. (This is why I always try to space my plants as far apart as I can.)
Cucurbits (cucumber family members) are particularly vulnerable so look for little white powdery spots to appear on the foliage. Eventually, those spots will grow to cover most of the leaf. Powdery mildew thrives on new tender growth, so if it shows up, avoid applying fertilizer until you have gotten it under control.
Believe it or not, a study at the University of Connecticut found that a mixture of 40% milk and 60% water as a spray is fairly effective when powdery mildew first appears. Neem oil can also be used, but be sure to spray when temperatures are below 90 degrees to avoid damage.
Some vegetables will abort their flowers when temperatures reach into the 90’s. Other vegetables—tomatoes, pepper, and eggplants, in particular—will have trouble setting fruit because heat and humidity can damage the pollen.
While tomatoes are self-pollinating, when the weather is hot and humid, it renders the pollen “sticky” so that the wind can’t dislodge it. Lack of air circulation makes it worse. On the other hand, if daytime temperatures are above 86° and nighttime temperatures fail to fall below 75°, this can render the pollen useless. All is not lost, however, keep your plants watered and fed and they will begin producing viable pollen as soon as the weather is more to their liking.
If heat persists, you may even want to invest in light shade cloth to give your plants a break—be sure to suspend it about a foot or so above your plants to allow plenty of air circulation. And I probably would not use it if I had a problem with powdery mildew.
Keep your garden weeded (yeah, it’s a lot of fun in the heat). Plants, already struggling with the heat, shouldn’t have to compete for water or nutrients.
Last, but certainly not least, keep YOURSELF cool. Garden early morning or late evening when it has cooled a bit. Keep well hydrated.