COLUMBIA, S.C. — If it's August in the south, it's hot and it's humid. While many plants don't mind the humidity, there's a particular fungus that thrives in this weather called powdery mildew. It can destroy zucchini and squash crops for an entire season if the warning signs go unnoticed.
In Gandy's Garden here at WLTX, our zucchini plants went through most of the summer without any issues at all. I sprayed copper fungicide every one to two weeks to prevent fungal growth before it even showed signs of developing. This preventative measure worked, but after missing a few applications, powdery mildew quickly took over, and now I'm fighting an uphill battle.
I spoke with Clemson Extension Agent Jackie Johnson to clear up a few misconceptions about the fungus
There are multiple types of Powdery Mildew
Powdery Mildew describes a variety of different fungus. Each one grows on plant leaves stealing nutrients from plants and reducing their ability to photosynthesize. The result is reduced crop yield and when there is heavy infestations, death.
Powdery Mildew does not spread from one type of plant to another. The type of Powdery Mildew that uses Squash, Zucchini, and other members in the gourd family will not infest plants outside of that family. Some varieties are more resistant than others to powdery mildew. The Clemson Extension Agency has a list of plants that are more resistant to powdery mildew than others.
Powdery Mildew do not survive winter freezes.
This is good news because you can plant zucchini and squash in the same place each season without powdery mildew spores rising from the dirt. The bad side is that crop rotation will not help prevent powdery mildew. The fungus is carried each season from warmer parts of the world by the wind and by bugs and will infest plants year after year no matter where you plant them when temperatures reach their ideal 80-90F degree range.
Powdery Mildew can be prevented
Regular applications of copper fungicide will help slow or stop the growth of powdery mildew. Good airflow between plants will also discourage the fungus. The fungus prefers shady spots, although it will grow in full sun. If there's a heavy infestation, cut off the worst leaves.
I'll be following each of these tips to try and save the zucchini plants in Gandy's Garden, but with the humidity levels at their highest right now, it's going to be difficult to win against this garden issue!