During the warm, rainy summer season our gardens thrive! As much as most of our plants enjoy the extra moisture, it can also bring some issues for more drought tolerant plants like zucchini, squash, cucumbers, and melons. Excess moisture can lead to powdery mildew. It forms on the leaves, and it starts as small white spots that can spread over the whole leaf leaving it brittle. Powdery mildew(PM) is highly contagious and can be easily spread across an entire plant. It can also travel between plants through the wind.
The root cause issue when powdery mildew enters the garden is too much moisture. The first step to help the garden is make sure you do what you can to prevent excess moisture from getting in. We can’t control the rain, but make sure your garden isn’t also watering on rainy days. Often times squash are the most susceptible, especially when we get more into summer and there is added stress with the heat. At the first sign of powdery mildew, it’s best to address it in the early stages. Prune off affected leaves first to prevent spreading and dispose of them immediately. If you’re still in the early stages, take off all leaves with white spots. If it’s begun to spread already, prune off all of the most affected leaves up to 50%. Once you’re done working on a plant, be sure to spray your tools and hands with alcohol to prevent spreading PM.
There are different organic methods for treating PM. One option is to use one tsp of Monterey Biofungicide concentrate, and one tsp of Prebiotech mixed well with water in a one gallon sprayer. Another recipe that can be even more effective is a mixture of one tsp potassium bicarbonate-food grade, one tsp vegetable oil, and a squirt of dawn soap in one liter of water in a sprayer. Mix very well so the potassium bicarbonate is dissolved, then thoroughly spray the base of the plant, stems, and tops and bottoms of leaves. Full coverage is very important to the success of the treatment. Keep in mind that if you are doing the formula that contains oil, only spray in the mornings or evening to prevent plant burning.
This treatment can be repeated every 5-7 days depending on the severity of the PM.
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