Powdery mildew is easy to identify. It looks like white powder.
Powdery mildew on gerbera
An uninfected leaf
Powdery mildew is a fungal disease. Wet or humid conditions are conducive to powdery mildew infections. Treat it like you would other garden maladies. Soaps and oils can be effective, and fungicides can be called on if they list powdery mildew among their targets. Untreated, powdery mildew can damage leaves. Left unchecked, it can dramatically weaken bonsai.
Damage caused by powdery mildew
Sometimes the infections can look like white droplets.
Powdery mildew on calendula
Powdery mildew is less likely to strike conifers than it is broadleaf varieties. Japanese maples are quite susceptible, as are other deciduous varieties like stewartia or ume. If you have trouble with powdery mildew, moving the affected bonsai to a place that gets more light can help, as can ensuring the foliage doesn’t stay too wet. Systemic fungicides can help with difficult cases.
Interested in trying a “green” approach to managing powdery mildew? Try milk. I don’t have direct experience with this approach, but a 1:10 mixture of milk and water can be pretty effective. If you’ve tried this, do let us know how it worked!
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Many years ago I tried it on climbing Rose and it worked.
Powdery mildew is host specific, mildew on a Zucchini will not infect other plants. It overwinters on leaves stems and other garden litter. Best practice is to clean up and remove all litter from around infected plants. Removing infected leaves as you see them helps . Fungicides that do work are; sulfur and wettable coppers. Be careful with the systemics as some are toxic to invertebrates.
How about just old-fashioned gardening remedy, mouthwash. just dilute it down, and spray it on… It usually works for me
Tom Knoblauch says
Thanks for including organic methods in your blog. I don’t have mildew problems that i have tried this on, but have read about it. I do use raw milk and also unsulphured molasses to increase the bacteria in the soil, which is the food for other microorganisms which break down the nutrients.. I add them to my fertilized mix, and drench the soil. I also rinse out milk containers and pour this on my bonsai almost weekly.