Anybody that has grown pumpkins and other squash plants should easily recognize powdery mildew, since it is very common in these large leafed plants.
By The original uploader was Agne27 at English Wikipedia
- USDA ARS, Public Domain, Link
It's fungal, non-fatal but very unsightly on bonsai. It is usually more likely to appear during the more humid times of the season. Humidity and moderate temperatures allow the fungus to thrive and spread rapidly. It may appear at first on the underside of leaves as small white powdery blotches but can eventually spread to cover the entire plant or everything which is above ground.
Aphids and other sucking insects are vectors for this fungus and often controlling them can assist greatly in reducing the outbreak of powdery mildew.
Increased air circulation, even resorting to fans if necessary can also reduce its prevalence among bonsai plants during susceptible periods.
Once it is present it can be treated with a systemic fungicide.
