white powder? its mildew for sure!
powdery mildew is one of the most widespread and easily recognized plant diseases.
Powdery mildews are characterized by spots or patches of white to grayish, talcum-powder-like growth.
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1. A sulfur burner.... A device that slowly evaporates sulfur into the air that suppresses and kills the mildew.....
2. Keep that humidity down with a dehumidifier.... Humidity must be kept below 70%, especially during the night; levels over 80% will guarantee infection within 48 hrs.
Good ventilation and air circulation greatly reduces the risk of powdery mildew also....