White growth, often with a yellow margin, on the surface of leaves and stems. Leaves eventually turn brown, die and fall off the plant. Symptoms typically appear first on the plant's lower leaves and progress upward. Lesions do not appear on fruit, but fruit may suffer from sunscald due to defoliation in severe cases. Warm, humid weather favors development of the disease. Spores are carried by the wind, and entire plantings may be quickly infected. Note: This disease appeared for the first time in tomato fields and home gardens throughout North America in 1996.
If tomato plants already show symptoms of tomato powdery mildew, spray Bacillus subtilis to boost plants' natural defenses and repeat at 7-day intervals, as needed, to control the disease. If powdery mildew has been a problem in the past, use the biofungicide as a preventative; begin spraying foliage when conditions favor disease and repeat weekly until harvest. We recommend Plant Guardian™ Biofungicide Wettable Powder.