Control of Powdery Mildew on Hydrangea and Crapemyrtle with Antitranspirants

Abstract

Abstract Antitranspirants (‘Vapor Gard’ and ‘Wilt Pruf’) effectively controlled powdery mildew on Hydrangea macrophylla Thunb. and Lagerstroemia indica Nana. A 2% antitranspirant emulsion was sufficient to suppress the pathogen’s development without causing visible phytotoxic effect or plant growth inhibition. The antitranspirants were as effective, and in some cases more effective (‘Vapor Gard’), than the systmic triazole fungicide ‘Tilt’ in controlling the disease. Hydrangea and dwarf Lagerstroemia (crapemyrtle) are grown commercially as flowering pot plants. Disease-free plants are required. Powdery mildew (Erisiphe polygoni DC) often causes severe damage on greenhouse-grown hydrangea. This fungus usually appears 1st on the lower leaf surface, where it produces a white, loose, cottony mycelium. Yellowish or purple-white blotches with mycelium also can be observed on the upper surface of the leaf. When the disease develops under favorable environmental conditions, the symptoms cover not only the entire leaf surface but also the bud clusters and flowers (11). Various fungicides control powdery mildew under greenhouse conditions.