Diseases of onion and garlic (
Powdery mildew of garlic
Powdery mildew of garlic is caused by Oidiopsis sp. The disease was observed on mature plants in early summer of 1999 in Arizona (photo 1). It caused no apparent damage to cloves, but lesions on leaves were extensive. Powdery mildew of garlic has not been reported in the United States to our knowledge, but is probably closely related to the powdery mildew that has been reported on onion in California, Oidiopsis sicula. The sexual or perfect stage, Leveillula, was not found.
Powdery mildew on garlic causes light yellow lesions on leaves (photo 2) within which single spores (conidia) on clusters of stalks (conidiophores) emerge from stomatal openings. If disease appears on younger plants, applications of sulfur may be warranted. Sulfur should be applied as soon as disease is observed.
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February 10, 2003