Pathogenicity of Alternaria angustiovoidea on Leafy Spurge. Shaw- Ming Yang, Research Plant Pathologist, Foreign Disease-Weed Science Research Unit, USDA-ARS, Ft. Detrick, Bldg. 1301, Frederick, MD 21701. D. R. Johnson, and W. M. Dowler. Research Biologist, and Supervisory Plant Pathologist, Foreign Disease-Weed Science Research Unit, USDA-ARS, Ft. Detrick, Bldg. 1301, Frederick, MD 21701. Plant Dis. 74:601-604. Accepted for publication 3 January 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/PD-74-0601.

Experiments were conducted as a preclude to the use of Alternaria angustiovoidea as a biological control agent for leafy spurge (Euphorbia esula). A single dew period of at least 12 hr was needed for spores to cause slight infection (a few lesions) on inoculated leaves. To obtain severe infection (dead plants), a single dew period of at least 48 hr was needed. Two successive dew periods of up to 12 hr each did not increase infection over that of a single, 24-hr dew period. Twenty-two out of 25 collections of leafy spurge were susceptible to a single culture of A. angustiovoidea when they were incubated in dew chambers at 20–25 C for 48 hr after inoculation. Minor infection also occurred on globe artichoke, corn, cowpea, okra, safflower, and zinnia under the same conditions. A. angustiovoidea produced phytotoxins that caused chlorosis and wilting of leaves on cuttings of leafy spurge placed in the culture filtrate.