VIEW ARTICLE

Ecology and Epidemiology

Infection of Leafy Spurge by Alternaria alternata and A. angustiovoidea in the Absence of Dew. Shaw- ming Yang, USDA-ARS, Foreign Disease-Weed Science Research Unit, Fort Detrick, Bldg. 1301, Frederick, MD 21702; D. R. Johnson(2), W. M. Dowler(3), and W. J. Connick, Jr.(4). (2)(3) USDA-ARS, Foreign Disease-Weed Science Research Unit, Fort Detrick, Bldg. 1301, Frederick, MD 21702; (3)Present address: Clemson University, 203 Long Hall, Clemson, SC 29634; (4)USDA-ARS, Southern Regional Research Center, New Orleans, LA 70179. Phytopathology 83:953-958. Accepted for publication 31 March 1993. 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, 1993. DOI: 10.1094/Phyto-83-953.

An invert emulsion carrier (IEC, water-in-oil type) was developed that could be applied easily with a garden sprayer (3.785 L with T-Jet 8002 nozzle) and that showed negligible phytotoxicity to leafy spurge. The IEC contained an oil phase and a water phase (1:1, v/v). The oil phase contained 20 ml of mineral oil, 2 ml of Myverol 18-99, 80 ml of Orchex 796, and 6 g of paraffin wax. The water phase contained 0.5 g of sucrose, 0.1 ml of Tween 20, and 100 ml of tap water. Eighty-five percent of conidia of Alternaria alternata and A. angustiovoidea germinated in the IEC in uncovered petri dishes in the greenhouse in the absence of dew at 21–25 C. However, less than 10% of conidia of A. alternata and 0% of that of A. angustiovoidea germinated in the aqueous sucrose solution under the same greenhouse conditions. When conidia of both Alternaria species were suspended in the IEC and sprayed onto leafy spurge, the plants were infected and killed in the absence of dew in growth chambers, greenhouse, and field plots. On the other hand, leafy spurge plants remained healthy under the same conditions when conidia of both Alternaria species were suspended in the aqueous sucrose solution and sprayed onto the plants.