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Effect of Crop Debris Management on Severity of Stemphylium Purple Spot of Asparagus. Dennis A. Johnson, Extension and Associate Plant Pathologist, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350. . Plant Dis. 74:413-415. Accepted for publication 29 December 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0413.

Asparagus debris from the previous seasonís fern was either incorporated into the soil or left on the soil surface in large plots in a commercial field. Severity of Stemphylium purple spot on spears was significantly reduced when debris was incorporated into the soil. Incorporation of debris into the soil was equally effective in late fall and in late winter. Ascospores and conidia of Pleospora herbarum on debris from the previous yearís fern growth served as primary inoculum. Volunteer asparagus seedlings became infected during the harvest season and may be important as a substrate for inoculum increase. They also may act as a bridge to carry inoculum through the harvest season to the time when the fern is allowed to regrow.