PHACELIA, LANA WOOLLYPOD VETCH, AND AUSTRIAN WINTER PEA - 3 NEW COVERCROP HOSTS OF SCLEROTINIA MINOR IN CALIFORNIA

A 2-year field and greenhouse study identified three cover crops as ne w hosts for Sclerotinia minor. Pathogenicity was established by planti ng 4-week-old transplants of six cover crops and lettuce (Lactuca sati va) into sand amended with sclerotia. After 4 weeks of incubation in a greenhouse, phacelia (Phacelia tanacetifolia), Lana woollypod vetch ( Vicia dasycarpa), and Austrian winter pea (Pisum sativum L. subsp. arv ense) exhibited disease symptoms, as did lettuce, and S. minor was rei solated from the diseased cover crop plants. To assess susceptibility in a field situation, seven cover crop species, lettuce, and fallow tr eatments were placed for two consecutive years into randomized, replic ated field plots infested with sclerotia. In both the 1993 and 1994 ex periments, disease was observed on phacelia, Lana woollypod vetch, pur ple vetch (Vicia benghalensis), Austrian winter pea, and lettuce. Oils eed radish, barley, and fava bean did not become diseased. When lettuc e was planted after cover crop incorporation, phacelia, Lana woollypod vetch, and Austrian winter pea plots had significantly higher lettuce drop incidence than fallow plots in the first year. In the second yea r, only phacelia plots had significantly more lettuce drop. In a comme rcially planted lettuce field, lettuce drop incidence was significantl y higher 1 year in plots previously planted to phacelia. This is the f irst report of S. minor as a pathogen of phacelia, Lana woollypod vetc h, and Austrian winter pea cover crops in California.