William E. Chaney

Phacelia, Lana woollypod vetch, and Austrian winter pea : Three new cover crop hosts of Sclerotinia minor in California

A 2-year field and greenhouse study identified three cover crops as new hosts for Sclerotinia minor. Pathogenicity was established by planting 4-week-old transplants of six cover crops and lettuce (Lactuca sativa) 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. arvense) exhibited disease symptoms, as did lettuce, and S. minor was reisolated from the diseased cover crop plants. To assess susceptibility in a field situation, seven cover crop species, lettuce, and fallow treatments were placed for two consecutive years into randomized, replicated field plots infested with sclerotia. In both the 1993 and 1994 experiments, disease was observed on phacelia, Lana woollypod vetch, purple vetch (Vicia benghalensis), Austrian winter pea, and lettuce. Oilseed radish, barley, and fava bean did not become diseased. When lettuce 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 year, only phacelia plots had significantly more lettuce drop. In a commercially planted lettuce field, lettuce drop incidence was significantly higher 1 year in plots previously planted to phacelia. This is the first report of S. minor as a pathogen of phacelia, Lana woollypod vetch, and Austrian winter pea cover crops in California.