EFFECTS OF GREEN MANURES ON VERTICILLIUM WILT OF POTATO

Two field studies were conducted to investigate the effects of green m anure treatments on Verticillium wilt of potato (cv. Russet Burbank) c aused by Verticillium dahliae. Each study involved the use of a sudan grass (Sorghum vulgare var. sudanense 'Monarch') green manure treat me nt and a fallow treatment for either 2 or 3 years prior to growing pot ato. In addition to sudangrass, comparisons also were made with severa l green manure treatments, including Austrian winter pea (Pisum sativu m 'Austrian winter'), two cultivars of rape (Brassica napus var. napus 'Dwarf Essex' and 'Bridger'), rye (Secale cereale), oat (Avena sativa 'Monida'), and corn (Zea mays 'Jubilee'). Verticillium wilt of potato was best controlled after green manure treatments of either sudangras s or corn; after these treatments, yields were increased above all oth er treatments. Wilt was most severe when potato followed the fallow tr eatment and intermediate following rape, Austrian winter pea, oat, and rye. Wilt incidence was positively correlated with V. dahliae coloniz ation in apical stems but was not significantly related to other patho gens (Pratylenchus neglectus, Colletotrichum coccodes, Rhizoctonia sol ani Ag-3) or to effects of green manure treatments on preplant nutriti onal effects of N, P, or K.