Effects of green manures on Verticillium wilt of potato.

Two field studies were conducted to investigate the effects of green manure treatments on Verticillium wilt of potato (cv. Russet Burbank) caused by Verticillium dahliae. Each study involved the use of a sudangrass (Sorghum vulgare var. sudanense 'Monarch') green manure treatment and a fallow treatment for either 2 or 3 years prior to growing potato. In addition to sudangrass, comparisons also were made with several green manure treatments, including Austrian winter pea (Pisum sativum '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 sudangrass or corn ; after these treatments, yields were increased above all other treatments. Wilt was most severe when potato followed the fallow treatment and intermediate following rape, Austrian winter pea, oat, and rye. Wilt incidence was positively correlated with V. dahliae colonization in apical stems but was not significantly related to other pathogens (Pratylenchus neglectus, Colletotrichum coccodes, Rhizoctonia solani Ag-3) or to effects of green manure treatments on preplant nutritional effects of N, P, or K.