Suppression of Sclerotinia stem rot of soybean by lactofen herbicide treatment

Severity of Sclerotinia stem rot of soybean after treatment with lactofen ( Cobra) and other herbicides was assessed in field experiments conducted in Michigan from 1995 to 1997. At sites where disease pressure was high, disea se severity was reduced 40 to 60% compared with controls when lactofen was applied at the V3 (1995 and 1996) or R1 (1997) growth stages. Corresponding seed yields were unchanged or up to 20% greater when lactofen was applied at the R1 stage in 1997. Disease severity was not reduced by lactofen treat ments in years and at sites where disease pressure was low to medium, and c orresponding yields often were reduced by approximate to 10%. High levels o f glyceollin accumulated in lactofen-injured leaves collected from field pl ots in 1996 and 1997. High glyceollin content in lactofen-treated leaves wa s associated with significant reductions in lesion size when leaves were ch allenge-inoculated with Sclerotinia sclerotiorum.