ABSTRACT
Field studies were conducted to evaluate the effectiveness of Sporidesmium sclerotivorum to control Sclerotinia stem rot of soybean (SSR) at Ames, Humboldt, and Kanawha, IA, between 1996 and 1998. Experimental plots (3 × 3 m) were infested with S. sclerotivorum macroconidia once at a rate of 0, 2, or 20 spores per cm2 in the fall of 1995 or the spring of 1996, under two crop rotation schemes. A randomized complete block design with four replications in each location was used. Plots infested with 20 spores per cm2 had 62% less SSR (P = 0.05) than control plots at Humboldt in 1996. No differences were detected between fall and spring applications. In 1998, plots treated with either 2 or 20 spores per cm2 had 51 to 63% less SSR (P = 0.05) than control plots at Ames and Kanawha. In 1998, SSR was completely suppressed in all plots at Humboldt, while the commercial field surrounding the experimental plots had 17% SSR. S. sclerotivorum was retrieved from all infested plots at all locations 2 years after infestation with sclerotia of Sclerotinia sclerotiorum as bait. At Humboldt, S. sclerotivorum was also retrieved from control plots. Two larger plots (10 × 10 m) were infested with 20 or 100 spores per cm2 in the fall of 1996 or spring of 1997 in six commercial fields. SSR incidence, which was measured in transects up to 20 m from the infested area at 5-m intervals, was reduced 56 to 100% (P = 0.05) in four fields compared with the surrounding uninfested areas in the commercial fields. Dispersal of the control agent was evident by the fact that SSR incidence gradually increased from the edge of the infested macroplots up to about 10 m into noninoculated areas of the commercial field. This paper constitutes the first report describing the biocontrol of a disease on field crops that may be employed economically.
