Research report to the Oregon Processed Vegetable Commission
OSU Dept. of Botany and Plant Pathology
Sclerotinia sclerotiorum (causal agent of white mold) can cause serious economic losses in snap bean and produces sclerotia, which are long-lived, durable hyphal survival structures that can survive up to eight years between hosts. Gray mold (Botrytis sp.) can also infect bean, but usually occurs at very low levels in our fungicide trials. We evaluated the efficacy of fungicides in a 2-spray program on mold in snap bean '91G' planted in an experimental field on the OSU Botany Farm.. White mold was observed on 15% of the pods per plant in the nontreated control plots while gray mold averaged < 1 % pod incidence per plant. The percentage of infected pods > 2-in. in length and number of stems affected by white mold were lower in most of the fungicide treatments. The tank mix of Topsin + Rovral was numerically the best in controlling white mold on pods but was statistically equivalent to Omega and Cannonball. Treatment with Endura, Switch, Fontelis, or Regalia + Topsin were inferior compared to Topsin + Rovral at managing white mold on pods, but offered improvements in pod disease control compared to the nontreated plots, though Fontelis was associated with a high level of pod infections. The average number of white mold stem hits was lowest in Topsin + Rovral as well as Cannonball and one Omega treatment. The levels of gray mold on pods was overall low but Fontelis and Cannonball at the rates tested, appeared inferior to the other materials, except Switch, on gray mold. The number of healthy, marketable-size bean pods was greatest in the tank mix of Topsin + Rovral as well as Omega at the top rate while the lowest numbers were observed in the nontreated water control and Cannonball.