Biological Control of Damping-Off of Snapbeans Caused by Sclerotium rolfsii in the Greenhouse and Field with Formulations of Gliocladium virens

The effect of Pyrax dust (pyrax), alginate pellets, and activated vermiculite/bran (VBB) formulations containing biomass of the biocontrol fungus Gliocladium virens (G1-3) on pre- and postemergence damping-off of snapbeans (Phaseolus vulgaris) caused by Sclerotium rolfsii was determined from greenhouse and field trials. The ability of these formulations to reduce germination of scierotia of S. rolfsii was also evaluated. In the greenhouse, pyrax/biomass and alginate pellet formulations, which provided as little as 1.5 × 103 colony forming units (cfu) of G1-3 per gram of soil, significantly increased plant stand in pathogen-infested soil over that in the untreated control. Formulations which provided 3.0 × 103 cfu of G1-3 per gram of soil gave stands (>80%) comparable to that in noninfested, pathogen-free soil. In order to achieve similar results with activated VBB, soil had to be amended with a formulation that provided at least 2.3 × 104 cfu of G1-3 per gram of soil. All three formulations reduced the germination of sclerotia of S. rolfsii in loamy sand and loam soils in the greenhouse. In loamy sand amended with pyrax/biomass, alginate pellets, and activated VBB, the scierotial germination was inversely correlated (r = −0.93, −0.94, and −0.79, respectively) with snapbean stand in the greenhouse. However, a higher rate of activated VBB than the other two formulations was necessary to achieve a comparable reduction in sclerotial germination. Over a 2-year field study, all three formulations added to soil to provide 103 to 104 cfu of G1-3 per gram significantly prevented damping-off, but no treatment yielded a plant stand similar to that in noninfested soil (73-85%) after 35 days of growth. Pyrax/biomass, alginate pellets, and activated VBB gave final stands of 59 to 73, 57 to 71, and 62 to 77%, respectively. The addition of the formulations to loamy sand in the field resulted in a 1000-fold increase in propagule numbers of G1-3 within 11 days of application.