Phytophthora blight, caused by Phytophthora capsici, is the most economically
significant disease of bell pepper in the US. Over the past several decades, isolates of
Phytophthora capsici exhibiting resistance to mefenoxam have been reported. This threat of
resistance coupled with an increased market for organically grown crops has led to interest in
disease management through biological control. In this project, we evaluated a strain
(AFS032321) of Bacillus subtilis that is antagonistic in vitro to Phytophthora spp. on
Phytophthora blight of bell pepper in greenhouse and field conditions. A wettable powder
formulation of the strain was applied as a soil drench at transplant prior to pathogen inoculation.
In the greenhouse, 30 and 40 lb/acre applications of B. subtilis strain AFS032321 significantly
reduced disease severity and the area under the disease progress curve (AUDPC) from 30.7 in
controls to 20.5 and 15.5, respectively. In the field, B. subtilis strain AFS032321 significantly
reduced disease comparable to the labeled rate of mefenoxam on a susceptible pepper variety
“Red Knight” and AUDPC from 37.9 in the control to 28.7 and 25.6 respectively. Ongoing
research includes investigating timing of biocontrol application and the effect of soil type on
management efficacy and the potential of B. subtilis strain AFS032321 to manage mefenoxam-
resistant isolates of P. capsici.