Evaluation of Bacillus spp. for managing late leaf spot and promoting yield in peanut production

Late leaf spot (LLS), caused by Nothopassalora personata, is a major disease that can lead to severe defoliation and yield loss in peanut. Currently, LLS management relies on conventional fungicides; however, emergence of fungicide resistance and environmental concerns create a need for complementary sustainable management strategies. This study evaluated Bacillus-based treatments, in-furrow or broadcast sprays, for their effects on LLS management and peanut yield in four field trials across three years in South Carolina. Commercial products containing strains D747 and QST713, two locally-isolated B. amyloliquefaciens strains, and phorate were applied in-furrow and followed by standard chlorothalonil programs. Additional experiments evaluated varying in-furrow application rates of commercial Bacillus products and foliar applications of Bacillus-based products in alternation with chlorothalonil. Chlorothalonil alone reduced LLS incidence in three trials. Adding in-furrow treatments did not further reduce disease incidence compared to chlorothalonil alone but consistently reduced it vs. the untreated control in all four trials. In-furrow treatments of D747, QST713, and phorate performed similarly; they significantly reduced defoliation and increased pod yield by 11.5-17.3% vs. chlorothalonil alone, while chlorothalonil alone did not improve yield over the untreated control. There was no significant difference between local strains and different examined rates of commercial Bacillus products in performance. In contrast, foliar applications of Bacillus products exhibited less efficacious disease suppression compared to chlorothalonil alone without yield advantage. These results demonstrate the potential of in-furrow applications of B. amyloliquefaciens for reducing LLS defoliation and promoting yield in peanut when integrated with conventional fungicide programs.