Fungal pathogens Microsphaeropsis amaranthi and Phomopsis amaranthicola as bioherbicides for pigweeds and waterhemp in pumpkin and soybean

Common waterhemp (Amaranthus rudis) and pigweeds ( Amaranthus spp. ) have become major problems in pumpkin ( Cucurbita pepo) and soybean (Glycine max) crops because they have evolved resistance to several herbicide families. The need for alternative weed control methods has increased since there are limited options for their control. The goal of this project was to develop two fungal pathogens (Microsphaeropsis amaranthi) and (Phomopsis amaranthicola) as agents for biological control of herbicide resistant waterhemp and pigweeds. Field trials were performed over two years, in Havana and Macomb IL, to evaluate the effectiveness of these organisms in irrigated and non-irrigated pumpkin and soybean plots. Treatments included a spore suspension of each fungal pathogen alone, a mixture of both pathogens, and a sequential treatment with either halosulfuron-methyl (SandeaRTM Herbicide) in pumpkin or glyphosate (RoundupRTM Herbicide) in soybean.;Effectiveness of the bioherbicides was determined by disease incidence, disease severity, disease severity index, % weed control, and weed biomass reduction. Results show a significant reduction in weed biomass when treated with one or both of the fungal organisms compared to the control treatment. Tank mixing M. amaranthi with halosulfuron-methyl shows potential to be a possible application technique. The development of these organisms as bioherbicides will improve crop yields by providing alternate opportunities for controlling problematic weeds. These fungal organisms show potential for use as a biological control method for herbicide resistant weeds in the genus Amaranthus.