Phoma macrostoma Montagne is a fungus being developed as a natural herbicide for selective broadleaf weed control. The solid fermentation of P. macrostoma on grain produces a product that is applied as a dry granule. Herbicidal activity is characterized by foliar bleaching and necrosis of susceptible broadleaf weeds. Previous research with this product was limited to cool-season climates, and information is limited regarding appropriate application rates or efficacy at higher temperatures and weeds associated with warm-season turf. Spectrum of weed control is still being explored, most recently in Texas. Multiple years of field and greenhouse research were conducted in College Station, TX, to evaluate the efficacy of P. macrostoma for broadleaf weed control. Field studies showed that P. macrostoma was effective at controlling slender aster (Aster subulatus var. ligulatus Shinners), with higher application rates providing 89 to 94% control. Field studies also showed that P. macrostoma was able to maintain efficacy at high temperatures, with maximum temperatures of 41?C. Greenhouse studies indicated a variable weed control spectrum, with P. macrostoma providing excellent control of dandelion (Taraxacum officinale Weber ex F.H. Wigg.), but little to no activity on other weeds including common mallow (Malva neglecta Wallr.) and common purslane (Portulaca oleracea L.). Growth chamber studies indicate that environmental factors such as temperature and moisture affect the efficacy by P. macrostoma, and culturalpractices such as nitrogen fertilization coupled with P. macrostoma application may enhance herbicidal activity. Over the course of this research, no injury was observed on any species of warm-season turfgrass, making P. macrostoma a promising biorational option for natural weed control in lawns.
