Evaluation of Weed Control of Phoma Macrostoma for Use in Warm-Season Turf.

Effective natural options for weed control in turfgrass systems have been limited.  Phoma macrostoma 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 from this product causes foliar bleaching and necrosis of susceptible broadleaf weeds.  Previous research with this product is limited to cool-season climates, and information is limited on 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.  Field and greenhouse studies were conducted in Dallas and College Station, TX from 2011 to 2013 to evaluate the efficacy of P. macrostoma for broadleaf weed control.  Field studies were conducted on irrigated stands of St. Augustinegrass, hybrid bermudagrass, and common bermudagrass.   2011 applications were split-applied on days 0 and 28, with the highest rates of both formulations providing up to 87% control of dandelion and 95% control of slender aster.  In 2012, single applications were applied to false dandelion and slender aster, with the highest rate providing 97% control of false dandelion 28 days after treatment (DAT) and up to 94% control of slender aster 55 DAT.  In greenhouse trials the highest application rate provided between 95 to 100% control of dandelion, and up to 70 to 75% control of slender aster and annual sowthistle, respectively.  Though chlorosis was visible on California burclover, control was limited, and   P. macrostoma had no activity on common purslane, common mallow, or yellow woodsorrel.  Phytotoxicity was not observed following application to any species of turf, regardless of application rate.