Weed Efficacy in Warm-Season Turfgrass Using Canadian Bioherbicide Phoma Macrostoma.

Effective natural options for weed control in turfgrass systems have been limited.  Studies were conducted in warm-season turfgrass to evaluate efficacy of Canadian BioHerbicide, a granular biopesticide being developed for selective broadleaf weed control.  This product, produced from the solid fermentation of the fungus Phoma macrostoma on grain, is applied as a dry granular product to turfgrass.  Herbicidal activity from this product causes foliar bleaching and necrosis of susceptible broadleaf weeds.  Studies were carried out in Dallas and College Station, Texas during 2011 and 2012 to evaluate various formulations and product application rates for control of slender aster, dandelion, and false dandelion populations.  Studies were conducted on irrigated stands of St. Augustinegrass, ‘Tifway 419’ bermudagrass, and common bermudagrass.  Applications in 2011 were split-applied on days 0 and 28.  Although temperatures (23-30 ºC) during the study period were considerably higher than that required for optimal activity of the fungus (10-25 °C), some of the formulations provided statistically similar dandelion control (80-87%) to metsulfuron (98%) application, with a rate-dependent response occurring with both formulations.  The highest application rates of both formulations provided slender aster control of 85 and 80%, significantly less than that provided by Ortho Weed-B-Gon at 2 pt. A^-1, when evaluated 30 DAT after a single application.  Sequential applications failed to improve activity, likely due to extremely high temperatures at the time.  In 2012, single applications were applied to false dandelion and slender aster.  At 28 DAT, the highest application rate provided 97% control of false dandelion, but thereafter weed populations declined in all treatments due to elevated temperatures.  The highest application rates provided 68 and 94% control of slender aster by 55 DAT, significantly higher than that of Ortho Weed-B-Gon at 2 pt. A^-1.  Phytotoxicity was not observed in any turfgrass species, regardless of application rate, during the studies.