Mesotrione, Topramezone, and Amicarbazone Combinations for Postemergence Annual Bluegrass (Poa annua) Control

Abstract

Selective annual bluegrass (ABG) control with mesotrione is often inconsistent, and sequential applications might be required for complete control. The complementary nature ofp-hydroxyphenylpyruvate dioxygenase (HPPD)- and photosystem II (PSII)-inhibiting herbicides is well documented. The HPPD-inhibiting herbicide mesotrione and the PSII-inhibiting herbicide amicarbazone both have efficacy against annual bluegrass and safety on certain cool-season turfgrasses. Topramezone is a HPPD-inhibiting herbicide being investigated for use in turfgrass. Field and greenhouse experiments were conducted to examine single applications of topramezone and mesotrione alone or in combination with amicarbazone for POST ABG control in spring. In greenhouse experiments, the combination of mesotrione (280 g ai ha−1) and amicarbazone (75 g ai ha−1) controlled ABG 70% by 21 d after treatment, > 29% more than either herbicide applied alone; these combinations were determined to be synergistic. Amicarbazone combined with topramezone (14.5 g ai ha−1) provided < 10% ABG control and was not synergistic. When combined with mesotrione, increasing amicarbazone rate to 150 or 255 g ha−1did not increase ABG control compared to 75 g ha−1in field experiments. Combining mesotrione with amicarbazone resulted in a synergistic increase in POST ABG control at 1 and 2 wk after treatment (WAT). When applied alone or in combination with amicarbazone, increasing the mesotrione rate from 90 to 280 g ha−1increased efficacy on ABG in field experiments. The combination of mesotrione at 280 g ha−1and amicarbazone at 75 g ha−1provided > 90% ABG control in field experiments. Future research should focus on sequential applications of mesotrione–amicarbazone combinations for ABG control in locations where ABG is historically more difficult to control.