Goosegrass Control and Turfgrass Injury Following Metribuzin and Topramezone Application with Immediate Irrigation

Abstract

Goosegrass (Eleusine indica L. Gaertn.) is a problematic C4 weedy grass species, occurring in the warmer regions of the world where it is difficult to selectively control without injuring the turfgrass. Furthermore, control efficacy is affected by plant maturity. End-user options for satisfactory goosegrass control has decreased; thus, the need for developing management techniques to improve the selectivity of POST goosegrass control options in turfgrass systems is ever increasing. One possible means of providing control, yet maintaining turf quality is immediately incorporating applied products via irrigation. Greenhouse and field trials were conducted in Pickens County, SC, with the objectives of 1) evaluating turfgrass injury following use of POST goosegrass control options; 2) assessing if irrigating (0.6 cm) immediately following the herbicide application reduces injury of ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy]; and 3) determining if immediate irrigation influences goosegrass control at one- to three-tiller and mature growth stage. Following the application of herbicide treatments, irrigation was applied (+) or not applied (−). Treatments included the following: control (+/− irrigation); topramezone at 12.3 g a.i./ha (+/− irrigation); metribuzin at 420 g a.i./ha (+/− irrigation); and topramezone plus metribuzin (+/− irrigation) at 12.3 and 420 g a.i./ha. Irrigation treatment had minimum effect on greenhouse-grown goosegrass biomass, all treatments provided >85% control of 1- to 3-tiller goosegrass plants. However, control for mature plants was <50% for topramezone- and 60% to 70% for metribuzin-containing treatments. In field studies, at 1 week after treatment (WAT), the irrigated metribuzin and topramezone plus metribuzin had ≈37% and ≈16%, respectively, less goosegrass control vs. nonirrigated treatments. At 2WAT, irrigated metribuzin and irrigated topramezone plus metribuzin–treated plots, had ≈50% less mature goosegrass control vs. nonirrigated treatments. Irrigated herbicide treatments, however, experienced ≈23% less turfgrass injury at this time. At 4 WAT, irrigated metribuzin- and irrigated topramezone plus metribuzin–treated plots experienced reduced mature goosegrass control by ≈65% and ≈59%, respectively. Overall, incorporating POST herbicide applications via 0.6 cm of irrigation reduced turfgrass injury by at least 20% for all herbicide treatments, while maintaining goosegrass control.