Impact of Verticutting on the Efficacy and Soil Activity of ALS-inhibiting Herbicides for Dallisgrass Control

Dallisgrass (Paspalum dilatatum Poir.) control with postemergence herbicides is inefficient and inconsistent from year to year. Control with acetolactate synthase (ALS)-inhibiting herbicides may be enhanced through root absorption, but herbicide movement through dense turfgrass canopies may be difficult. The objectives of this research were to evaluate the influence of verticutting on the postemergence control of dallisgrass and the presence of ALS-inhibiting herbicides within the soil profile. Long-term dallisgrass control [17 weeks after initial treatment (WAIT)] was enhanced in response to verticutting at one of two locations. This may be attributed to differences in turfgrass management (mowing height) before trial initiation that impacted dallisgrass carbohydrate content and herbicide absorption. However, dallis-grass control with certain herbicides was enhanced at the second location in response to verticutting at earlier rating dates. Thiencarbazone + foramsulfuron + halosulfuron (TFH) and trifloxysulfuron at 112 g.ha(-1) a.i. and carrier volume of 1628 L.ha(-1) (TRI High CV) following mowing + verticutting resulted in the greatest long-term control 17 WAIT at one of two trial locations, 86% and 85%, respectively. Greenhouse experiments confirmed that mowing + verticutting dallisgrass before treatment followed by irrigation led to an increase in herbicide presence within the soil profile, regardless of herbicide. Presence of TFH went from 6.4 to 8.2 mm, trifloxysulfuron at 28 g.ha(-1) a.i. and carrier volume of 407 L.ha(-1) went from 6.7 to 8.5 mm, and TRI High CV went from 8.6 to 11.8 mm.