Triclopyr Reduces Foliar Bleaching from Mesotrione and Enhances Efficacy for Smooth Crabgrass Control by Altering Uptake and Translocation

Turfgrass managers can reduce foliar bleaching of smooth crabgrass from mesotrione by tank-mixing triclopyr ester with applications. These tank mixtures also have potential to enhance smooth crabgrass control compared to mesotrione alone. The objectives of this research were to evaluate the influence of triclopyr on the efficacy, absorption, and translocation of mesotrione in multitiller smooth crabgrass. In field experiments, tank-mixing triclopyr at 560 or 1,120 g ae ha⁻¹ with mesotrione at 140 g ai ha⁻¹ applied sequentially or at 280 g ha⁻¹ applied singly provided excellent control (> 90%) of multitiller smooth crabgrass in tall fescue. These treatments were more effective than mesotrione alone and fenoxaprop at 195 g ai ha⁻¹ that averaged 66 and 81% control after 6 wk, respectively. Mesotrione alone at 280 g ha⁻¹ bleached smooth crabgrass 53% at 2 wk after initial treatment (WAIT), and was 14% greater than the 140 g ha⁻¹ treatment. Sequential treatments of the low mesotrione rate bleached smooth crabgrass 16 to 22% from 3 to 5 WAIT. Triclopyr tank mixtures reduced smooth crabgrass bleaching from mesotrione on all dates to < 5%. Tall fescue injury was not detected at any evaluation date. In laboratory experiments, smooth crabgrass reached peak foliar absorption of ¹⁴C-mesotrione at 24 and 168 h after treatment (HAT; 23% and 15%) when mesotrione was applied with triclopyr at 1,120 and 0 g ha⁻¹, respectively. Triclopyr reduced translocation of radioactivity 12% at 72 and 168 HAT, compared to ¹⁴C-mesotrione alone. Enhanced foliar uptake of mesotrione from triclopyr tank mixtures might improve control of multitiller smooth crabgrass compared to mesotrione alone. Reduced foliar bleaching from triclopyr is associated with less translocation of mesotrione or derivatives in smooth crabgrass.Nomenclature: Smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb ex. Muhl.; tall fescue, Festuca arundinacea Shreb. ‘Titan'.