The relationship of goosegrass (Eleusine indica) stage of growth to quinclorac tolerance

Goosegrass is considered tolerant to quinclorac. The purpose of this study was to determine whether there was a stage of growth at which it was susceptible. Stage of growth studies with goosegrass were conducted that evaluated quinclorac activity at rates of 0, 1, 2, 4, 8, and 16 kg ai/ha applied with 1% (v/v) Merge spray adjuvant. Quinclorac application stages evaluated included preemergence and one- to two-leaf, four- to five-leaf, and one- to two-tiller stage. The effects of root uptake from posternergence applications were also evaluated by comparing treatments with and without a vermiculite soil barrier. Goosegrass was more susceptible to quinclorac when applied preemergence or early postemergence at the one- to two-leaf stage than at later more mature stages. The importance of root uptake on quinclorac activity was also observed, particularly at the four- to five-leaf stage, where the dose required to reduce growth 50% (GR(50)) in the absence of the soil barrier was 3.4 kg/ha vs. 16 kg/ha in the presence of a barrier. At the most advanced growth stage of one to two tillers, calculated GR(50) values were greater than 16 kg/ha whether a soil barrier was present or not. The lowest calculated GR(50) value of 2.7 kg/ha for the one- to two-leaf stage with no soil barrier was still approximately 3.5 times higher than the maximum labeled rate for turfgrass.