Selectivity and Soil Persistence of Certain Herbicides Used on Perennial Forage Grasses

Abstract

AbstractSeveral herbicides were applied in the field to the cool‐season grass smooth brome (Bromus inermis Leyss.) and to three warm‐season grasses, sideoats grama [Bouteloua curtipendula (Michx.) Torr.], switchgrass (Panicum virgatum L.) and indiangrass [Sorghastrum nutans (L.) Nash] to evaluate herbicide persistence in soils supporting each of these perennial forage grasses. Herbicides were applied once and the soil was sampled to a depth of 91 cm, 4 and 16 months after application. Bioassays, with soybeans [Glycine max (L.) Merr.] as the test crop, were conducted in the greenhouse to determine the location of the herbicides in the soil profile.Most herbicide residues 4 or 16 months after application were located in the 0‐ to 8‐cm soil depth. Only bromacil (5‐bromo‐3‐sec‐butyl‐6‐methyluracil), karbutilate [tert‐butylcarbamic acid ester with 3‐(m‐hydroxyphenyl)‐1,1‐dimethylurea] or terbacil (3‐tert‐butyl‐5‐chloro‐6‐methyluracil) at high rates depressed soybean growth in soil from the 8‐ to 15‐cm depth. Four months after herbicide application, a slight increase in soybean growth was evident in soil from the 15‐ to 30‐cm depth where bromacil, karbutilate, or terbacil had been applied to bromegrass.Germination of seed harvested from each grass was not affected by herbicide treatments.