Effects of 2,4-D and atrazine on degraded Oklahoma grasslands

Abstract

Three field studies were conducted for 2 years on degraded grasslands to compare the effects of 2,4-D [(2,4-dichlorophenoxy) acetic acid] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] on weedy forbs and grass production. Atrazine was applied at 1.12 and 2.24 kg/ha in April and 2,4-D was applied at 0.56 and 1.12 kg/ha in May. One-half of all main plots were retreated the second year to compare 1 and 2 years of herbicide treatments. Major weedy forbs were heath aster (Aster ericoides L.), western ragweed (Ambrosia psilostachya D.C.), and lanceleaf ragweed (Ambrosia bidentata Michx.). Both density and standing crop of these major forb species were significantly reduced by the first year herbicide treatments. Atrazine was more effective on western ragweed and 2,4-D was more effective on heath aster and lanceleaf ragweed. Respraying with herbicides the second year did reduce forb density in a couple of instances, but had little effect on forb and grass standing crop. Grass standing crop in both years was similar after treatment with atrazine and 2,4-D. Herbicides increased grass standing crop by about 73% (1,070 kg/ha) the first year and by an average of about 68% (1,320 kg/ha) the second year.