Military bases in the United States were mandated to reduce the amount of pesticide used to 50% of 1993 levels by 2000. Historically, 2,4-D was applied to control common sunflower, which establishes itself in disturbed soils and obstructs gunners' views of targets. A 25-ha lowland field in Camp Forsyth was selected to compare efficacy of alternative herbicides with that of 2,4-D low-volatile ester (LVE), with the goal of reducing the amount of herbicide applied by at least half. Site vegetation was mostly native tallgrass prairie dominated by warm-season C4 grasses (e.g., big bluestem, Indiangrass, little bluestem, and switchgrass) and including less abundant C3 species in the Asteraceae, Fabaceae, Brassicaceae, and other families. Initially, the site had a high population of common sunflower. All herbicide treatments from 3 yr of field trials were highly and equally effective at reducing common sunflower, decreasing stem density by 83 to100%. Treatments that offer substantial reductions in the amount of herbicide applied are chlorimuron (0.01 kg ae/ha), dicamba 2,4-D amine (0.07 kg ae/ha 0.20 kg ae/ha), clopyralid 2,4-D amine (0.06 kg ae/ha 0.28 kg ae/ha), 2,4-D LVE (0.56 kg ae/ha), and metsulfuron 2,4-D amine (0.002 kg ai/ha 0.28 kg ae/ha). Use of these herbicides at Ft. Riley would reduce total active ingredient applied by 73 to 99% and lower chemical costs for this particular use by as much as 88%.
Nomenclature: Chlorimuron; clopyralid; dicamba; metsulfuron; 2,4-D; common sunflower, Helianthus annuus L.
