Physiological Basis of Differential Sensitivity of Selected Graminaceous Species to Aminocyclopyrachlor

Abstract

Synthetic auxin herbicides are widely used in many grass systems due to their selective control of broadleaf weeds and safety to grass species. Aminocyclopyrachlor (ACPC) is a new synthetic auxin herbicide used for broadleaf weed control in pasture and rangeland systems. The fate of ACPC within treated grasses is not well understood. Research was conducted to establish the tolerance of four graminaceous species to ACPC application, observe the absorption, translocation, and metabolism of ACPC within treated grasses, and to determine if ACPC is exuded from the roots of treated grass species. Results indicate that tall fescue is the most tolerant of ACPC at rates that provide acceptable weed control. Bahiagrass and bermudagrass are marginally tolerant of ACPC and cogongrass is the most sensitive species. Tall fescue and bahiagrass absorbed more ACPC than bermudagrass and cogongrass, but cogongrass absorption is the most rapid and complete within 2 days after treatment (DAT). Cogongrass and bermudagrass moved the least herbicide out of the target area while bahiagrass and tall fescue translocated the most from the target area. No metabolism of ACPC was detected in any grass species out to 42 DAT. ACPC does exude through grass roots after foliar treatment into the surrounding environment in all species evaluated but the effect is minor and less than dicamba.