Cogongrass Control with Aminocyclopyrachlor in Pastures

Abstract

Aminocyclopyrachlor is a new pyrimidine carboxylic acid herbicide that controls a wide range of pasture weeds. Recent research has shown that it may also have some activity on cogongrass which is an increasing problem in pastures and hayfields. Since current herbicide options for cogongrass control in pastures are non-selective, any new selective tools would be useful. We evaluated aminocyclopyrachlor applied at fall or spring timings against glyphosate and imazapyr for cogongrass rhizome, shoot, and seedhead control. At 12 months after treatment (MAT), aminocyclopyrachlor reduced rhizome biomass by 28% while glyphosate and imazapyr reduced rhizome biomass by 77 and 80%, respectively. Both fall and spring treatment timings resulted in a similar pattern of good spring control of shoot growth and flowering but new shoot growth occurred during the summer and fall. Additional aminocyclopyrachlor dose response studies indicated that repeated fall treatments inhibited cogongrass spring flowering at low rates but did not effectively control shoots even at high rates. These results indicate that aminocyclopyrachlor does provide short-term vegetative control of cogongrass and can strongly inhibit flowering the year after treatment. This ability to prevent cogongrass flowering while suppressing vegetative cover may allow aminocyclopyrachlor to be useful in certain pasture situations.