UTILITY OF AMINOCYCLOPYRACHLOR FOR CONTROL OF HORSENETTLE AND TALL IRONWEED IN COOL-SEASON GRASS PASTURES

Previous research has shown that management of horsenettle (Solanum carolinense) and tall ironweed (Vernonia gigantea) in cool-season grass pastures and hayfields is difficult. Therefore, research was conducted at Alcoa, Fork Creek, Greenback, Maynardville, and Pulaski, Tennessee, and at London, Kentucky, in 2010 and 2011 to examine efficacy of aminocyclopyrachlor on these two perennial weeds. Research was conducted on naturally-occurring infestations of each weed. Treatments were: aminocyclopyrachlor (49 g ai/ha) with and without 2,4-D amine (371 g ai/ha), aminocyclopyrachlor (98 g ai/ha) with and without 2,4-D amine (742 g ai/ha), and aminopyralid (88 g ai/ha). Treatments were applied at three postemergent (POST) timings to horsenettle, which corresponded to horsenettle in a vegetative (EPOST), flowering (MPOST), or fruit-setting (LPOST) growth stage. Treatments were applied at two POST timings to tall ironweed, when ironweed was either vegetative (EPOST) or flowering (LPOST). Analysis of this RCB was conducted utilizing ANOVA in SAS. Means were separated using Student-Newman-Keuls.

Treatment effects were found to be significant for visual weed control, weed density, and height (P<.05). Year-after control of horsenettle was found to be as high as 81% with a LPOST application of aminocyclopyrachlor at 98 g ai/ha with 2,4-D at 742 g ai/ha. Equivalent control was achieved with aminocyclopyrachlor at other rates applied MPOST and LPOST, and with aminopyralid at 88 g ai/ha applied MPOST. Tall ironweed was controlled 99% 1 YAT with aminocyclopyrachlor at either timing at rates as low as 49 g ai/ha, while aminopyralid applied LPOST at 88 g ai/ha provided 96% control. Both aminocyclopyrachlor and aminopyralid were found to significantly reduce horsenettle and tall ironweed biomass the following year.

The best year-after control of horsenettle (~80%) was achieved with aminocyclopyrachlor LPOST and aminopyralid applied MPOST. The best year-after control of tall ironweed (>96%) resulted from LPOST applications of aminocyclopyrachlor or aminopyralid. Therefore, a late-summer application, when there is adequate soil moisture, would be optimal for control of horsenettle and tall ironweed with aminocyclopyrachlor. A dose of at least 98 g ai/ha would be recommended to control horsenettle; tall ironweed could be controlled at rates as low as 49 g ai/ha.