Peanut Response to Soil and Foliar Applications of Imazapyr

Georgia leads the nation in both pine tree (Pinus spp.) timber volume and peanut (Arachis hypogaea L.) ha harvested annually. Off-target movement of pine forest herbicides into peanut fields can occur from aerial applications. Research was conducted from 2020-2022 in Ty Ty, Georgia to determine peanut response to imazapyr from preemergence (PRE) and postemergence (POST) applications. Imazapyr was applied to peanut (cv. Georgia-06G) at the following timings and rates: PRE (1 day after planting) (DAP), 30 DAP, and 60 DAP; and 420 (1X, manufacturers suggested use rate), 84 (1/5X), 42 (1/10X) and 4.2 g ai/ha (1/100X). Peanut density was not reduced by any PRE application of imazapyr. Significant stunting, chlorosis, and reductions in peanut plant height and width occurred from 420 g ai/ha, regardless of application timing. Peanut was more susceptible to imazapyr injury from PRE applications, as peanut heights were reduced by rates ≥ 42 g ai/ha and peanut widths were reduced by rates ≥ 84 g ai/ha. With POST applications, only 420 g ai/ha resulted in plant height and width reductions of 66% and 48% when applied 30 DAP. Peanut treated at 60 DAP had 30% and 57% height reductions with rates of 84 and 420 g ai/ha, respectively. The 420 g ai/ha rate resulted in yield losses of 79%, 66%, and 56% when applied PRE, 30 DAP, and 60 DAP, respectively. PRE applications of imazapyr at 42 or 84 g ai/ha resulted in 31% and 59% yield reductions, respectively. These results suggest that peanut should not be planted to fields exposed to full rates of imazapyr until rates decline to < 42 g ai/ha (~three half-lives or 426 d). Peanut exposed to POST applied imazapyr ≤ 84 g ai/ha (1/5X) during the growing season should not result in significant yield losses.