Published online by Cambridge University Press: 12 June 2017
Field studies were conducted in 1996 and 1997 to determine the effects of RP-201772 and RP-201772 tank mixtures applied to emerged Zea mays. RP-201772 at 105 g ha−1 and tank-mixed metolachlor/benoxacor or atrazine were applied preemergence and to spike, 2-leaf, and 4-leaf Z. mays. Herbicide treatments over the four application timings provided greater than 90% Chenopodium album, Ambrosia artemisiifolia, Amaranthus retroflexus, and Abutilon theophrasti control. However, Setaria faberi control varied among years and application timings. Severe Z. mays injury, 70% and 40%, was observed when RP-201772 tank-mixed with metolachlor/benoxacor was applied to 2-leaf and 4-leaf Z. mays, respectively. Greenhouse studies confirmed Z. mays sensitivity from delayed applications of RP-201772 tank-mixed with metolachlor/benoxacor. Similarly, increased Z. mays injury was observed from postemergence applications of RP-201772 tank-mixed with acetochlor/MON-13900. Herbicide absorption, translocation, metabolism, and retention studies were conducted to determine the physiological basis for the observed Z. mays injury from delayed applications of the RP-201772 tank mixture with metolachlor/benoxacor. Metolachlor/benoxacor increased radiolabeled RP-201772 absorption when applied to spike, 2-leaf, and 4-leaf Z. mays. RP-201772 translocation and metabolism did not explain enhanced Z. mays injury. However, RP-201772 retention increased fivefold when metolachlor/benoxacor was present in the spray solution and applied to 2-leaf and 4-leaf Z. mays. Increased RP-201772 absorption and retention appeared to be the basis for Z. mays injury when tank-mixed with metolachlor/benoxacor and applied to emerged Z. mays.