Weed control andZea maystolerance as affected by timing of RP-201772 application

Field studies were conducted in 1996 and 1997 to determine the effects of RP-201772 and RP-201772 tank mixtures applied to emergedZea mays.RP-201772 at 105 g ha−1and tank-mixed metolachlor/benoxacor or atrazine were applied preemergence and to spike, 2-leaf, and 4-leafZ. mays.Herbicide treatments over the four application timings provided greater than 90%Chenopodium album, Ambrosia artemisiifolia, Amaranthus retroflexus, andAbutilon theophrasticontrol. However,Setaria fabericontrol varied among years and application timings. SevereZ. maysinjury, 70% and 40%, was observed when RP-201772 tank-mixed with metolachlor/benoxacor was applied to 2-leaf and 4-leafZ. mays, respectively. Greenhouse studies confirmedZ. mayssensitivity from delayed applications of RP-201772 tank-mixed with metolachlor/benoxacor. Similarly, increasedZ. maysinjury 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 observedZ. maysinjury 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-leafZ. mays.RP-201772 translocation and metabolism did not explain enhancedZ. maysinjury. However, RP-201772 retention increased fivefold when metolachlor/benoxacor was present in the spray solution and applied to 2-leaf and 4-leafZ. mays.Increased RP-201772 absorption and retention appeared to be the basis forZ. maysinjury when tank-mixed with metolachlor/benoxacor and applied to emergedZ. mays.