Weed control and Zea mays tolerance as affected by timing of RP-201772 application

Field studies were conducted in 1996 and 1997 to determine the effects of R P-201772 and RP-201772 tank mixtures applied to emerged Zea mays. RP-201772 at 105 g ha(-1) and rank-mixed metolachlor/benoxacor or atrazine were appl ied pre-emergence and to spike, 2-leaf, and 4-leaf Z. mays. Herbicide treat ments over the four application timings provided greater than 90% Chenopodi um album, Ambrosia artemisiifolia, Amaranthus retroflexus, and Abutilon the ophrasti control. However, Setaria faberi control Varied among years and ap plication 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-l eaf Z. mayr, respectively. Greenhouse studies confirmed Z. mays sensitivity from delayed applications of RP-201772 tank-mixed with metolachlor/benoxac or. Similarly, increased Z. mays injury was observed from postemergence app lications of RP-201772 tank-mixed with acetochlor/MON-13900. Herbicide abso rption, translocation, metabolism, and retention studies were conducted to determine the physiological basis for the observed Z. mays injury from dela yed applications of the RP-201772 rank mixture with metolachlor/benoxacor. Metolachlor/benoxacor increased radiolabeled RP-201772 absorption when appl ied to spike, 2-leaf, and 4-leaf Z. mays. RP-201772 translocation and metab olism did not explain enhanced Z. mays injury. However, RP-201772 retention increased five-fold when metolachlor/benoxacor was present in the spray so lution and applied to 2-leaf and 4-leaf Z. mays. Increased RP-201772 absorp tion and retention appeared to be the basis for Z. mays injury when tank-mi xed wi th metolachlor/benoxacor and applied to emerged Z mays.