| Dinitroaniline-resistant Palmer amaranth control in cotton with metolachlor, commercially-available cotton herbicides, and pyrithiobac was evaluated in field studies in Calhoun County, SC. Preemergence(PRE), early postemergence over-the-top (EPOST), mid postemergence over-the-top (MPOST), and at cracking (AC) treatments were broadcast. Early postemergence-directed (EPD), mid postemergence-directed (MPD), late postemergence-directed (LPD), and lay-by (LB) treatments were applied on a 51 cm band over the row. Dry conditions in 1993 resulted in unacceptable Palmer amaranth control in all studies.;Metolachlor alone provided poor (3 to 44%) Palmer amaranth control 3 weeks after planting (WAP). Combinations of trifluralin plus metolachlor did not improve control compared to trifluralin alone. In 1992, Palmer amaranth control with commercially-available herbicides was generally unacceptable due to inadequate preemergence control and/or dry conditions; whereas, in 1994 control was marginal to unacceptable despite favorable growing conditions.;Pyrithiobac applied PRE at 0.053 kg ai ha;Palmer amaranth biomass levels and seed cotton yields generally reflected control ratings 7 WAP for all treatments. Only treatments with pyrithiobac attained seed cotton yields similar to weed-free cotton.;In the 1993 SC cotton growers survey, 78% of the respondents reported their problems with Palmer amaranth had increased since 1989 and 81% included Palmer amaranth among their five most troublesome weeds. Handweeding, rope wicking, extra cultivations, and extra herbicide treatments to control Palmer amaranth were used on 27, 30, 27, and 29%, respectively, of their cotton land at a cost exceeding ;From 1992 to 1995, an 85% reduction in Palmer amaranth seeds was observed in samples from a field in agronomic production without additional Palmer amaranth seed production. However, nearly 20 million seeds per ha remained in the top 15.24 cm soil in 1995. |
