Abstract: Several herbicide-based weed management programs for glyphosate-tolerant cotton were compared in eight field studies across Alabama during 1996 and 1997. Weed management programs ranged from traditional, soil-applied residual herbicide programs to more recently developed total postemergence (POST) herbicide programs. Pitted morningglory and sicklepod control was best achieved with fluometuron applied preemergence (PRE) followed by (fb) a single POST over-the-top (POT) application of glyphosate fb a POST-directed application of glyphosate. Annual grass control was better with the preplant incorporated (PPI) programs at two of three locations in both years. Treatments that included at least one glyphosate POT application gave increased grass control over no glyphosate or pyrithiobac POT. Velvetleaf control was improved with the addition of glyphosate POT. A herbicide program using no POST herbicides yielded significantly less seed cotton than any program using POST herbicides at one location. PRE- and POST-only weed management programs at another location produced more seed cotton and gave greater net returns than PPI programs. Similarly, net returns at that same location were equivalent for both PRE- and POST-only programs, and less for PPI programs. POST-only programs yielded highest amounts of seed cotton and netted greater returns.
Nomenclature: Fluometuron; glyphosate; pyrithiobac; cotton, Gossypium hirsutum L. ‘Deltapine 5415RR’, ‘Deltapine 5690RR’; pitted morningglory, Ipomoea lacunosa L. #3 IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; velvetleaf, Abutilon theophrasti Medik. # ABUTH.
Additional index words: Cotton yields, herbicide costs, herbicide-resistant crops, transgenic cotton.
Abbreviations: ANOVA, analysis of variance; EPDS, early postemergence-directed spray; EPOT, early postemergence over-the-top; fb, followed by; GCS, Gulf Coast Research and Education Center; LPDS, late postemergence-directed spray; LPOT, late postemergence over-the-top; LSD, least significant difference; PDS, postemergence-directed spray; PEF, Prattville Experimental Field; POST, postemergence; POT, postemergence over-the-top; PPI, preplant incorporated; PRE, preemergence; TVS, Tennessee Valley Research and Education Center; WGS, Wiregrass Research and Education Center.