Preplant Weed Control in Conservation Tillage Cotton-Approaches and Options

Stephen H. Crawford and Kenny D. Leake


 
ABSTRACT

Four approaches to preplant weed control on fall bedded Sharkey clay soil have been evaluated in field experiments at the Northeast Research Station near St. Joseph, Louisiana, from 1989-1991. These included fall application of residual herbicides before cool season weeds emerged; and mid-winter, late winter, or spring applications of burndown or burndown plus residual herbicides. Shallow tillage with a disk bedder was used as a comparison in some experiments.

Fall residual treatments were surface applications of Coal and Bladex 4L, and soil incorporated Treflan and Zorial. Goal controlled the broadest spectrum of weeds; however, other herbicides controlled many species. None of the treatments provided a weed-free seedbed at planting in late April. Tolerant species increased each year when treatments were repeated on the same, plots, and in some experiments, bare soil from fall treatments encouraged smartweed emergence.

Postemergence treatments included mid-winter applications of 2,4-D low volatile ester followed by Roundup 2-3 weeks preplant, mid-winter applications of Roundup + Goal and Gramoxone Extra + Goal, and spring preplant treatments of Roundup and Gramoxone Extra alone and in Goal tank-mixes. These treatments were compared to two rebedding. Annual bluegrass, sibara, shepherdspurse, Carolina foxtail, and common chickweed were adequately controlled in all treatments. Henbit was not always controlled by Roundup alone; however, tankmixtures of Goal + Roundup most often provided effective control - Cutleaf evening primrose was most effectively controlled by 2,4-D low volatile ester. However, Roundup alone and Gramoxone tank-mixtures were moderately effective.

Smartweed control was evaluated in treatments applied in late winter to 4-6 leaf seedlings. Initial control was excellent with both Roundup and Gramoxone alone, and tank-mixtures of these herbicides with Goal. However, control at planting was complete only in tank mixture treatments, apparently due to both enhanced postemergence and soil residual control.



Reprinted from 1992 Proceedings Beltwide Cotton Conferences pg. 1319
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998