Submitted to: Weed Science
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2003
Publication Date: February 7, 2004
Citation: Molin, W.T. 2004. Contributions of preemergence herbicides and tillage to weed control in glyphosate tolerant cotton [abstract]. Weed Science Society of America. p. 44. Technical Abstract: A two-year field experiment was established in 2002 to investigate the effects of tillage and glyphosate, alone or in combination with preemergence herbicides, on weed populations in glyphosate tolerant wide (40-inches) row and ultra narrow (10-inches) row cotton. Glyphosate is an important component in reduced tillage systems and may allow the exclusion of other herbicides in Roundup Ready crops. However, reduction in herbicide usage or tillage in cotton, particularly in regions with high rainfall and warm temperatures, may not be viable options due to rapid re-establishment of weeds. Specific objectives were to determine changes in weed populations at the beginning and end of the season with respect to tillage, herbicide treatments and row spacing. Soil management consisted of no tillage, herbicide treatments and row spacing. Soil management consisted of no tillage, or fall seed bed preparation consisting of bed formation (hipping), deep tillage of beds, and re-formation of beds in the fall. Preemergence herbicide treatments were fluometuron and metolachlor applied at 1.12 kg ha**-1. In treatments receiving preemergence herbicides, glyphosate was applied preplant at 1.12 kg ha**-1, and at the first and four leaf stages of cotton growth. Treatments in which preemergence herbicides were not used received an additional post-directed application of glyphosate at the eight-leaf stage in wide row cotton, or a post application of clethodim (0.28 kg ha**-1) and pyrithiobac (77 g ha**-1) in ultra narrow row cotton. Before canopy closure, populations were reduced to near zero with glyphosate treatments but were re-established between glyphosate treatments. Inclusion of preemergence herbicides resulted in a four to six fold reduction in weed populations over glyphosate alone treatments. Similar reductions were obtained in tillage over no tillage treatments. Weed populations were two to eight fold greater in wide row than in ultra narrow row cotton with no preemergence herbicides but were equivalent between row spacings with preemergence herbicides. Brown top millet (Brachiaria ramose (l.) Stapf), goosegrass (Eleucine indica (L.) Gaertn.) and spurge (Euphorbia hyssopifolia L.) were the most prevalent weeds at pre-canopy closure, but after defoliation, brown top millet and spurge were most abundant. Yields were not reduced by treatments. Including preemergence herbicides in a glyphosate-based cotton management program resulted in an acceptable level of weed control throughout the season.