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Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/12/2003 Publication Date: 1/1/2004 Citation: Reddy, K.N. 2004. Weed control and species shift in bromoxynil- and glyphosate-resistant cotton (gossypium hirsutum) rotation systems. Weed Technology. 18:131-139. Interpretive Summary: Transgenic crops such as bromoxynil-resistant (BR) and glyphosate-resistant (GR) cotton have provided farmers some flexibility to manage weeds. However, information on the impact of continuous BR and GR cotton production on weed control and species shift and the benefits of rotation of these systems is lacking. A scientist at the Southern Weed Science Research Unit in Stoneville, Mississippi completed a three-year study assessing various rotation, row spacing, and herbicide programs. Control of certain annual broadleaf weeds was greater than 97% regardless of row width, rotation, and herbicide program. However, for common purslane, sicklepod, and smooth pigweed control was better with glyphosate in GR cotton than bromoxynil in BR cotton. Three years of continuous BR cotton resulted in higher densities of certain weeds compared to continuous GR cotton. Seed cotton yield was lower in continuous BR cotton compared to the other rotation systems and yields greatly improved when BR cotton was rotated with GR cotton. These results demonstrated that the shift in spectrum of weeds towards more tolerant species and yield drag in continuous BR cotton might be prevented by rotating BR with GR cotton. Technical Abstract: A field study was conducted during 1999 through 2001 at Stoneville, MS, to determine the effects of bromoxynil-resistant (BR) and glyphosate-resistant (GR) cotton rotation systems under narrow (25 cm spacing) and wide (102 cm spacing) row planting on weed control, weed density and shift, and cotton yield. The four rotations over 3 years included BR-BR-BR, GR-GR-GR, BR-GR-BR, and GR-BR-GR; all with bromoxynil or glyphosate postemergence (POST) only or following fluometuron plus pendimethalin preemergence (PRE). Control of hemp sesbania, pitted morningglory, prickly sida, and hyssop spurge was 97% regardless of row width, rotation, and herbicide program. Control of common purslane, sicklepod, and smooth pigweed was higher with glyphosate POST in GR cotton than bromoxynil POST in BR cotton. Broadleaf and yellow nutsedge weed biomass were higher with bromoxynil POST in BR cotton than glyphosate POST in GR cotton. Continuous BR cotton system resulted in higher densities of common purslane, sicklepod, and yellow nutsedge (15.3, 1.5, and 373 plants/m2, respectively) compared to continuous GR cotton (0.7, 0.1, and 1.0 plant/m2, respectively). Seed cotton yield was consistently higher in wide compared to narrow row cotton. Seed cotton yield was lower in continuous BR cotton compared to the other three rotation systems and yields greatly improved when BR cotton was rotated with GR cotton. Over a 3-yr period, seed cotton yields with glyphosate POST only (4,000 to 4,890 kg/ha) or following PRE herbicides (4,480 to 4,860 kg/ha) were similar in GR cotton, whereas, in BR cotton, bromoxynil POST only (1,390 to 4,280 kg/ha) resulted in lower yield compared to bromoxynil POST following PRE herbicides (2,550 to 4,480 kg/ha). The results indicated that the shift in spectrum of weeds towards more tolerant species and yield drag in continuous BR cotton can be prevented by rotating BR with GR cotton. |
