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ARS Home » Southeast Area » Auburn, Alabama » Soil Dynamics Research » Research » Publications at this Location » Publication #236413
Title: Glyphosate resistant palmer amaranth - a threat to conservation tillage

Author
item Price, Andrew
item REEVES, DONALD
item LAMM, DAVID - USDA-NRCS

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/2/2009
Publication Date: 2/2/2009
Citation: Price, A.J., Reeves, D.W., Lamm, D.A. 2009. Glyphosate resistant palmer amaranth - a threat to conservation tillage. In: Boyd, S., et al., editors. Proceedings of the National Cotton Council Beltwide Cotton Conference, January 5-8, 2009, San Antonio, Texas. p. 1335-1336.

Interpretive Summary: Glyphosate resistant Palmer amaranth is now present in Alabama, Arkansas, Georgia, Mississippi, North Carolina, South Carolina, and Tennessee. Hundreds of thousands of conservation tillage cotton acres, some currently under USDA Natural Resources Conservation Service (NRCS) conservation program contracts, are at risk of being converted to higher-intensity tillage systems. The shift to higher intensity tillage facilitates seed burial as well as preplant incorporated and preemergence herbicide control of this problematic weed, especially in dryland cotton production. Due to the threat of glyphosate resistant pigweed to conservation agriculture, a USDAARS/Cotton Inc. sponsored workshop involving southeastern stakeholders was held in Athens, GA on Aug. 11th, 2008. The following is an abbreviated list of the solutions offered: • Crop rotation intensification (including pasture-based rotations ) • Improve residual herbicide performance in dry-land conservation systems • Weed management intensification (scouting, timely applications, ect.) • Integration of cultural solutions (high residue cover crops, delayed cotton planting, etc.) • High residue cultivators • Deep tillage to bury seed bank followed by a continuous high residue conservation system • Alternative herbicide chemistries • New cotton herbicide paradigm for Coastal Plain /Uplands/ Delta regions: site-specific • Use of fall residuals on harvested fallow fields to reduce weed seedbank Depending on the severity of glyphosate Palmer amaranth infestation, multiple strategies involving integration of cultural as well as chemical weed control will be needed to overcome this threat. Integrating high-residue cover crop systems may help facilitate Palmer control in row middles; however, Palmer emerging in the crop row remains a threat to cotton performance, especially in dryland cotton. Much research is needed to solve this threat to conservation tillage cotton production.

Technical Abstract: Since the mid 1980’s, conservation tillage has been recognized as a beneficial alternative to conventional tillage practices. With definite advantages over traditional tillage practices, conservation tillage adoption remained sluggish through the 80’s and mid 90’s due, in large part, to poor weed control and weed control options available for these systems. A turning point for conservation tillage was reached when, in 1996, Monsanto introduced Roundup Ready® soybean and subsequent glyphosate-resistant crops offered a successful alternative to conventional weed management that could be incorporated into conservation agriculture systems. Glyphosate resistant Palmer amaranth is now present in Alabama, Arkansas, Georgia, Mississippi, North Carolina, South Carolina, and Tennessee. Hundreds of thousands of conservation tillage cotton acres, some currently under USDA Natural Resources Conservation Service (NRCS) conservation program contracts, are at risk of being converted to higher-intensity tillage systems. The shift to higher intensity tillage facilitates seed burial as well as preplant incorporated and preemergence herbicide control of this problematic weed, especially in dry-land cotton production. NRCS defines conservation agriculture as cropping systems that maintain a minimum 30% residue on the soil surface. Recent NRCS programs such as EQIP, the Conservation Security Program and the recently enacted 2008 Farm Bill Conservation Stewardship Program offer incentive contracts rewarding conservation. Cropping systems with higher resource conservation receive higher payments; in many states, use of high residue cover crops increase payments. Due to the threat of glyphosate resistant pigweed to conservation agriculture, a USDA-ARS/Cotton Inc. sponsored workshop involving southeastern stakeholders was held in Athens, GA on Aug. 11th, 2008. The following is an abbreviated list of the solutions offered: • Crop rotation intensification (including pasture-based rotations ) • Improve residual herbicide performance in dry-land conservation systems • Weed management intensification (scouting, timely applications, ect.) • Integration of cultural solutions (high residue cover crops, delayed cotton planting, etc.) • High residue cultivators • Deep tillage to bury seed bank followed by a continuous high residue conservation system • Alternative herbicide chemistries • New cotton herbicide paradigm for Coastal Plain /Uplands/ Delta regions: site-specific • Use of fall residuals on harvested fallow fields to reduce weed seedbank Depending on the severity of glyphosate Palmer amaranth infestation, multiple strategies involving integration of cultural as well as chemical weed control will be needed to overcome this threat. Integrating high-residue cover crop systems may help facilitate Palmer control in row middles; however, Palmer emerging in the crop row remains a threat to cotton performance, especially in dryland cotton. Much research is needed to solve this threat to conservation tillage cotton production.