Glyphosate-resistant Palmer amaranth: A threat to conservation tillage

Abstract

Conservation tillage reduces the physical movement of soil to the minimum required for crop establishment and production. When consistently practiced as a soil and crop management system, it greatly reduces soil erosion and is recognized for the potential to improve soil quality and water conservation and plant available water. Adoption of conservation tillage increased dramatically with the advent of transgenic, glyphosate-resistant crops that permitted in-season, over-the-top use of glyphosate (N-[phosphonomethyl] glycine), a broad-spectrum herbicide with very low mammalian toxicity and minimal potential for off-site movement in soil or water. Glyphosate-resistant crops are currently grown on approximately 70 million ha (173 million ac) worldwide. The United States has the most hectares (45 million ha [99 million ac]) of transgenic, glyphosate-resistant cultivars and the greatest number of hectares (46 million ha [114 million ac]) in conservation tillage. The practice of conservation tillage is now threatened by the emergence and rapid spread of glyphosate-resistant Palmer amaranth (Amaranthus palmeri [S.] Wats.), one of several amaranths commonly called pigweeds. First identified in Georgia, it now has been reported in Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Tennessee. Another closely related dioecious amaranth, or pigweed, common waterhemp (Amaranthus rudis Sauer), has also developed resistance to glyphosate in Illinois, Iowa, Minnesota, and Missouri. Hundreds of thousands of conservation tillage hectares, some currently under USDA Natural Resources Conservation Service conservation program contracts, are at risk of being converted to higher-intensity tillage systems due to the inability to control these glyphosate-resistant Amaranthus species in conservation tillage systems using traditional technologies. The decline of conservation tillage is inevitable without the development and rapid adoption of integrated, effective weed control strategies. Traditional and alternative weed control strategies, such as the utilization of crop and herbicide rotation and integration of high residue cereal cover crops, are necessary in order to sustain conservation tillage practices. Key words: conservation tillage-herbicide resistance-resistant pigweedThe benefits of conservation tillage are under threat. Crop production has historically relied on tillage to prepare a smooth, weed-free seedbed and to incorporate fertilizer and lime (Gebhardt et al. 1985). Conservation tillage systems were originally developed to reduce soil erosion but have more recently been recognized for improving soil quality and water availability (Reeves 1994(Reeves , 1997Kaspar et al. 2001). Large-scale successful implementation of conservation tillage across the United States came only after the introduction of broad-spectrum herbicides for weed control and the development of planters capable of penetrating crop residues to place seed directly into the soil (Triplett and Dick 2008)...

Impact of tembotrione and flufenacet plus isoxaflutole application timings, rates, and adjuvant type on weeds and yield of maize

“…Intensive use of herbicides is associated with soil and water pollution and additionally with selection of herbicide resistant weed biotypes (Price et al, 2011). To reduce the cost of intensive herbicide application, environment pollution and enhance biological effectiveness, methods of weed control should be optimized.…”

Evaluation of POST-Harvest Herbicide Applications for Seed Prevention of Glyphosate-Resistant Palmer amaranth (Amaranthus palmeri)

“…As tillage has been reduced, reliance on herbicides for weed management has increased, presenting a new set of challenges for producers. Weed populations tend to increase in conservation tillage; thus, for species like Palmer amaranth, enforcing a zerotolerance seed production policy is vital (Price et al 2011). The importance of controlling late-season weed escapes and subsequent seed production is critical in effectively managing the long-term soil seedbank.…”

Integrated Palmer Amaranth Management in Glufosinate-Resistant Cotton: I. Soil-Inversion, High-Residue Cover Crops and Herbicide Regimes

“…However, the return to conventional tillage to control glyphosate-resistant Palmer amaranth threatens to reduce conservation tillage practices. Some researchers [35,36] advocate the integration of traditional and alternative weed control strategies, such as the utilization of crop and herbicide rotation and integration of high residue cereal cover crops in order to sustain conservation tillage practices.…”