Glyphosate weed resistance

Padgette, S.R., X. Delannay, L.D. Bradshaw, B.H. Wells, and G. Kishore (1995). Development of glyphosate-tolerant crops and perspectives on the potential for weed resistance to glyphosate, p. 154. In De Prado, R., Garcia-Torres, L., and Jorrin, J., eds., International Symposium on Weed and Crop Resistance to Herbicides. Cardoba, Spain Cardobesa de Impresiones Graficas, SL. Abstract, 92. 

Development of weed resistance to triazine herbicides has necessitated alternative weed control strategies. Rotation of triazines with other herbicides and combining triazines with other chemistries has been effective in ornamentals and Christmas tree plantations (Van Himme, 1989). Supplemental treatments in Christmas trees have been effective, using directed sprays of phenoxy herbicides or glyphosate before resistant weeds mature and produce seeds. Weed resistance from triazines is not a problem in most forest settings where the herbicide is applied only once or twice in a rotation, since 1 or 2 years of herbaceous weed control normally ensures survival and eventual dominance by conifers. When the conifer canopy closes, virtually all herbaceous vegetation is shaded out for some decades hence resistant weeds, if present, fail to survive from one generation to the next. 

Finally, weed shifts observed in genetically modified crops, caused by the development of weed resistance to the widely used glyphosate herbicide, will offer market opportunities for herbicides with other modes of action, such as Protox-inhibiting herbicides. 

Other developments include the introduction of hybrid lines resistant to glyphosate and glufosinate. Glyphosate-resistance technology was rapidly adopted for soybean, but was more slowly adopted for field corn due to corn s slower canopy closure. Acceptance of glufosinate-resistant weed control technology faced the same obstacles, but has been even less competitive economically due to product cost. 

With the culture of soybean and field com so intimately intertwined throughout the Midwest, changes in soybean weed control affect com weed control as well. One real effect of the widespread adoption of glyphosate-tolerant varieties has been the disincentive to discover and develop new products and new chemistries. Since the advent of glyphosate-resistant soybean, very few products have been developed for that market. 

Several weed species resistant to glyphosate have recently developed in several geographical areas of the United States. This further supports the need for keeping a broad range of herbicides, such as the triazines, available for weed management programs. 

Glyphosate resistance in weeds has already been reported in many areas (at least 15 US states, three Australian states, and seven other countries) and in at least 12 weed species (Pratley et al., 1996 Lorraine-Colwill et al, 1999 Lee and Ngim, 2000 Van Gessel, 2001 Perez and Kogan, 2002 Heap 2006) as summarized in Table 11.5. 

Throughout western Canada and the central Great Plains of North America, volunteer wheat is becoming a more serious problem (Leeson el al., 2005). This may become a special concern if the volunteer wheat is glyphosate-resistant (Harker el al., 2005). There are also many examples of integration of traits from weeds into crops, and there is some evidence of spread from herbicide-resistant crops into weeds (Gressel, 2002). 

Boutsalis, P. (2001). Herbicide Resistance Action Committee (HRAC) Web page http //plantprotection.org/HRAC Bradshaw, L.D., S.R. Padgette, S.L. Kimball, and B.H. Wells (1997). Perspectives on glyphosate resistance. Weed Technol., 11 189-198. Bravin, F., A. Onofri, G. Zanin, and M. Sattin (2004). Is malathion a useful tool to infer the chlorsulfuron-resistance mechanism in mul-tiresistant Italian populations of Lolium spp. 4th International Weed Science Congress, p. 52, S15MT08P00. 

Cairns, A.L.P. and F.H. Eksteen (2004). Glyphosate and paraquat resistance in weeds of the Western Cape. 4th International Weed Science Congress, p. 20, S17MT08P03. 

Feng, P.C.C., M. Tran, T. Chiu, R.D. Sammons, G.R. Heck, and C.A. CaJacob (2004). Investigations into glyphosate-resistant horseweed (Conyzja canadensis) Retention, uptake, translocation, and metabolism. Weed Sci., 52 498-505. 

Neve, P, J. Sadler, and S.B. Powles (2004). Multiple herbicide resistance in a glyphosate-resistant rigid ryegrass (Lolium rigidum) population. Weed Sci. 52 920-928. 

Perez, A. and M. Kogan (2002). Glyphosate-resistant Italian ryegrass (Lolium multiflorum Lam.) in Chile. International Weed Science Societhy, Newsletter, January. Madison, WI IWSS. 

Powles, S.B., D.F. Lorraine-Colwill, J.J. Dellow, and C. Preston (1998). Evolved resistance to glyphosate in rigid ryegrass (Lolium rigidum) in Australia. Weed Sci., 46 604—607. 

Van Gessel, M.J. (2001). Glyphosate-resistant horseweed from Delaware. Weed Sci., 50 703-705. 

Vila-Aiub, M.M., C. Balbi, P.C. Gundel, C.M. Ghersa, and S.B. Powles (2007). Rapid evolution of glyphosate-resistant sorghum halepense (johnsongrass) in glyphosate resistant soybeans. Weed Sci., 55(6) 566-571. 

Wakelin, A.M. and C. Preston (2004). Evolution of glyphosate resistance in New South Wales, Australia. 2004. 4th International Weed Science Congress, p. 61, S17MT08P04. 

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