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Distribution of Conyza sp. in Orchards of California and Response to Glyphosate and Paraquat

  • Marcelo L. Moretti (a1), Lynn M. Sosnoskie (a1), Anil Shrestha (a2), Steven D. Wright (a3), Kurt J. Hembree (a4), Marie Jasieniuk (a1) and Bradley D. Hanson (a1)...


Resistance to glyphosate in hairy fleabane and horseweed is a problem in orchards and vineyards in California. Population genetic analyses suggest that glyphosate resistance evolved multiple times in both species, but it is unknown if resistance to other herbicides is also present. Two approaches of research were undertaken to further evaluate herbicide resistance in Conyza sp. in the perennial crop systems of California. In the initial study, the distribution of Conyza sp. in the Central Valley, using a semistructured field survey, was coupled with evaluation of the presence and level of glyphosate resistance in plants grown from field-collected seed. In a subsequent study, single-seed descendants representing distinct genetic groups were self-pollinated in the greenhouse and these accessions were evaluated for response to glyphosate and paraquat. Conyza sp. were commonly found throughout the Central Valley and glyphosate-resistant individuals were confirmed in all field collections of both species. The level of glyphosate resistance among field collections varied from 5- to 21-fold compared with 50% glyphosate resistance (GR50) of the susceptible, with exception of one region with a GR50 similar to the susceptible. When self-pollinated accessions from different genetic groups were screened, the level of glyphosate resistance, on the basis of GR50 values, ranged from 1.7- to 42.5-fold in hairy fleabane, and 5.9- to 40.3-fold in horseweed. Three accessions of hairy fleabane from different genetic groups were also resistant to paraquat (40.1- to 352.5-fold). One glyphosate-resistant horseweed accession was resistant to paraquat (322.8-fold), which is the first confirmed case in California. All paraquat-resistant accessions of Conyza sp. identified so far have also been resistant to glyphosate, probably because glyphosate resistance is already widespread in the state. Because glyphosate and paraquat resistances are found across a wide geographical range and in accessions from distinct genetic groups, multiple resistant Conyza sp. likely developed independently several times in California.


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[CDFA] California Department of Food and Agriculture (2015) California Agricultural Production Statistics. Accessed April 26, 2015
[CDPR] California Department of Pesticide Regulation (2013) Summary of Pesticide Use Report Data. Accessed April 20, 2015
Délye, C, Jasieniuk, M, Le Corre, V (2013) Deciphering the evolution of herbicide resistance in weeds. Trends Genet 29:649658
Eubank, TW, Nandula, VK, Poston, DH, Shaw, DR (2012) Multiple resistance of horseweed to glyphosate and paraquat and its control with paraquat and metribuzin combinations. Agronomy 2:358370
Ge, X, d'Avignon, DA, Ackerman, JJH, Duncan, B, Spaur, MB, Sammons, RD (2011) Glyphosate resistant horseweed made sensitive to glyphosate: low temperature suppression of glyphosate vacuolar sequestration revealed by 31P NMR. Pest Manag Sci 67:12151221
Gressel, J (2009) Evolving understanding of the evolution of herbicide resistance. Pest Manag Sci 65:11641173
Hanson, BD, Shrestha, A, Shaner, DL (2009) Distribution of glyphosate-resistant horseweed (Conyza canadensis) and relationship to cropping systems in the Central Valley of California. Weed Sci 57:4853
Kahle, D, Wickham, H, Kahle, MD, Suggests, M (2013) Package ‘ggmap’. Accessed April 6, 2015
McCullagh, P, Nelder, JA (1989) Generalized Linear Models. 2nd edn. London Chapman & Hall. p 511
Moretti, ML, Hanson, BD, Hembree, KJ, Shrestha, A (2013) Glyphosate resistance is more variable than paraquat resistance in a multiple-resistant hairy fleabane (Conyza bonariensis) population. Weed Sci 61:396402
Moretti, ML, Shrestha, A, Hembree, KJ, Hanson, BD (2015) Postemergence control of glyphosate/paraquat-resistant hairy fleabane (Conyza bonariensis) in tree nut orchards in the Central Valley of California. Weed Technol 29:501508
Okada, M, Hanson, BD, Hembree, KJ, Peng, Y, Shrestha, A, Stewart, CN, Wright, SD, Jasieniuk, M (2013) Evolution and spread of glyphosate resistance in Conyza canadensis in California. Evol Appl 6:761777
Okada, M, Hanson, BD, Hembree, KJ, Peng, Y, Shrestha, A, Stewart, CN, Wright, SD, Jasieniuk, M (2014) Evolution and spread of glyphosate resistance in Conyza bonariensis in California and a comparison with closely related Conyza canadensis . Weed Res 55:173184
Okada, M, Jasieniuk, M (2014) Inheritance of glyphosate resistance in hairy fleabane (Conyza bonariensis) from California. Weed Sci 62:258266
R Development Core Team (2015) The R Project for Statistical Computing. Accessed June 29, 2015
Ritz, C, Strebig, J, Ritz, MC (2015) Package ‘drc’. Accessed May 16, 2015
Sammons, RD, Gaines, TA (2014) Glyphosate resistance: state of knowledge. Pest Manag Sci 70:13671377
Shrestha, A, Hanson, BD, Hembree, KJ (2008a) Glyphosate-resistant hairy fleabane documented in the Central Valley. Calif Agric 62:116119
Shrestha, A, Hembree, KJ, Va, N (2007) Growth stage influences level of resistance in glyphosate-resistant horseweed. Calif Agric 61:6770
Shrestha, A, Hembree, KJ, Wright, SD (2008b) Biology and management of horseweed and hairy fleabane in California. University of California Division of Agricultural and Natural Resources Pub 8314. 9 p
Shrestha, A, Steinhauer, KM, Moretti, ML, Hanson, BD, Jasieniuk, M, Hembree, KJ, Wright, SD (2014) Distribution of glyphosate-resistant and glyphosate-susceptible hairy fleabane (Conyza bonariensis) in central California and their phenological development. J Pest Sci 87:201209
VanGessel, M (2001) Glyphosate-resistant horseweed from Delaware. Weed Sci 49:703705
Walker, S, Bell, K, Robinson, G, Widderick, M (2011) Flaxleaf fleabane (Conyza bonariensis) populations have developed glyphosate resistance in north-east Australian cropping fields. Crop Prot 30:311317
Yuan, JS, Abercrombie, LLG, Cao, Y, Halfhill, MD, Zhou, X, Peng, Y, Hu, J, Rao, MR, Heck, GR, Larosa, TJ, Sammons, RD, Wang, X, Ranjan, P, Johnson, DH, Wadl, PA, Scheffler, BE, Rinehart, TA, Trigiano, RN, Stewart, CN Jr. (2010) Functional genomics analysis of horseweed (Conyza canadensis) with special reference to the evolution of non–target-site glyphosate resistance. Weed Sci 58:109117



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