Influence of Soybean (Glycine max) Population and Herbicide Program on Palmer Amaranth (Amaranthus palmeri) Control, Soybean Yield, and Economic Return
Palmer amaranth (Amaranthus palmeri S. Wats) has become one of the most prominent and difficult weeds to control in soybean (Glycine max (L.) Merr.) in North Carolina. A survey was conducted in North Carolina during fall 2010 to estimate the magnitude of this problem. Palmer amaranth was present in 39% of 2,512 fields representing 0.24% of soybean ha in North Carolina. In recent years, growers have reduced soybean seeding rates in an effort to decrease production costs associated with technology fees. However, given the increase in prevalence of Palmer amaranth and the difficultly in controlling this weed due to herbicide resistance, growers may need to reconsider reductions in seeding rates. Therefore, research was conducted during 2010 and 2011 to determine if Palmer amaranth control, soybean yield, and economic return were affected by soybean plant population, preemergence (PRE) and postemergence (POST) herbicides, and herbicide resistant traits (glufosinate-resistant and glyphosate-resistant cultivars). Applying PRE or POST herbicides and increasing soybean population increased Palmer amaranth control, soybean yield, and economic return when compared with POST herbicides only or when lower soybean populations were present. Efficacy of glufosinate and glyphosate did not vary in most instances, most likely because these herbicides were applied timely, and the frequency of glyphosate resistance did not exceed 10% in these fields. 1. Introduction Effective weed management continues to be an important component of profitable soybean production in North Carolina. In recent years, herbicide-resistant weed populations have developed and have limited the effectiveness of herbicide options for growers. Populations of Palmer amaranth and horseweed (Conyza canadensis L.) in the coastal plain of North Carolina resistant to glyphosate have been confirmed [1, 2]. Resistance of Palmer amaranth to acetolactate synthase (ALS)-inhibiting herbicides also has been confirmed in North Carolina [1, 2]. Managing herbicide-resistant weed populations continues to be a challenge, especially Palmer amaranth, where alternatives to glyphosate and ALS-inhibiting herbicides require timely application [3, 4]. During fall 2010, 242 specific sites were sampled in North Carolina to determine the geographical range of Palmer amaranth and to determine if these populations were resistant to glyphosate. Of these specific sites, 52% had Palmer amaranth present with 98% of these populations expressing resistance to glyphosate and 85% expressing resistance to thifensulfuron-methyl [5].
References
[1]
I. Heap, “The international survey of herbicide resistant weeds,” 2012, http://www.weedscience.org.
[2]
J. R. Whitaker, Distribution, Biology, and Management of Glyphosate-Resistant Palmer Amaranth in North Carolina [PhD dissertation], North Carolina State University, Raleigh, NC, USA, 2009.
[3]
A. S. Culpepper, A. C. York, A. W. MacRae, and J. Kichler, “Glyphosate-resistant Palmer amaranth response to weed management programs in Roundup Ready and Liberty Link cotton,” in Proceedings of the Beltwide Cotton Conferences, National Cotton Council, Nashville, Tenn, USA, January 2008.
[4]
L. M. Sosnoskie, J. M. Kichler, R. D. Wallace, and A. S. Culpepper, “Multiple resistance in Palmer amaranth to glyphosate and pyrithiobac confirmed in Georgia,” Weed Science, vol. 59, no. 3, pp. 321–325, 2011.
[5]
A. E. Hoffner, D. L. Jordan, and A. C. York, “Geographical distribution of herbicide resistance in Palmer amaranth (Amaranthus palmeri) populations across North Carolina,” in Proceedings of the 7th International IPM Symposium: IPM on the World Stage, pp. 27–29, Memphis, Tenn, USA, March 2012.
[6]
A. S. Culpepper, T. L. Grey, W. K. Vencill et al., “Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) confirmed in Georgia,” Weed Science, vol. 54, no. 4, pp. 620–626, 2006.
[7]
T. M. Webster, “Weed survey—southern states: broadleaf crop subsection,” in Proceedings of the Southern Weed Science Society's meeting, vol. 62, pp. 517–520, 2005.
[8]
J. R. Whitaker, A. C. York, D. L. Jordan, and A. S. Culpepper, “Palmer amaranth (Amaranthus palmeri) control in soybean with glyphosate and conventional herbicide systems,” Weed Technology, vol. 24, no. 4, pp. 403–410, 2010.
[9]
D. B. Harder, C. L. Sprague, and K. A. Renner, “Effect of soybean row width and population on weeds, crop yield, and economic return,” Weed Technology, vol. 21, no. 3, pp. 744–752, 2007.
[10]
G. T. Place, S. C. Reberg-Horton, E. J. Dunphy, and A. N. Smith, “Seeding rate effects on weed control and yield for organic soybean production,” Weed Technology, vol. 23, no. 4, pp. 497–502, 2009.
[11]
T. C. Mueller, P. D. Mitchell, B. G. Young, and A. S. Culpepper, “Proactive versus reactive management of glyphosate-resistant or -tolerant weeds,” Weed Technology, vol. 19, no. 4, pp. 924–933, 2005.
[12]
M. D. K. Owen, “Weed species shifts in glyphosate-resistant crops,” Pest Management Science, vol. 64, no. 4, pp. 377–387, 2008.
[13]
D. R. Shaw, M. D. Owen, P. M. Dixon et al., “Benchmark study on glyphosate-resistant cropping systems in the United States. Part 1: introduction to 2006–2008,” Pest Management Science, vol. 67, no. 7, pp. 741–746, 2011.
[14]
D. A. Guillermo, P. Pedersen, and R. G. Hartzler, “Soybean seeding rate effects on weed management,” Weed Technology, vol. 23, no. 1, pp. 17–22, 2009.
[15]
O. W. Howe and L. R. Oliver, “Influence of soybean (Glycine max) row spacing on pitted morningglory (Ipomoea Lacunose) interference,” Weed Science, vol. 35, pp. 185–193, 1987.
[16]
G. R. W. Nice, N. W. Buehring, and D. R. Shaw, “Sicklepod (Senna obtusifolia) response to shading, soybean (Glycine max) row spacing, and population in three management systems,” Weed Technology, vol. 15, no. 1, pp. 155–162, 2001.
[17]
J. K. Norsworthy and J. R. Frederick, “Reduced seeding rate for glyphosate-resistant, drilled soybean on the southeastern coastal plain,” Agronomy Journal, vol. 94, no. 6, pp. 1282–1288, 2002.
[18]
J. K. Norsworthy and L. R. Oliver, “Effect of seeding rate of drilled glyphosate resistant soybean (Glycine max) on seed yield and gross profit margin,” Weed Technology, vol. 15, pp. 284–292, 2001.
[19]
R. J. Kratochvil, J. T. Pearce, and M. R. Harrison Jr., “Row spacing and seeding rate effects on glyphosate-resistant soybean for mid-Atlantic production systems,” Agronomy Journal, vol. 96, no. 4, pp. 1029–1038, 2004.
[20]
North Carolina Department of Agriculture and Consumer Services, “Crops summary: field crops, fruits, vegetables,” 2010, http://www.ncagr.gov/stats/crops/CropSummary.pdf.
[21]
G. Bullen, E. J. Dunphy, and E. Weddington, “Soybean budget-full season, conventional tillage,” 2010, North Carolina Cooperative Extension, http://www.ag-econ.ncsu.edu/extension/budgets/wheat/SoybeanFullConv2010.pdf.
[22]
W. J. Everman, “Chemical weed control in soybeans,” Pages 253–263 in 2012 North Carolina Agricultural Chemicals Manual, Pub. AG-1, 430 pages, 2012.
[23]
M. D. K. Owen and I. A. Zelaya, “Herbicide-resistant crops and weed resistance to herbicides,” Pest Management Science, vol. 61, no. 3, pp. 301–311, 2005.
