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United States Department of Agriculture

Agricultural Research Service

2007 Annual Report

1a.Objectives (from AD-416)
Assess biological and ecological characteristics of weeds that contribute to their invasive and adaptive potential in an effort to provide more effective weed control tactics. Determine specific morphological and physiological characteristics of herbicide-resistant weed biotypes (e.g., horseweed), and invasive (e.g., cogongrass), native and non-native (e.g., pitted morningglory, purple nutsedge, johnsongrass) weed species and causes for their variable control with herbicides. Develop and/or refine effective, economical, environmentally safe, and sustainable weed management systems for cotton, soybean, and corn by integrating chemical, cultural, and herbicide-resistant cultivars with a greater emphasis on conservation tillage practices. Determine ecological changes that occur in the weed populations as a consequence of cultural practices and herbicide changes, including weed species shifts, changes in seed bank dynamics, and the development of herbicide resistance. Investigate mechanism of resistance in glyphosate-resistant horseweed. Assess risks associated with glyphosate-resistant cropping systems on soil microbial ecology, soybean diseases, and nitrogen fixation/assimilation.

1b.Approach (from AD-416)
Sustainable integrated weed management systems will be developed by integrating chemical, cultural, and mechanical control methods to exploit the benefits of each practice to minimize herbicide inputs and to maximize weed control and yield. Focus will be on use of conservation tillage, cover crops, crop rotation, narrow row spacing, competitive cultivars, and herbicide-resistant crops to reduce herbicide use and risks. Research will evaluate changes in the distribution and type of weed species and seed bank dynamics as a consequence of changes in production practices, such as herbicide-resistant crops, cover crops, row spacing, and conservation tillage. A broad range of techniques will used to assess biology and management of weed species and impact of herbicide-resistant cropping systems on weed populations and species shifts and resistance. Investigations will include biological and ecological aspects of a number of pernicious, noxious, and invasive weeds to understand the traits that lead to weediness and devise effective control measures.

3.Progress Report

Glyphosate metabolism in glyphosate resistant and susceptible soybean and canola. -- Genetically modified crops resistant to the glyphosate (Roundup Ready®) are widely used in North America. Glyphosate may occasionally injure glyphosate-resistant (GR) soybean due to accumulation of AMPA, a metabolite of glyphosate formed by plants. Scientists from Delta Research and Extension Center, Mississippi State University, and USDA ARS, Southern Weed Science Research Unit, Stoneville, MS; and USDA ARS, Natural Products Utilization Research Unit, Oxford, MS, have studied response and fate of glyphosate in GR and glyphosate sensitive (non GR) soybean and canola. The results show that GR soybean and canola were about 50 fold more tolerant to glyphosate than non GR varieties. Glyphosate caused injury in GR soybean, but did not injure GR canola, despite the fact that canola is quite sensitive to AMPA. These results demonstrated that AMPA formed from glyphosate could have been metabolized to non-phytotoxic metabolites before causing injury to GR canola.

Identification of glyphosate tolerant Italian ryegrass populations from Mississippi. -- The intense use of glyphosate and continued adoption of glyphosate-resistant crops without rotation with non-glyphosate-resistant crops has increased the selection pressure to evolve resistance in certain weed populations. Scientists from Delta Research and Extension Center, Mississippi State University and USDA-ARS, Southern Weed Science Research Unit, Stoneville, MS, have characterized two Italian ryegrass populations from Mississippi, suspected to be tolerant to glyphosate. These two populations were 3-fold more tolerant to glyphosate compared to the susceptible population. This is the first report of glyphosate-resistant Italian ryegrass populations from glyphosate-resistant cotton and glyphosate-resistant soybean cropping systems.

Cogongrass. -- Cogongrass continues to spread northward in the U.S. Recent field surveys have determined its presence in more than 75% of the counties in Mississippi, including the first sites in agricultural and non-agricultural areas in the Yazoo-Mississippi Delta Region. A highly effective non-herbicide method of killing cogongrass using heat was developed by scientists at the Southern Weed Science Research Unit (SWSRU). Industry and public utilities and departments of transportation have yet to implement this new methodology.

Deeprooted sedge. -- Deeprooted sedge is an invasive weed that is spreading at an alarming rate in the southeastern US. Scientists at the Southern Weed Science Unit conducted cooperative studies to determine its spread and invasion in agricultural and natural areas. These published studies indicated that deeprooted sedge has the capability to continue to spread and infest areas in addition to the currently known sites in 64 counties in six southeastern states.

Rye cover crop-based cotton production. -- The use of a rye cover crop in cotton promoted the growth and establishment of brown top millet, a serious weed in cotton. It is not clear whether the rye acted as a barrier to herbicide treatment resulting in less herbicide damage to the millet or provided an environment more favorable to its growth. Browntop millet can pose a serious threat to cotton because its long stems and leaves intertwine with cotton fiber during harvest resulting in excessive cotton fiber contamination during ginning. These results show that each component of a crop management scenario must be evaluated completely in order to establish its contribution, whether negative or positive, to crop production. In this case, cover crops can provide negative results on weed populations and have detrimental consequences in crops such as cotton.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of non-peer reviewed presentations and proceedings25
Number of newspaper articles and other presentations for non-science audiences8

Review Publications
Bryson, C.T., Koger III, C.H., Byrd, J.D. 2007. Effects of temperature and exposure period to heat on cogongrass (imperata cylindrical) viability. Weed Technology 21:141-144.

Reddy, K.N., Locke, M.A., Koger III, C.H., Zablotowicz, R.M., Krutz, L.J. 2006. Cotton and corn rotation under reduced tillage management: impacts on soil properties, weed control, yield, and net return. Weed Science 54:768-774.

Nandula, V.J., Poston, D.H., Reddy, K.N., Koger Iii, C.H. 2007. Formulation and adjuvant effects on uptake and translocation of 14**c clethodim in bermudagrass (cynodon dactylon). Weed Science 55:6-11.

Nandula, K.K., Poston, D.H., Eubank, T.W., Koger III, C.H., Reddy, K.N. 2007. Differential Response to Glyphosate in Italian Ryegrass (Lolium multiflorum) Populations from Mississippi. Weed Technology 21:477-482.

Bettmann, G.T., Ratnayaka, H.H., Molin, W.T., Sterling, T.M. 2006. Physiological and antioxidant responses of cotton and spurred anoda (anoda cristata)under nitrogen deficiency. Weed Science 54:641-650.

Molin, W.T., Boykin, D.L., Hugie, J.A., Ratnayaka, H.H., Sterling, T.M. 2006. Spurred Anoda (Anoda cristata) Interference in Wide Row and Ultra Narrow Row Cotton. Weed Science. 54:651-657.

Rosen, D.J., R. Carter, and C.T. Bryson. 2006. The recent spread of Cyperus entrerianus (Cyperaceae) in the southeastern United States and its invasive potential in bottonland hardwood forests. Southeastern Naturalist 5:333-344.

Sanyal, D., Bhowmik, P.C., Reddy, K.N. 2006. Influence of leaf surface micromorphology, wax content, and surfactant on primisulfuron droplet spread on barnyardgrass and green foxtail. Weed Science 54:627-633.

Nandula, V.K., Eubank, T.W., Poston, D.H., Koger Iii, C.H., Reddy, K.N. 2006. Factors effecting germination of horseweed (conyza canadensis). Weed Science. 54: 898-902.

Burke, I.C., Koger Iii, C.H., Reddy, K.N., Wilcut, J.W. 2007. Reduced translocation is the cause of antagonism of glyphosate by msma in browntop millet (brachiaria ramose) and palmer amaranth (amaranthus palmer). Weed Technology 21:166-170.

Nandula, V.K., Reddy, K.N., Rimando, A.M., Duke, S.O., Poston, D.H. 2007. Glyphosate resistant and susceptible soybean (Glycine max) and canola (Brassica napus) dose response and metabolism relationships with glyphosate. Journal of Agricultural and Food Chemistry 55:3540-3545.

Zablotowicz, R.M., Reddy, K.N. 2007. Nitrogenase activity, nitrogen content, and yield responses to glyphosate in glyphosate-resistant soybean. Crop Protection Journal 26:370-376.

Koger Iii, C.H., Burke, I.C., Miller, D.K., Kendig, A.J., Reddy, K.N., Wikut, J.W. 2007. Msma antagonizes glyphosate and glufosinate efficacy on broadleaf and grass weeds. Weed Technology. 21:159-165.

Last Modified: 4/22/2015
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