2006 Annual Report
Several transgenic crops resistant to bromoxynil, glufosinate, and glyphosate were commercialized in the mid 1990s. However, the most successful transgenic crops (corn, cotton, and soybean) are resistant to glyphosate. Consequently, the proportion of herbicide use has shifted heavily towards glyphosate. Long-term impact of dependence on "only one herbicide" approach on shifts in weed species and selection of resistant weed populations must be addressed. Current knowledge is inadequate to address the impact of shifts in weed control technologies on the efficacy of weed control and long-term outcomes on weed populations and species shifts, and development of herbicide resistance. The problem of more weed biotypes developing resistance is expected to increase as the number of herbicides used is decreased due to increased adoption of transgenic crops resistant to glyphosate without proper rotation. Already the appearance of resistant biotypes to glyphosate heralds this problem on a global scale. No information on these biotypes has been generated nor their mechanisms for resistance.
This research contributes to weed biology and ecology component as well as weed management systems component of the National Program 304 – Crop Protection and Quarantine. This project will result in basic understanding of biological and ecological changes in weed species which will be used to develop and/or refine weed management systems in agricultural production.
This research will generate critical knowledge on the traits that lead to weediness and devise effective control measures for a number of pernicious, noxious, and invasive weeds. Farmers will benefit from efficient, economical, and environmentally safe integrated weed management systems that promote sustainable farm operations and improve farm incomes. Provide alternative strategies to control herbicide resistant weed biotypes and delay and/or prevent future occurrence. Assess the risks associated with herbicide-resistant cropping systems. Increased adoption of reduced tillage systems will decrease herbicide movement from farmlands. The public will benefit from the reduced herbicide usage and a cleaner environment.
2. Collect johnsongrass biotypes and initiate metabolism studies to determine whether biotypes have developed a greater capacity to metabolize triazine and chloroacetamide herbicides.
3. Continue 4th year study on long-term impact of glyphosate-based weed management systems in cotton, corn, and soybean.
4. Develop leaf-disc assay and rapid, non-destructive assay for screening horseweed populations for potential resistance to glyphosate. Characterize multiple glyphosate-resistant horseweed biotypes in Mississippi and Arkansas.
5. Complete investigation of mechanism of glyphosate resistance in horseweed.
Year 2 (FY 2006) 1. Complete dose-response to photosystem II herbicides in malvaceous weeds that contribute to their survival when PSII herbicides are used.
2. Continue metabolism studies to determine whether johnsongrass biotypes have developed a greater capacity to metabolize triazine and chloroacetamide herbicides.
3. Complete 5th year study on long-term impact of glyphosate-based weed management systems in cotton, corn, and soybean. Collect soil samples and determine weed seed bank.
4. Complete a 6-yr cotton/corn rotation study and document the benefits of rotation.
5. Complete the study on repeated use of glyphosate in cover crop and no-tillage based glyphosate-resistant soybean production on yield, microbial ecology, and soybean pathogens.
6. Initiate greenhouse and 15N studies to determine effect of glyphosate on N2-fixation and N assimilation in glyphosate-resistant soybean.
Year 3 (FY 2007) 1. Complete biochemical assays using photosystem II herbicides in malvaceous weeds.
2. Complete field evaluation, isozyme, and RAPD analysis and determine sesquiterpenes in purple nutsedge and their mechanisms of action on cotton.
3. Identify the mechanisms of detoxification of chloroacetamide and triazine herbicides.
4. Determine the causes for variability in growth, spread, and control of cogongrass.
5. Determine best weed management practices to reduce weed population and species shift in tillage and cover crop based glyphosate-resistant cotton.
6. Determine best winter weed management strategy for horseweed control.
7. Describe benefits of early planting cotton on weed management practices.
8. Complete studies to determine the role of AMPA in tolerance to glyphosate in other leguminous species.
Year 4 (FY 2008) 1. Complete studies on the mechanisms of detoxification of chloroacetamide and triazine herbicides in johnsongrass.
2. Complete kinetic analysis of EPSPS in glyphosate-resistant horseweed.
3. Complete glyphosate-resistant corn and glufosinate-resistant corn rotation study and document the benefits.
Year 5 (FY 2009) 1. Determine biochemical mechanisms of tolerance to PSII inhibitors in malvaceous weeds.
2. Determine sesquiterpenes in purple nutsedge and their mechanisms of action on cotton.
3. Determine the causes for variability in growth, spread, and control of pitted morningglory.
4. Complete glyphosate-resistant cotton and glufosinate-resistant cotton rotation study and document the benefits.
5. Determine if glyphosate is affecting N2-fixation and or N assimilation in glyphosate-resistant soybean.
Scientist at Southern Weed Science Research Unit conducted studies to determine if purple nutsedge biotypes have different sensitivities to glyphosate. The California biotype was most tolerant and the North Carolina and Georgia biotypes were most sensitive. There were several biotypes with intermediate sensitivity to glyphosate. The results show that control is influenced by genetic factors which differ between biotypes. Cotton sensitivity to purple nutsedge tuber and root homogenates indicated that homogenates from the Arizona biotype caused more injury in the form of stunting and chlorosis than the other biotypes. This is further indication that the biotypes have different properties.
Cogongrass is an invasive weed found in the southeastern US. Scientists at Southern Weed Science Research Unit conducted studies to determine the effect of temperature on the viability of rhizomes. Cogongrass rhizomes can be killed by exposure to temperatures above 150 C for 2 min. These studies were initiated to determine if highway construction and maintenance departments and industries could use asphalt furnaces to heat kill cogongrass. Corn and cotton seed are frequently contaminated with aflatoxins and fumonisins produced by toxigenic fungi, making them unfit for human and animal consumption. Scientists at Southern Weed Science Research Unit, Crop Genetics and Production Research Unit (CG&PRU), and Southern Insect Management Research Unit (SIMRU), Stoneville, MS have examined the effects simple agronomic practices such as crop rotation and selection glyphosate-resistant cultivars on Aspergillus flavus populations in soil and aflatoxin and fumonisin in corn and cotton seed in a 6-yr field study. A. flavus populations in surface soil were not affected by cotton-corn rotation systems. In cotton seed, aflatoxin and fumonisin levels were similar regardless of rotation and glyphosate. In corn grain, aflatoxin was above the regulatory level (20 ppb) only in GR cultivar in 1 of 4 years. Fumonisin was higher in non-GR cultivar (4 ppm) regardless of rotation in 2004. These results indicate the potential for increased aflatoxin levels (1 of 4 years) in corn.
Cotton growers across the southeastern US routinely mix glyphosate and MSMA as a post-directed application in cotton, and sometimes observe reduced weed control due to antagonism. Scientists at the Southern Weed Science Research Unit, Crop Genetics and Production Unit, Stoneville, MS, and North Carolina State University, Raleigh, NC, examined the causes for reduction in browntop millet and Palmer amaranth control by glyphosate applied with MSMA. Glyphosate has to be absorbed and translocated within the plant to be effective. Glyphosate absorption was similar but its translocation was reduced when glyphosate was applied with MSMA in both species. These results indicate that reduced translocation to be the cause of the observed antagonism of glyphosate by MSMA.
Molin, W.T. 2006. Contributions of tillage, rye cover crop and herbicide programs to weed control in glyphosate-tolerant cotton. 28th Annual Southern Conservation Systems Conference. Amarillo, TX 26-28 June, 2006, pp. 171-173.
Heatherly, L. G., S. R. Spurlock, and K. N. Reddy. 2005. Weed management in nonirrigated glyphosate-resistant and non-resistant soybean following deep and shallow fall tillage. AgProfessional, November 2005. Pages 56-60.
Bryson, C. T., K. N. Reddy, and I. C. Burke. 2006. Differential morphology of pitted morningglory populations from southern U.S. Weed Science Society of America Abstracts. 46:5.
Bryson, C. T., I. C. Burke, and K. N. Reddy. 2006. Macro-morphological analysis of pitted morningglory populations from eight southern states. Proc. Southern Weed Science Society. 59:134.
Burke, I. C., C. H. Koger, K. N. Reddy, and J. W. Wilcut. 2006. MSMA antagonizes glyphosate by reducing its translocation in Palmer amaranth. Weed Science Society of America Abstracts. 46:39.
Burke, I. C., K. N. Reddy, and C. T. Bryson. 2006. The response of pitted morningglory biotypes and weedy relatives from southern states to glyphosate. Proc. Southern Weed Science Society. 59:59.
Eubank, T. W., V. K. Nandula, D. H. Poston, C. H. Koger, and K. N. Reddy. 2006. Factors affecting germination of horseweed. Weed Science Society of America Abstracts. 46:25.
Bryson, C. T., R. Carter, and D. J. Rosen. 2006. Dispersal, biology, and control of deeprooted sedge. Proc. Southern Weed Science Society. 59:253.
Carter, R., C. T. Bryson, and D. J. Rosen. 2006. Invasive sedges: impending problems. Proc. Southern Weed Science Society. 59:254.
Rosen, D. J., R. Carter, and C. T. Bryson. 2006. The potential for spread of Cyperus entrerianus (Cyperaceae) into native habitats in the southeastern United States. Proc. Southern Weed Science Society. 59:252.
Nandula, V. K., T. W. Eubank, D. H. Poston, C. H. Koger, and K. N. Reddy. 2006. Investigations into suspected resistance of Italian ryegrass to glyphosate in Mississippi. Proc. Southern Weed Science Society. 59:172.
Nandula, V. K., D. H. Poston, C. H. Koger, and K. N. Reddy. 2006. Growth comparison of glyphosate-resistant and susceptible horseweed biotypes from Mississippi. Weed Science Society of America Abstracts. 46:26.
Nandula, V. K., D. H. Poston, K. N. Reddy, and C. H. Koger. 2006. Absorption and translocation of 14C-clethodim in wheat, bermudagrass, and glyphosate-resistant corn. Weed Science Society of America Abstracts. 46:38.
Reddy, K. N., M. A. Locke, C. H. Koger, R. M. Zablotowicz, L. J. Krutz. 2006. Conventional and glyphosate-resistant cotton-corn rotation under reduced tillage: impact on soil properties, weed control, and yield. Weed Science Society of America Abstracts. 46:46-47.
Sanyal, D., P. C. Bhowmik, and K. N. Reddy. 2006. Effect of leaf characteristics of green foxtail and barnyardgrass on primisulfuron droplet spread. Weed Science Society of America Abstracts. 46:83.
Naczi, R. F. C., B. A. Ford, and C. T. Bryson. 2006. Revision of Carex digitalis (Cypreaceae), a common sedge of North America. American Society of Plant Taxonomists. Abstract No. 547.Reddy, K.N., Bryson, C.T. 2005. Why ragweed parthenium is not a pernicious weed in the continental usa?. Proceedings Second International Conference on Parthenium Management, 2005.
Reddy, K.N., Koger III, C.H. 2003. Herbicide-resistant crops and weed management. H.P. Singh, D.R. Batish, and R.K. Kohli, eds. In: Handbook of Sustainable Weed Management, pp. 549-580, Chapter 19.
Tucker, A.O., Maciarello, M.J., Bryson, C.T. 2006. The essential oil of kyllinga odorata vahl (cyperaceae), from mississippi. Journal of Essential Oil Research, 18:381-382.
Arai, K., Hirase, K., Moriyasu, K., Molin, W.T. 2006. Effect of 4-ethyl-3-(3fluorophenyl)-1-(3-trifluoromethylphenyl) pyrrolidin-2-one on the control of graminaceous and broad-leaf weeds in cotton. Journal of Pesticide Science, 31(1), 29-34.
Reddy, K.N. 2005. Deep tillage and glyphosate reduced redvine (brunnichia ovata) and trumpetcreeper (campsis radicans) populations in glyphosate-resistant soybean (glycine max). Weed Technology 19:713-718.
Sanyal, D., Bhowmik, P.C., Reddy, K.N. 2006. Leaf characteristics and surfactant affect primisulfuron droplet spread in three broadleaf weeds. Weed Science 54:16-22.
Bryson, C.T., Fox, A.M., Byrd, J.D. 2006. Effects of temperature on wetland nightshade (solanum tampicense dunal) and its potential spread in the united states. Weed Technology 20:778-783.
Bellaloui, N., Reddy, K.N., Zablotowicz, R.M., Mengistu, A. 2006. Simulated glyphosate drift influences nitrate assimilation and nitrogen fixation in non-glyphosate resistant soybean. Journal of Agriculture and Food Chemistry. Vol 54: 3357-3364
Molin, W.T., Hirase, K. 2005. Effect of surfactants and simulated rain on the efficacy of engame formulation of glyphosate on seedling johnsongrass, prickly sida and yellow nutsedge. Weed Biology and Management 5:123-127.
Kathiresan, R.M., Koger III, C.H., Reddy, K.N. 2006. Allelopathy for weed control in aquatic and wetland systems. Inderjit and K.G. Mukerji, eds. In: Allelochemicals: Biological Control of Plant Pathogens and Diseases, Springer, The Netherlands, Vol 7, pp. 214.
Mengistu, A., Reddy, K.N. 2005. Detection of phomopsis spp on weed hosts and its pathogenicity on soybean. Seed Technology. Vol. 27: 97-100.