2009 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.
Research goals on morningglory biotypes from several southern states was accomplished; one manuscript published and another one in review. Likewise most studies on the biodiversity of Mississippi cogongrass are completed. Sixth year study to identify benefits of herbicide rotation in glyphosate-resistant corn and glufosinate-resistant corn rotation under reduced tillage system on weeds, yield, and net returns is in progress. The area office/Delta Council request for research on narrow-row cotton production vs. traditional wide row cotton production was completed and published. A follow up weed management study on 15-inch row (row spacing x cultivars) cotton was completed. Glyphosate tolerance mechanism in Italian ryegrass was characterized and published (MSU collaboration). Studies on glyphosate-resistant mechanism in Palmer amaranth is under way (MSU collaboration). Aminomethyl phosphonic acid (AMPA), a metabolite of glyphosate, was detected in Roundup Ready (RR) soybean. Additional studies to investigate if other plant species also produce Aminomethyl phosphonic acid were completed and published. Random Amplication of Polymorphic (RAPD)DNA (Deoxyribonucleic acid) analysis of purple nutsedge populations collected across U.S. and world is completed. Two cotton production studies were extended to include management effects on reniform nematode populations. Weeds of the South, the most comprehensive book on weed identification, distribution, and toxic properties was published this year.
Narrow-row Cotton Production System. Research on narrow (38-cm) row cotton production as an alternative to wide (102-cm) row cotton production in the lower Mississippi River Delta region is limited. ARS scientists from Southern Weed Science Research Unit, Cotton Ginning Research Unit, and Application and Production Technology Research Unit, at Stoneville, MS, have conducted field studies to assess cotton canopy closure and lint yield in 38-cm and 25-cm paired rows, as compared to wide (102-cm) rows under irrigated and nonirrigated environment. Cotton canopy closed 2 to 4 weeks earlier in 38-cm and 25-cm paired rows compared to 102-cm rows. Cotton grown in 38-cm and 25-cm paired rows using lower plant populations produced higher lint yields than cotton grown in 102-cm rows, regardless of irrigation. These results indicate that cotton grown in narrow rows could reduce seed and herbicide costs and produce lint yields higher than cotton in 102-cm rows.
Cogongrass. ARS scientists at Stoneville, MS, have completed field evaluations on the growth parameters, morphology and soil requirements for cogongrass in Mississippi. Environmental conditions were determined to mask genetic variability among some cogongrass biotypes. Cogongrass grows on a wide array of edaphic characteristics. Plants thrive in soil types from all 10 physiographic regions of Mississippi, including high and low phosphorous, variable soil texture, organic matter, and chemical composition. The only soils that cogongrass does not thrive on are those that are persistently water saturated due to year round flooding.
Invasive Weeds. ARS scientists at Stoneville, MS, in collaboration with other agencies have discovered two new invasive plant species. Cuban club-rush, a non-native aquatic invasive sedge, was reported new to the Tennessee-Tombigbee River Waterway. From field observations during the past two years, this weed can form huge floating mats up to 50 meters in diameter that can impede water flow and restrict navigation. Control methods by other agencies are currently being implemented to reduce Cuban club-rush populations. Blue sedge (Carex breviculmis), a non-native sedge from Eurasia and the Indian subcontinent, was discovered in Meridian, MS, and reported new to the Americas. Field evaluations have documented its occurrence in shaded and non-shaded habitats. Blue sedge is weedy in its native range and threatens turf, garden, lawn, and fruit and nut orchards in the southeastern United States.
Field Press. A novel design for a light weight and durable field press for collecting plant samples was developed and instructions for construction were published in a botanical journal. The press is constructed of cotton cloth and velcro closures and weighs about 2 ounces. This press is easy to use in the field and aids in preservation of fragile plant parts often lost in previously conventional methods of collecting specimens with heavy boards, straps, corrugates, and blotters. Plants that wilt rapidly can be pressed immediately preserving the shape, texture and often the color that are required for proper identification and to evaluate subtle characteristics among biotypes or ecotypes of weedy and non-weedy species or species complexes. The design is currently being used by a number of scientists and students to perform field sampling to document field populations of plants in agricultural, disturbed, and native areas and has been used exclusively to evaluate biotypes for research on variable morningglory morphological characteristics.
Morphological Comparison of Morningglory Populations from the Southern U.S. Morningglories are troublesome weeds in both crop and non-crop land throughout the U.S. Weedy morningglories in the U.S. comprise several species, mostly in the genera Ipomoea and Jacquemontia. ARS scientists at Stoneville, Mississippi, have made morphological comparisons of 76 populations collected from eight southern states. Pitted morningglory complex comprise of a distinct species, pitted morningglory and a hybrid between pitted morningglory and sharppod morningglory. Hybrid morningglory possessed the most variable morphological traits followed by pitted morningglory and sharppod morningglory. Leaf shape and size, corolla color and size, and node to first internode elongation are the most useful traits to distinguish among cypressvine, hybrid, ivyleaf, palmleaf, pitted, purple moonflower, red, sharppod, and smallflower morningglories.
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Majure, L.C., Bryson, C.T. 2008. Carex breviculmis R. BR. (Cyperaceae), new to the Flora of North America. Journal of Botanical Research Institute of Texas 2:1381-1387.
Bryson, C.T., Reddy, K.N., Burke, I.C. 2008. Morphological Comparison of Morningglory (Ipomoea and Jacquemontia spp.) populations from the Southeastern United States. Weed Science 56:692-698.
Bryson, C.T., Carter, R. 2008. A novel design for a light weight and durable field press. J. Botanical Research Institute of Texas 2:517-520.
Bryson, C.T., Maddox, V.L., and Carter, R. 2008. Spread of Cuban Club-rush [Oxycaryum cubense] in the Southeastern United States. Journal of Invasive Plant Science and Management 1:326-329.
Bryson, C.T. and Carter, R. 2008. IN: Sedges: Uses, Diversity, and Systematics of the Cyperaceae. Eds., Charles T. Bryson and Richard Carter. The significance of cyperaceae as weeds. Systematic Botany, pp. 15-101.
Reddy, K.N., Burke, I.C., Boykin Jr, J.C., Williford, J.R. 2009. Narrow-Row Cotton Production Under Irrigated and Nonirrigated Environment: Plant Population and Lint Yield. Journal of Cotton Science 13:48-55.