2008 Annual Report
These studies benefit weed biology and ecology as well as weed management components of National Program 304 – Crop Protection and Quarantine.
The pitted morning glory complex remains troublesome despite the use of glyphosate in glyphosate-resistant (GR) cotton and GR soybean. Research has already established variable tolerance of this morning glory complex to glyphosate within GR cotton and GR soybean fields. Scientists at USDA-ARS Southern Weed Science Research Unit, Stoneville, MS, have determined that two species in the pitted morning glory complex, pitted morning glory and sharppod morning glory, and a hybrid between the two species possess more variable morphological characteristics than several other weedy morning glory species in the southeastern United States.
This research contributes to weed biology and ecology component of National Program 304 – Crop Protection and Quarantine.2. Invasive Weeds.
Water hyacinth and Cuban club-rush are non-native invasive weeds and are among the world’s worst invasive weed species. Scientists from USDA-ARS Southern Weed Science Research Unit, Stoneville, MS; USDA Southern Hardwoods Laboratory, Stoneville MS; and Mississippi State University have discovered new populations of water hyacinth in the Mississippi Delta Region and Cuban club-rush along the Tennessee-Tombigbee River Waterway. These weeds reproduce rapidly and threaten native flora and fauna, and impede navigation. Because these reports were made in a timely manner, a rapid response with control efforts was initiated in the affected areas by other agencies.
This research contributes to weed biology and ecology component of National Program 304 – Crop Protection and Quarantine.3. Aminomethylphosphonic acid accumulation in plant species treated with glyphosate. Aminomethylphosphonic acid (AMPA) is the most frequently detected metabolite of glyphosate in plants. AMPA is produced from glyphosate degradation in glyphosate-resistant (GR) soybean treated with glyphosate. AMPA accumulation causes injury to plants. Scientists at USDA-ARS Southern Weed Science Research Unit, Stoneville, MS; USDA-ARS Natural Products Utilization Research Unit, Oxford, MS; and Delta Research and Extension Center, Stoneville, MS, have investigated if other leguminous species also produce AMPA following glyphosate treatment. Studies were conducted to determine the glyphosate I50 values (rate required to cause a 50% reduction in plant growth) and to quantify AMPA concentrations in selected leguminous and non-leguminous species treated with glyphosate at I50 rate. Coffee senna was the most sensitive and hemp sesbania was the most resistant to glyphosate. AMPA was detected in six of the seven leguminous species studied. These results suggest that some leguminous species are more resistant to glyphosate than others, and a plant glyphosate oxidoreductase (GOX) may be responsible for breakdown of glyphosate to AMPA.
This research contributes to weed biology and ecology component of National Program 304 – Crop Protection and Quarantine.4. Effect of tillage, cover crops and herbicide combinations on weed populations.
Browntop millet is becoming a problem in fields after lay-by, at harvest, and during fall field preparation. Scientists at USDA-ARS Southern Weed Science Research Unit, Stoneville, MS, have investigated the development of browntop millet populations after lay-by in cotton and soybean in response to tillage, preemergence herbicide treatments and cover crops. Browntop millet establishment was curtailed by tillage, but favored in rye cover crops. Development of browntop millet populations under cotton canopy was slow requiring several years without tillage to become established. The greater vegetative biomass of some cotton varieties reduced browntop millet growth under the canopy.
This research contributes to weed management component of National Program 304 – Crop Protection and Quarantine.5. Continuous use of glyphosate may lead to increased glyphosate resistance.
Common groundsel (Senecio vulgaris) populations have been increasing in fields where continuous glyphosate applications have been made. Scientist at USDA-ARS Southern Weed Science Research Unit, Stoneville, MS, has tested common groundsel for increased tolerance to glyphosate. Tests revealed possible changes in glyphosate tolerance although the mechanism is not clear.
Early planting of cotton may be a means to reduce herbicide inputs and increase cotton yields by allowing cotton to grow during a part of the year that has longer days. Scientists at USDA-ARS Southern Weed Science Research Unit, Stoneville, MS, have investigated cotton yield responses and weed control in early and normal planted cotton. The results indicated that earlier planting did not result in increased yields or reduced herbicide usage.
This research contributes to weed management component of National Program 304 – Crop Protection and Quarantine.7. Glyphosate tolerance mechanism in Italian ryegrass populations from Mississippi.
Italian ryegrass is becoming a troublesome weed, especially as recently documented populations with increased resistance to the herbicide glyphosate have been found in Mississippi. Scientists from the Mississippi State Delta Research Center, and the USDA-ARS Southern Weed Science Research Unit and Natural Products Utilization Research Unit have studied why two populations of Italian ryegrass T1 and T2 are resistant to this herbicide. The herbicide is not metabolized in these populations, however, the herbicide remains where applied as does not move in the plant. These studies indicate that the reduced uptake and movement of the herbicide is why these invasive grasses are tolerant.
Nandula, V.K., Poston, D.H., Reddy, K.N., Koger III, C.H. 2007. Formulation and adjuvant effects on absorption and translocation of 14**c-clethodim in wheat (Tritichum aestivum L). Weed Biology and Management 7:226-231.
Reddy, K.N., Abbas, H.K., Zablotowicz, R.M., Abel, C.A., Koger III, C.H. 2007. Mycotoxin occurrence and Aspergillus flavus soil propagules in a corn and cotton glyphosate-resistant cropping systems. Journal of Food Additives & Contaminants, 24(12):1367-1373.
Mengistu, A., Castlebury, L.A., Smith, J.R., Rossman, A.Y., Reddy, K.N. 2007. Isolates of Diaporthe - Phomopsis from Weeds and Their Effects on Soybeans. Canadian Journal of Plant Pathology. 29(3):283-289.
Reddy, K.N., Bryson, C.T., Burke, I.C. 2008. Ragweed Parthenium (Parthenium hysterophorus) Control with Preemergence and Postemergence Herbicides. Weed Technology 21:982-986.
Locke, M.A., Zablotowicz, R.M., Reddy, K.N., Steinriede Jr, R.W. 2008. Tillage management to mitigate herbicide loss in runoff under simulated rainfall conditions. Chemosphere. 70:1422-1428.
Reddy, K.N., Rimando, A.M., Duke, S.O., Nandula, V.K. 2008. Aminomethylphosphonic acid accumulation in plant species treated with glyphosate. Journal of Agriculture and Food Chemistry 56:2125-2130.
Sanyal, D., Bhowmik, P.C., Reddy, K.N. 2008. Effect of surfactants on primisulfuron activity on barnyardgrass and green foxtail. Weed Biology and Management 8:46-53.
Nandula, V.K., Reddy, K.N., Poston, D.H., Rimando, A.M., Duke, S.O. 2008. Glyphosate-tolerance mechanism in Italian ryegrass (Lolium multiflorum) from Mississippi. Weed Science 56:344-349.
Bryson, C.T. 2007. Carex opaca (Hermann) P.E. Pothrock & Reznicek (CYPERACEAE) new to North Carolina. Castanea, Vol. 72, No. 2, pp. 123.
Skojac, Jr, D.A., Bryson, C.T., Walker, C. 2007. Noteworthy Collections from the Yazoo-Mississippi Delta Region of Mississippi. Journal of the Botanical Research Institute of Texas 1:769-775.
Carter, R., Bryson, C.T., Darbyshire, S.J. 2008. Preparation and Use of Voucher Specimens for Documenting Research in Weed Science. Weed Technology 21:1101-1108.
Bryson, C.T., Byrd, J.D. 2007. Biology, Reproductive Potential, and Winter Survival of Tropical Soda Apple (Solanum viarum). Weed Technology 21:791-795.