2013 Annual Report
1a.Objectives (from AD-416):
1. Develop integrated systems of weed management for organic agronomic and vegetable cropping systems, such as peanut, cotton, cucurbits and dry bulb onion respectively, in the southeastern coastal plain.
2. Identify the ecological and edaphic factors affecting the reproduction, spread, and survival of invasive, herbicide-reistant, and herbicide tolerant weed pests of agronomic and vegetable crops in the southeastern coastal plain, including, but not limited to pigweeds, common bermudagrass, and perennial nutsedges.
3. Combine effective chemical and cultural control measures into integrated systems for the management of key species of herbicide resistant and invasive weeds of agronomic and vegetable crops in the southeastern coastal plain, such as pigweeds and Benghal dayflower.
1b.Approach (from AD-416):
Research will be conducted to determine weed management practices that will: A) Manage weeds without conventional herbicides in organic systems and B) reduce reliance on a dwindling number of herbicide tools in conventional systems.
Conventional weed management systems rely heavily on herbicides to minimize crop yield losses associated with weeds. Organic cropping systems have few approved herbicide options, and must rely primarily on weed control from cultural and mechanical practices. The occurrence of herbicide-resistant weeds has limited the efficiency of many herbicides in conventional systems. Studies will be initiated to evaluate a multi-tactic approach to managing weeds with a reduced reliance on herbicide tools. In the first objective, integrated weed management systems will be developed in organic agronomic and vegetable cropping systems. Cultural and mechanical weed management strategies will be employed to prevent seedling establishment and reduce propagule persistence in the soil. The second objective will determine the factors that affect the reproduction and persistence of herbicide-resistant and herbicide tolerant weed pests. Specific studies will include the effect of cover crops on weed establishment, growth, and fecundity, as well as determining the factors that affect persistence of the soil seedbank. The third objective is to combine effective chemical and cultural control measures into integrated systems for the management of key weed species. Weed growth and reproduction as affected by crop stand and presence of cover crops will be evaluated. Ultimately fulfillment of these objectives will improve grower profitability and reduce reliance on a limited set of herbicide resources that are rapidly declining in efficiency.
Research is focused on understanding interactions between weeds and crops to improve weed management in various cropping systems. Diversity of cropping systems and weeds in the research project reflect the landscape of Georgia and the Southeast U.S. Glyphosate-resistant Palmer amaranth has become the most troublesome weed of cotton in the Southern U.S., costing Georgia growers over $110 million/year. Palmer amaranth has developed resistance to four different herbicide mechanisms of action. A multi-faceted program that does not solely rely on herbicides to manage this weed is being developed. High biomass rye residues in cotton and other winter cover crops are likely components of this management program. Prior to cotton planting, the cover crop is rolled flat, forming a mat that the small-seeded Palmer amaranth seeds cannot emerge through. Preliminary data indicated that soil inversion from a moldboard plow in long-term reduced tillage systems will bury surface weed seed too deep for them to emerge and bring up weed-free soil from deep in the profile. Long-term research trials were initiated in 2011 to evaluate this hypothesis. Further study of the factors that affect seed production and seed return to the soil profile will continue. The search for effective herbicide tools for purple nutsedge control in vegetables continues in the absence of methyl bromide. Herbicides that affect tuber production have been identified and their effects quantified, providing growers with additional tools for managing this perennial weed. The need for alternative biofuel crops has been undertaken. Based on preliminary studies, it appears that energy beet (industrial sugar beet varieties) has potential as a winter crop in the Southern region.
Weed management research in organic cropping systems is a significant component of this research project. Research effort has focused on weed management in organic production of peanut, Vidalia® sweet onion, and cucurbit vegetable crops. In-row weed control in organic peanut production remains difficult and problematic. There are references in older scientific literature to cultivation perpendicular to the row in cotton. At the time of that research, selective herbicides had not been developed and perpendicular cultivation was a practice that sacrificed cotton stand for improved weed control in the row. Cotton has the ability to compensate for stand reductions. This concept was investigated in organic peanut using a tine-weeder for cultivation. Weed control was slightly improved by combinations of early season perpendicular cultivation and traditional parallel cultivation. However, damage to the peanut stand from perpendicular cultivation negated benefits of improved weed control. Peanut has limited ability to compensate for stand reduction and while perpendicular cultivation targeted in-row weeds, yield potential was significantly reduced. There is no tangible reason to use perpendicular cultivation in organic peanut production and these results are further evidence that uniformity and integrity of the peanut stand is an essential cultural practice.
Improving performance of herbicide derived from natural products. Cultivation is a proven component in the management of weeds in organic Vidalia sweet onion production. However, delays in the initial cultivation due to wet soils reduce the overall effectiveness of cultivation. In cases where initial cultivation is delayed, improved performance using herbicides derived from natural sources would be useful. These herbicides include clove oil, d-limonene, and pelargonic acid. Herbicides derived from natural sources were found to be much more efficacious when applied using a sprayer calibrated for a high output (>50 gal./A) compared to sprayers with a normal calibration (approximately 25 gal./A). When herbicides derived from natural products were applied in this manner, early season weed control was significantly improved and was synergistic with cultivation using a tine weeder.
Intense cultivation in organic peanut does not increase disease incidence. Intense cultivation is a proven weed control practice in organic peanut production. However, intense cultivation for weed control is contradictory to conventional and historical peanut production philosophy which correlates cultivation with increased disease incidence. Multi-disciplinary studies have shown that intense cultivation in organic peanut does not cause increases in soil-borne diseases. This is due to different cultivation implements (tine weeder vs. sweep cultivator that displaces more soil) and use of disease resistant peanut cultivars in organic production systems. While these studies targeted organic peanut production systems, the results are equally applicable to conventional production systems. With increases in herbicide resistant Palmer amaranth in the region, more of the conventional peanut acreage is being cultivated to control weed escapes. Results from these studies help allay concerns of increased disease epidemics since peanut cultivars are the same between conventional and organic production systems.
A potential Southern winter cash crop: energy beets. The broad search for crop-based fuel alternatives has involved many potential plant species, including those with non-desirable environmental characteristics. Beets are an ideal crop for biofuel production in the southern U.S. An established crop in other regions of the U.S., there is improved beet germplasm, pest management options, and knowledge of necessary agronomic practices exists. In addition, beet is an annual crop grown in the winter when most fields are dormant, allowing growers to work this into an existing summer crop rotation. ARS researchers in Tifton, Georgia have determined that autumn planted beets will produce between 60 and 120 Mg/ha of root biomass when harvested the following spring, beginning in April and continuing through June. Beets will continue to increase in size and biomass while in the ground; there is no physiological maturity, allowing for “harvest on demand” supply to processing facilities. Unlike the cellulosic biofuel crops, the sugars within the root do not require enzymatic conversion and can produce up to an estimated 1270 gal/a of ethanol or 660 gal/a of butanol (to be used for aviation fuel). Continued refinement of adapting management practices of this summer-grown crop of the upper Midwest to a winter-grown crop in the South are still occurring.
Use of herbicides during establishment of Miscanthus giganteus, a potential biofuel crop. Miscanthus giganteus has potential as a bioenergy crop due to its significant yield advantage compared to other grass bioenergy species. Grass weed control during crop establishment has been a major challenge in M. giganteus management as there are no herbicides currently registered for use in M. giganteus in the U.S. Researchers from the University of Georgia in cooperation with ARS scientists in Tifton, Georgia evaluated potential herbicide combinations during establishment of M. giganteus from vegetative rhizomes. These data indicated that selected herbicides can be utilized for establishment of M. giganteus from vegetative rhizomes. Further experiments are needed in field trials to evaluate establishment success and weed control spectrum utilizing these herbicides. Moreover, considering the invasive potential of M. giganteus, several POST herbicides evaluated in this study like fluazifop, pyrithiobac and sulfometuron may be viable options to control this species outside of desired plantings.
Reducing potential weed populations by hindering tuber production. Purple nutsedge is the most troublesome weed of vegetable crops in the Southeast U.S. and one of the weaknesses of many of the methyl bromide alternatives that have been implemented. ARS researchers in Tifton, Georgia evaluated the influence of six rates of the herbicide halosulfuron on purple nutsedge tuber production. A single purple nutsedge tuber allowed to grow for 13 weeks in a field plot produced 530 tubers. At the registered use rate in vegetables, purple nutsedge tuber numbers and biomass were reduced 79 and 93%, respectively, relative to the non-treated control. In addition, the viability of these tubers was reduced 78%. As a result, the number of viable tubers was reduced 95% compared to the non-treated control. The prolific tuber production will allow for re-establishment of purple nutsedge populations from one season to the next. Halosulfuron may allow growers to begin to lower their purple nutsedge tuber population and improve weed control.
Purple nutsedge tubers lose viability after 33 months of burial. Purple nutsedge, the most troublesome weed of vegetables in the Southeast U.S., reproduces through tubers. The persistence of purple nutsedge tubers in the soil affects future weed populations. ARS researchers in Tifton, Georgia buried purple nutsedge tubers at two depths and exhumed the tubers at regular intervals to evaluate tuber viability and persistence in the soil. Preliminary results suggest that purple nutsedge tubers remain intact during the first year of burial, but fall to less than 50% viability after 18 months and have less than 1% viability by 33 months. While tubers represent a large source of energy reserves with multiple potential buds that allow for regrowth when shoots are removed, it appears that their persistence in the soil seedbank is relatively short-lived compared to seeds.
Biodegradable mulching material made from cotton gin trash. Commercial watermelon and cantaloupe production systems use transplants grown on seedbeds covered with thin-film mulch. It is costly to procure, remove from the field, and dispose thin-film mulches. Alternative biodegradable mulching materials will eliminate the cost associated with removal and disposal. ARS researchers in Tifton, Georgia evaluated an alternative mulching material made from processed cotton gin trash that uses pressure and heat to loosely bond cotton gin trash into a mat 1 cm thick. This material was successfully applied using conventional mulch application equipment and adequately suppressed Palmer amaranth when treated post-application with linseed oil or black latex paint. The rolled cotton fiber mat made from cotton gin trash offers great potential as an alternative mulching material since it is fully biodegradable, made from a common waste material, and serves as a value-added product to the cotton industry.
Prostko, E., Grey, T., Webster, T.M., Kemerait, R. 2012. Peanut tolerance to pyroxasulfone. Peanut Science. 38:111-114.
Sosnoskie, L.M., Webster, T.M., Macrae, A.W., Grey, T.L., Culpepper, A.S. 2012. Pollen-mediated dispersal of glyphosate-resistance in Palmer amaranth under field conditions. Weed Science. 60:366-373.
Riar, M.K., Webster, T.M., Brecke, B.J., Jordan, D.L., Burton, M.G., Rufty, T.W. 2012. Benghal dayflower (Commelina benghalensis) seed viability in soil. Weed Science. 60:589-592.
Sosnoskie, L., Webster, T.M., Culpepper, A. 2013. Glyphosate resistance does not affect Palmer amaranth seedbank longevity. Weed Science. 61:283-288.
Ward, S.M., Webster, T.M., Steckel, L.E. 2013. Palmer amaranth: A review. Weed Technology. 27:12-27.
Prostko, E.P., Kemerait, R.C., Webster, T.M. 2012. Georgia-06G, Florida-07, and Tifguard response to chlorimuron. Weed Technology. 26:429-431.
Wallace, R.D., Grey, T.L., Webster, T.M., Vencill, W.K. 2013. Increased purple nutsedge (Cyperus rotundus) tuber sprouting with diurnally fluctuating temperatures. Weed Science. 61:126-130.
Dutta, B., Gitaitis, R., Lewis, K., Booth, C., Langston, D., Webster, T.M., Riner, C., Edenfield, J. 2013. New report of Lolium multiflorum and Rumex crispus as weed hosts of epiphytic populations of Psuedomonas sp., causal agent of yellow bud in onion in Geogia, USA. New Disease Reports. 27:18.
Johnson, III, W.C., Boudreau, M.A., Davis, J.W. 2012. Cultural practices to improve in-row weed control with cultivation in organic peanut production. Weed Technology. 26:718-723.
Johnson, W.C., Boudreau, M.A., Davis, J.W. 2012. Combinations of corn glutel meal, clove oil, and sweep cultivation are ineffective for weed control in organic peanut production. Weed Technology. 27:417-421.