2007 Annual Report 1a.Objectives (from AD-416) Develop weed management systems for conventional peanut, organic peanut, cotton, and cucurbit crops with emphasis on reducing (or eliminating) herbicide use, altering cultural practices to reduce weed losses, and minimizing weed propagation. Develop a greater understanding of the biology of tropical spiderwort and apply that knowledge to improve weed management efficiency and maximize crop growth and yield. Develop alternative methods of weed management in cucurbit and solanaceous vegetable crops without methyl bromide fumigation by evaluating herbicides, application technology, cover crops, living mulches, solarization, and fallow tillage for pre-plant weed control. 1b.Approach (from AD-416) The commodities studied are peanut, cotton, and several vegetable crops, which are commonly grown in rotation in the southeastern coastal plain. The majority of the research will be conducted in the field; on research farms at the Coastal Plain Experiment Station and private farms which have specific weed infestations of interest. Greenhouse facilities will be fully utilized for evaluating weed seed survivability from various soil seedbanks. Growth chambers and thermal gradient germination tables will be used to evaluate base temperatures for weed seed germination, particularly tropical spiderwort. Data to be collected in these studies include weed population density, weed emergence patterns, weed growth parameters (plant height, plant width, flower number), weed fecundity, weed biomass (by species), crop growth parameters (crop height, crop canopy width, date of crop canopy closure), crop yield, and environmental factors (soil temperature, soil moisture, rainfall, photosynthetic active radiation within crop canopies). Results will be published in refereed journals, experiment station bulletins, and extension service bulletins. 4.Accomplishments Nematodes affect weed-cotton interactions: Independently, nematodes and weeds both cause significant crop yield losses. Previous studies have demonstrated that weeds can serve as alternate hosts for nematodes, while other weeds are not affected by nematodes. Commercial cotton varieties are susceptible hosts of southern root-knot nematode and suffer damage, while the weed common cocklebur is not a host. The influences of southern root-knot nematode on the interactions between cocklebur and cotton were evaluated. The presence of nematodes caused 15 to 35% more cotton yield loss at each of the cocklebur densities tested relative to the nematode-free treatments. The weed-nematode combination caused an additive reduction in cotton yield that was greater that the cotton yield loss from either pest in isolation. This indicates that crop yield losses due to weeds are underestimated in the presence of other pest types. Effective Integrated Pest Management (IPM) strategies will need to account for these interactions in order to minimize crop yield losses. This research addresses Component VII - Weed Biology and Ecology of ARS National Program 304, Problem Statement 1E: Growth, Development, and Competition. Yellow nutsedge control using summer solarization: Perennial nutsedges are among the most troublesome weeds of organic crop production and for home gardeners. Cultural and mechanical controls are marginally effective. Covering moistened seedbeds with clear polyethylene mulch during the summer months effectively controls yellow nutsedge and plant parasitic nematodes. Clear polyethylene mulch allows sunlight to heat the soil profile and when sustained for at least 90 days, reduces pest densities. These effects are seen in future crops, which often have no viable options for perennial nutsedge control. This research addresses Component 1: Pre-plant Soil Fumigation Alternatives of National Program 308 and Component X: Weed Management Systems of ARS National Program 304, Problem Statement 2A: Cultural and Mechanical Control. 5.Significant Activities that Support Special Target Populations Addressed growers at the Organic Peanut Production Field Day in Screven County, GA: This was the site of on-farm weed control research in organic peanut, in cooperation with a Certified Organic grower. The owner/operator of the certified organic farm is female. In addition, organic growers tend to be small acreage growers, which are also a targeted population. 6.Technology Transfer Number of non-peer reviewed presentations and proceedings 36 Number of newspaper articles and other presentations for non-science audiences 5 Review Publications Webster, T.M., Faircloth, W.H., Flanders, J.T., Proskto, E.P., Grey, T.L. 2007. The critical period of tropical spiderwort (Commelina benghalensis) control in peanut. Weed Science. 55:359-364. Webster, T.M., Davis, R.F. 2006. Southern root-knot nematode affects common cocklebur (Xanthium strumarium) interference with cotton. Weed Science. 55:143-146. Grey, T.L., Webster, T.M., Culpepper, A.S. 2007. Autumn vegetable response to residual herbicides applied the previous spring under low density polyethylene mulch. Weed Technology. 21:469-500. Ferrell, J.A., Murphy, T.R., Webster, T.M. 2006. Using preemergence herbicides to improve establishment of centipedegrass (Eremochloa ophiuroides) from seed. Weed Technology. 20:682-687. Culpepper, A.S., Grey, T.L., Vencill, W.K., Kichler, J.M., Webster, T.M., Brown, S.M., York, A.C., Davis, J.W., Hanna, W.W. 2006. Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) confirmed in Georgia. Weed Science. 54:620-626. Potter, T.L., Truman, C.C., Bosch, D.D., Strickland, T.C., Franklin, D.H., Bednarz, C.W., Webster, T.M. 2006. Combined Effects of Constant Versus Variable Intensity Simulated Rainfall and Reduced Tillage Management on Cotton Preemergence Herbicide Runoff. Journal of Environmental Quality. 35:1894-1902. Johnson, W.C., Mullinix, Jr., B. 2007. Yellow nutsedge (Cyperus esculentus) control with metham-sodium in transplanted cantaloupe (Cucumis melo). Crop Protection. 26:867-871. Johnson, W.C., Mullinix, Jr., B. 2005. Texas panicum (Panicum texanum) interference in peanut (Arachis hypogaea) and implications for treatment decisions. Peanut Science. 32:68-72.