2007 Annual Report 1a.Objectives (from AD-416) To develop microbial herbicides to control important agricultural and invasive weeds and ecologically based weed management strategies for sustainable and organic production systems. 1b.Approach (from AD-416) A world collection of Pseudomonas syringae pv. tagetis will be screened for biological activity on Cirsium arvense to select the most efficacious strain. Molecular techniques will be used to enhance the biological activity of selected microbial biological control agents. The role of tagetitoxin in the biological activity of P. syringae pv. tagetis will be determined. A combination of descriptive research to define the impact of long-term cropping systems and component research to identify superior crop cultivars and cover crop management systems will be used to improve weed management systems. The resources of three long-term cropping systems experiments will be used to explore the influence of conventional and organic cropping systems on weed population dynamics. The influence of cover crop residue decomposition and its interactions with soil properties and seed depth on weed seedling recruitment will be determined. 3.Progress Report Vinegar application has been investigated as a method for weed management in organically managed edamame (Glycine max L.) and fall broccoli. Vinegar at 20% acetic acid concentration was applied to weeds within the crop row to achieve complete foliar coverage. Weeds between rows were controlled by cultivation. Edamame yields in treated rows were the same as yields from untreated plants. Broccoli plants treated with vinegar showed diminished leaf turger compared to the non-vinegar treated plants within 30 minutes of application. Plants treated with vinegar did not differ in size from the plants in the controls, although the lower leaves were chlorotic. Broccoli head counts were 8% higher than the unweeded controls and equivalent to the hand weeded treatment. However, total head weights and mean individual head weights were 25 and 30% lower for the vinegar treatments than for the hand weeded and unweeded controls, respectively. NP304 Component X, Weed Management Systems, Problem B, Integrated Weed Management in cropland. 4.Accomplishments Organic Farming Improves Soil Fertility Compared to Conventional No-tillage Farming. Crop production without tillage is well-known for increasing soil organic carbon while organic farming is also known to increase soil carbon and improve soils in many of the same ways as no-tillage production. However, there is skepticism whether organic farming can improve soils as well as conventional no-tillage systems because of the requirement for tillage associated with many organic farming operations. A USDA-ARS research team at the Sustainable Agricultural Systems Lab conducted a nine-year comparison of selected minimum-tillage strategies for grain production of corn, soybean, and wheat in Beltsville, Maryland, from 1994 to 2002. After nine years, corn yields were 28% lower in the organic farming system than in the standard no-tillage system, partly due to poorer weed control in the organic systems. Despite the use of tillage, higher organic inputs into the organic system led to higher soil carbon and nitrogen concentration in the organic soils compared to those in all other systems. A uniformity trial was conducted from 2003 to 2005 with no-tillage corn grown on all plots. Yield of corn grown on plots with a nine-year history of organic management were 18% higher than those with a history of conventional no-tillage production, probably as a result of higher soil carbon and nitrogen. These results suggest that organic farming systems can provide greater long-term soil improvement than conventional no-tillage systems despite the use of tillage in organic systems, however, these benefits may not be realized because of difficulty controlling weeds in organic systems. NP304 Component X. Weed Management Systems. Problem B. Integrated Weed Management in Cropland. Crops Grown in Organic Farming Systems Enhance Tolerance to Weed Competition over the Long-Term. Research at the long-term Rodale Institute Farming Systems Trial investigated the competitive relations between weeds and grain crops as part of a collaboration between Penn State, Rodale Institute, and ARS under sibling projects 1265-22000-164-01S and 1265-22000-164-02S. An analysis of weed biomass data collected since the start of the experiment in 1981 showed that weed biomass variation was greatest in the two organically managed systems and was sensitive to environmental fluctuations in rainfall timing and amount. The legacy effect from increased weed biomass in poor weed control years was negligible and did not result in immediate increases in weed biomass in subsequent years. Unexpectedly, crop yields were not significantly different among conventional and organic systems despite weed biomass averaging six times higher in the two organic systems. Experiments that were conducted within the long-term cropping systems trial in 2005 and 2006 to quantify the effects of crop and soil management practices on corn and soybean tolerance to weed competition showed that soil mediated resource availability and relative crop growth rate likely contributed to increased corn tolerance to weed competition in the organic systems. These results suggest that long-term organic farming can result in enhanced crop tolerance to weed competition as a result of integrated processes that buffer crop fitness during years of less than ideal weed control. NP304 Component X. Weed Management Systems. Problem B. Integrated Weed Management in Cropland. 6.Technology Transfer Number of web sites managed 2 Number of non-peer reviewed presentations and proceedings 5 Number of newspaper articles and other presentations for non-science audiences 7 Review Publications Casale, J., Lydon, J. 2007. Apparent effects of glyphosate on alkaloid production in coca plants grown in colombia. Journal of Forensic Science. 52:573-578. Teasdale, J.R., Abdul Baki, A.A., Park, Y.B., Rosecrance, R.C. 2007. The potential for allelopathy during decomposition of hairy vetch residue. In: Fujii, Y., Hiradate, S., editors. Allelopathy: New Concepts and Methodology. Enfield, NH:Science Publishers. p. 211-225.