Objective 1: Determine how crop management practices (such as cultivar selection) and abiotic factors affect weed ecology in the upper Midwest, especially in vegetable and bioenergy crops. Sub-objective 1a: Identify cover crop residues that favor edamame over the weed. Sub-objective 1b: Quantify the impact of Miscanthus invasion and removal on plant community composition. Sub-objective 1c: Quantify the role of soil environmental parameters (e.g., C, C:N and NO3-:NO2- ratios, pH, diurnal temperature variations, soil moisture) in controlling nitrification along with N-loss (denitrification) vs. N-retention (DNRA), and evaluate the link between measured N-cycle processes to weed seed germination and seedling development. Objective 2: Improve the feasibility of using multi-tactic integrated weed management approaches for regaining control of weeds with resistances to multiple herbicides, and for preventing or slowing the evolution of herbicide resistance in susceptible weed populations. Sub-objective 2a: Evaluate the impact of harvest weed seed control (HWSC) on population dynamics and management of multiple-herbicide-resistant weed genotypes in field crops. Sub-objective 2b: Develop and compare weed management systems in edamame, utilizing cover crops, herbicides, and physical weeding.
Multi-tactic integrated weed management (IWM) offers one potential approach to address the problem of multiple herbicide resistant (MHR) weeds. In IWM systems, suites of multiple complementary tactics are deployed throughout weed life cycles to increase efficacy of weed suppression, prevent survival of weeds that escape earlier management, and reduce weed populations over the long-term. In this project, we evaluate the utility of chemical, cultural, biological, and physical tactics in IWM systems for weed suppression and crop yield protection in fields with MHR weed populations. Edamame (vegetable soybean) cultivars tolerant to cover crop residues will be combined with cover crops, recently registered herbicides, and physical weeding to examine the potential of IWM in legume vegetable production systems. The contribution of improved knowledge of soil N cycling to aid better prediction of weed seedling emergence and community composition also will be evaluated in this production system. In field crops, interactions among weed seed destruction at crop harvest, cover crops, and tank mixtures of herbicides will be quantified for their impact on MHR weeds in corn and soybean. Finally, in a continuation of previous research, the impact of escaped invasive bioenergy crops on weeds of arable areas will be measured.
Vegetable crop research continued to examine opportunities for integrated weed management systems. Preliminary data from field experiments comparing weed management systems that integrate cover crops, herbicides, and physical weeding in edamame, lima bean, and snap bean have been analyzed and presented. Improving crop competitiveness in sweet corn continues to be an area of research important to unit stakeholders. Study of underlying genetic, environmental, and management drivers to crowding stress tolerance have revealed an untapped opportunity to improve profitability for both contract growers and vegetable processors. Finally, minor use research includes crop tolerance to herbicides valuable in managing multiple-herbicide-resistant weeds, including flumioxazin-based treatments for Amaranthus control in edamame and premix herbicide treatments for weed control in sweet corn. Substantial progress was made in continuing investigations of weed ecology and management, with special emphasis on understanding and responding to multiple herbicide resistance, in FY18. A device for mechanical destruction of weed seeds was tested, in combination with variable herbicide programs and tillage treatments, in a field study. This study is quantifying the impact of Harvest Weed Seed Control with the mechanical device on the population dynamics of multiple herbicide resistant weeds in central Illinois. Following a five-year study of the impact of controlled Miscanthus invasions in native plant communities in central Illinois floodplain forests and old fields, began the process of eradicating Miscanthus in summer of 2015. An ongoing monitoring and eradication program is in place to detect and control re-sprouting plants. A small number of re-sprouts were found in November 2017. These plants were flagged, and fully excavated in May 2018. Monitoring and eradication will continue for at least one more year; if no resprouts are discovered in 2019, will consider the eradication complete. N2O-reducing soil microcosms have been stably maintained and active for two years and are a unique source for cultivation of novel microbial N2O reducers from soil that have been identified through molecular signatures as distinct from conventional denitrifying bacteria. Physiological studies using non-soil reference cultures have revealed rapid N2O reduction under oxic conditions, contrasting the traditional view that such activity only occurs under anoxic soil conditions. New experiments are currently under design that builds on previous work to examine the legacy effect of soil ponding cycles on N-processes.
1. Multiple herbicide resistance traits have low fitness costs in common waterhemp. Once a weed genotype has evolved resistance to an herbicide, the amount of time that the resistance trait remains in a field depends on the ‘fitness cost’ of resistance (a decrease in the number of offspring in the absence of selection by the herbicide), compared to the non-resistant weed genotype. ARS researchers in Urbana, Illinois, in collaboration with University of Illinois scientists, found from greenhouse studies of a five-way multiple herbicide resistant population of common waterhemp, that the resistance traits all had either no, or very low, fitness costs. These results have two important lessons for farmers. First, herbicide rotation (switching among herbicides targeting these five herbicide chemistries individually over time) will not help reduce the frequency of resistance in this population. Second, management of multiple resistant populations of waterhemp is likely to benefit from integration with non-chemical control tactics, since herbicide resistance genes are likely to remain in the population for at least a decade.
2. Sweet corn processors already adapting to climate change. Increasing weather variability is straining the vegetable industry’s ability to reliably meet their production goals, by falling short in ‘bad’ years or over-producing in ‘good’ years. ‘Yield stability’ is a crop trait that favors consistent crop performance regardless of environmental conditions. After mining decades of on-farm sweet corn data throughout the U.S., an ARS scientist at Urbana, Illinois, found that sweet corn processors are beginning to favor workhorse-type cultivars (i.e. produce consistent yields across inconsistent environments) over racehorse-type cultivars (i.e. produce exceptional yields under ideal environments). The significance of this research is 1) the research is first to relate cultivar yield stability to cultivar adoption, 2) demonstrates the importance of investing in improved yield stability, and 3) provides seed companies a critical target for developing new cultivars adapted to less-than-ideal environments.
3. Busting myths about glyphosate resistant (GR) cropping systems. Glyphosate and glyphosate resistant technology dominates agronomic cropping systems throughout the U.S. Claims have been made that 1) a glyphosate toxicity in GR corn enhances its vulnerability to Goss’s wilt following glyphosate application, and 2) glyphosate causes alarming deficiencies in cationic minerals in GR corn and soybean. In multi-disciplinary, multi-location research, ARS scientists in Illinois, Maryland, and Mississippi, found no evidence to support such claims. Any potential changes to utilization of glyphosate and glyphosate resistant technology requires factual information.
4. Advances in detection of soil nitrogen cycling bacteria. Dissimilatory nitrate reduction to ammonia (DNRA) is a N-retention process that is traditionally thought to be insignificant in agricultural soils, however new molecular technology has surprisingly revealed broader diversity of soil bacteria possessing potential for DNRA. New PCR primers have been validated for detection and quantification of nrfA, the gene responsible for the DNRA process. Their use significantly improves the coverage of diverse nrfA in all environments, including a specific group of bacteria that are common to soils but previous molecular tools would not detect. DNRA has traditionally been thought to have little effect on soils with low C:N ratios, but this has been challenged with recent findings 15N studies and with the contribution of our new molecular tools, a more thorough assessment of microbial DNRA organisms and quantitation of their activities can now be conducted. These new tools now allow more thorough investigation into the contribution of DNRA in soil N-cycling to fill gaps of knowledge about N-use and mitigation of N-loss in agricultural soils.
Davis, A.S. 2018. Weed ecology and population dynamics. In: Zimdahl, J., editor. Integrated Weed Management for Sustainable Agriculture. Cambridge, UK: Burleigh Dodd Publishing. p. 1-25.
Williams II, M.M. 2018. Genotype adoption in processing sweet corn relates to stability in case production. HortScience. 52:1748-1754.
Sarmiento, C., Zalamea, P.C., Dalling, J.W., Davis, A.S., Stump, S.M., Arnold, E.A. 2017. Soilborne fungi have host affinity and host-specific effects on seed germination and survival in a lowland tropical forest. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1706324114.
Orellana, L.H., Chee-Sanford, J.C., Sanford, R.A., Loeffler, F.E., Konstantinidis, K.T. 2017. Year-round shotgun metagenomes reveal stable microbial communities in agricultural soils and novel ammonia oxidizers responding to fertilization. Applied and Environmental Microbiology. 84(2):e01646-17. doi:10.1128/AEM.01646-17.
Williams II, M.M., Bradley, C.A. 2017. Fludioxonil+Mefenoxam seed treatment improves edamame seedling emergence. HortTechnology. 27:846-851.
Williams II, M.M., Hausman, N.E., Moody, J.L. 2017. Vegetable soybean tolerance to pyroxasulfone. Weed Technology. 31:416-420.
Wu, C., Davis, A.S., Tranel, P.J. 2017. Limited fitness costs of herbicide-resistance traits in Amaranthus tuberculatus facilitate resistance evolution. New Phytologist. 74(2):293-301. doi.org/10.1002/ps.4706.
Davis, A.S., Frisvold, G.B. 2017. Are herbicides a once in a century method of weed control? Pest Management Science. 73(11):2209-2220.
Bagavathiannan, M., Davis, A.S. 2018. An ecological perspective on managing weeds during The Great Selection for Herbicide Resistance. Pest Management Science. https://doi.org/10.1002/ps.4920.
Williams, A., Jordan, N.R., Smith, R.G., Hunter, M.A., Kammerer, D.A., Kane, R.T., Koide, R.T., Davis, A.S. 2018. A regionally-adapted implementation of conservation agriculture delivers rapid improvements to soil properties associated with crop yield stability. Scientific Reports. 8:8467.
Milbrath, L.R., Davis, A.S., Biazzo, J. 2018. Identifying critical life stage transitions for biological control of long-lived perennial Vincetoxicum species. Journal of Applied Ecology. 55:1465-1475. https://doi.org/10.1111/1365-2664.13065.
Hoss, M., Behnke, G.D., Davis, A.S., Nafziger, E.D., Villamil, M.B. 2018. Short corn rotations do not improve soil quality, compared to corn monocultures. Agronomy Journal. 110(4):1274-1288.
Muthukrishnan, R., Davis, A.S., Jordan, N.R., Forester, J. 2018. Invasion complexity at large spatial scales is an emergent property of interactions among landscape characteristics and invader traits. PLoS One. 13(5):e0195892.
Park, A.G., Mcdonald, A.J., Davis, A.S. 2018. Priorities for wheat in the eastern Indo-Gangetic plains. Global Food Security Journal. 17:1-8.
Williams II, M.M. 2018. Reproductive sink of sweet corn in response to plant density and hybrid. HortScience. 53:28-32.
Crawford, L., Williams, M., Wortman, S. 2018. An early-killed rye (Secale cereale) cover crop has potential for weed management in edamame (Glycine max). Weed Science. 66(4):502-507. doi.org/10.1017/wsc.2018.5.