1a. Objectives (from AD-416):
Objective 1: Measure effects of management, climate, and soil conditions on microbial processes (herbicide degradation, nitrogen cycling, and weed seedbank dynamics) in corn/soybean ecosystems. Objective 2: Evaluate the effects of management and climate change on the biology and ecology of weedy and invasive species, including potential weedy cellulosic bioenergy crops, in Midwestern cropping systems. Objective 3: Identify effective combinations of weed management components through application of both new and existing knowledge that exploit useful plant and environmental interactions in vegetable cropping systems.
1b. Approach (from AD-416):
Each objective of the proposed work seeks to advance knowledge of specific topics that directly or indirectly relate to weed-crop competition for resources, providing a basis to identify tactics of routine management that shift the competitive advantage to the crop. We examine the ecology of microorganisms and plants, and combine these efforts into a synthesis that applies research findings toward practical solutions. Each objective utilizes the whole scientific team, and regardless of scale, experiments include samples from a common group of sites, providing extensive metadata support. Studies under Objective 1 address microbial activities that are influenced by agricultural management, climate, or soil conditions. Primary climatic factors to be addressed are temperature and rainfall. In Objective 2, management and climate change will be evaluated as to effects on the biology and ecology of weedy and invasive species, including potential weedy cellulosic bio-energy crops, in Midwestern cropping systems. A particular focus will be on spatiotemporal variation in demographic parameters and population growth rates at multiple levels of scale. As a means of unifying observations, whole life cycles of weeds will be the unit of study whenever possible. Objective 3 identifies effective combinations of weed management components through application of both new and existing knowledge that exploit useful plant and environmental interactions in vegetable cropping systems.
3. Progress Report:
Degradation of the herbicide, metolachlor, in flooded soil exhibited biphasic degradation with significantly faster degradation occurring when soil microorganisms began using iron for respiration. This resulted in irreversible binding of the metolachlor residues to soil. We observed similar results with the herbicide, trifluralin in previous reports. These results suggest that the predicted increased frequency of transient flooding in the Midwest may affect the function of soil applied herbicides. We increased seed, under carefully controlled field conditions, of accessions of Palmer amaranth collected from throughout the southern U.S. for use in common garden competition experiments. Special care was taken to avoid introducing a seedbank for these species. We also monitored and measured the demography and growth of the energy crops Miscanthus giganteus and Miscanthus sinensis in old field and forest environments in central Illinois, again with special procedures to minimize invasion risk. Finally, we continued our work on the management and environmental risk factors associated with the evolution and spread of glyphosate resistant waterhemp in Illinois grain crops, beginning database construction and statistical analysis. Several experiments concerning weed management in sweet corn were conducted. Organic weed management systems in Illinois and Washington were examined, whereby combinations of competitive crop cultivars and mechanical weed management tactics were tested. In other work, integrated weed management alternatives to atrazine– the most widely used herbicide in corn production – were tested in Illinois and Minnesota. Finally, we quantified the extent to which climate region (Midwest versus Pacific Northwest), cytochrome P450 genotype in sweet corn, and herbicide tankmix influenced crop tolerance to HPPD-inhibiting herbicides. Processing pumpkin productivity and weed community characteristics also are being quantified in different production systems, including a bioenergy-vegetable double-cropping system. Biomass feedstock (rye+vetch) was fall-planted and spring-seeded; processing pumpkin is grown in different tillage and residue treatments. We have been successful in cultivating processing pumpkin, which has required some new field equipment and an aggressive fungicide application schedule. At the request of vegetable industry stakeholders, new agronomic and weed management research in vegetable soybean (edamame) is underway. One set of experiments is being used to quantify the shortcomings of current weed management systems built around the small number of herbicides being considered for use in the crop. Another set of experiments has been deployed to characterize important agronomic traits, including disease susceptibility, herbicide sensitivity, and weed suppressive traits, among new and old commercial and public cultivars.
1. Breeding considerations for safe bioenergy crop production. Herbaceous perennial grasses grown for bioenergy purposes can provide huge amounts of biomass but also have the potential to become invasive if germplasm is not selected carefully. ARS researchers at Urbana, Illinois, provided technical support for the improvement of bioenergy crop germplasm, identifying Miscanthus giganteus demographic rates associated with more rapid rates of invasive spread. The resulting simulation models of Miscanthus population dynamics and spread will provide targets for future genetic selection of Miscanthus giganteus bioenergy crop cultivars with less risk of becoming invasive. This advance will support the safe production of renewable energy, while protecting natural areas.
2. Optimal plant populations for processing sweet corn. Determining plant population density for optimal crop growth and yield is a critical decision in crop production; however, practitioners have no research-based information to support this decision in sweet corn. Plant population densities that maximized profits to the grower and vegetable processor were identified by an ARS researcher in Urbana, Illinois. By comparing results of field experiments to surveys on farms throughout the Midwest, it was learned that grower and processor gross profit margins could be improved (as much as $1,500 per acre) if higher plant populations were used with certain hybrids. The impact of this work is that it provides sweet corn growers and vegetable processors the first research-based analysis of a critical crop production decision, that is, determining the best population density for the crop. In addition, the research showed the seed industry that targeted breeding efforts to improve interplant competitive ability will improve greatly the yield potential of sweet corn. The sweet corn industry is using this research to change how it develops hybrids and grow sweet corn in North America.
3. Effective management of pests in sweet corn will benefit from an improved understanding of herbicide tolerance and disease resistance in this vegetable crop. An ARS researcher in Urbana, Illinois, in collaboration with a University of Illinois professor, summarized 27 years of data on disease resistance, and 8 years of data on herbicide tolerance in sweet corn. Key observations included 1) new hybrids have largely shifted away from sugary (su1 endosperm) to supersweet (sh2 endosperm) types; 2) the basis for sweet corn resistance to the rust Puccinia sorghi has come to be largely based on a single class of genes (Rp gene = resistance to Puccinia); and 3) there is considerable potential for improving sweet corn tolerance to herbicides, given that 20% or more of the hybrids evaluated since 2002 are able to detoxify many herbicidal compounds metabolically (using the cytochrome P450 pathway). This research has become the primary source for the sweet corn industry (growers, processors, seed companies, crop protection companies) to determine hybrid tolerance to herbicides and resistance to prevalent diseases.
Pataky, J.K., Williams, M., Headrick, M.M., Nankam, C., Du Toit, L., Michener, P.M. 2011. Observations from a quarter century of evaluating reactions of sweet corn hybrids in disease nurseries. Plant Disease. 95:1492-1506.