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United States Department of Agriculture

Agricultural Research Service

2010 Annual Report

1a.Objectives (from AD-416)
1) Gain knowledge of the ecology of important weeds in vegetable and agronomic crops to understand fundamental principles affecting weed emergence, growth, interference, seed production, and crop yield and quality;.
2)Investigate biotic and abiotic factors linked to seed predation and microbiological activities regulating weed seed and seedling survival in soil ecosystems; and.
3)Identify effective combinations of weed management components through application of new and existing knowledge and technology that exploit useful plants, natural enemies, and environmental interactions. The objectives will address the need to develop new strategies that include more efficient use of herbicides combined with increased use of alternative, biologically based weed management for agroecosystems.

1b.Approach (from AD-416)
Processes that regulate weed population density will be investigated, with particular focus 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. Important microbial seed bank relationships will be identified along with the underlying mechanisms of interactions between microbes and weed seeds. Factors that control these interactions and natural plant defenses will be examined. Long-term rates of weed seed loss due to predation will be measured and used to validate mathematical models that predict long-term predation rates from point measurements of seed predation. Attention will be paid to cropping system effects on seed predation rates, with the goal of understanding how crop habitat affects the seed-feeding activity of different seed predator taxa. Mechanisms underlying synergistic effects of combinations of weed management tactics on weeds will be examined within the context of both vegetable and agronomic production systems. Options for managing weeds in vegetables are limited, thus focused efforts using sweet corn as a model, along with application of the larger knowledge base gained from field corn and soybean studies, will be beneficial for minor crop systems. A long-term goal of this work is to develop practical guidelines, supported by ecological understanding, for creating multi-tactic weed management systems that are effective, perform consistently, and use herbicides to tune, rather than drive the system. Initially, the weed species of focus are giant ragweed, velvetleaf, giant foxtail, and wild proso millet. This research will improve our understanding of fundamental factors associated with multi-trophic processes and interactions regulating weeds throughout their life cycles. These data will contribute to systematic prediction of the impact of weeds on agronomic and vegetable crops, leading to more effective synergistic combinations of weed management tactics.

3.Progress Report
This project was terminated on February 18, 2010 and replaced with project 3611-22000-020-00D, which continues work on biologically and ecologically-based knowledge for integrated weed management systems. We have made substantial progress in our work on weed management in vegetable cropping systems. Collaboration with the ARS Vegetable and Forage Crops unit in Prosser, WA, includes investigation of conventional and organic weed management systems in snap beans; this work continues. We have made substantial progress in our work on ecological weed management in field crops. A follow-up study to specific aim 3.1 was initiated in spring 2008 to determine causes of field scale variation in yield of no-till soybean planted into a rolled rye cover crop and is now in its third and final field season. Field studies quantifying invasion potential of biofuel feedstock candidates at varying locations in IL are in their third and final year. Preliminary results indicate that demography of the biofeedstock species Miscanthus giganteus is strongly affected by latitude of the growing location. Finally, in spring 2010, we initiated epidemiological studies of agronomic management and environmental factors influencing the evolution and spread of glyphosate resistance in common waterhemp within soybean crops in central Illinois.

1. A simple relationship between short and long-term rates of seed predation. Growing evidence suggests that post-dispersal predation of weed seeds is an important ecosystem service in field crop production systems, yet measuring season-long seed predation rates remains difficult. Most measurements of seed predation are made as repeated, short-term point estimates, however these data are not well-suited to use in models of weed demography, which require season-long predation rates. Hence there is a pressing need for a means of scaling short-term measurements of seed predation to long-term predation rates. Short-term and long term weed seed predation rates were measured in parallel for two years in Urbana, IL. Comparisons of several temporal scaling approaches indicated a direct linear relationship between the sum of seeds recovered divided by the sum of seeds initially placed in the field for short and long term measurements. This finding was verified for three independent seed predation data sets for the U.S. and Europe, and thus offers a robust, straightforward solution to the problem of temporal scaling of weed seed predation rates.

2. Cover crop roller-crimper aids weed management in soybean production systems. Weed management remains the primary technical challenge in organic crop production systems. Excessive reliance upon mechanical cultivation in these systems can deplete soil organic matter, yet reduced or zero-till systems have been avoided due to lack of options for weed management in organic no-till systems. Recent improvements in cover crop roller-crimper design have opened up new possibilities for suppressing weeds in organic no-till field crop production. In field studies in Urbana, IL, soybean yield and weed biomass were similar in soybeans planted into a mechanically terminated rye cover crop, with no further weed management, compared to soybeans planted into chemically terminated rye cover crop with postemergent applications of glyphosate at labeled rates. These results offer evidence that mechanical termination of a rye cover crop using a roller-crimper can contribute to season-long weed suppression in a subsequent soybean crop managed without chemical inputs. Further work is needed to determine optimal crop sequences for producing sufficient cover crop biomass for weed suppression without pre-empting grain crop production.

3. Herbicide injury in sweet corn is more than cosmetic. Currently, some commercial sweet corn hybrids, inbreds, and breeding germplasm have mutant (i.e. non-functional) cytochrome P450 (CYP) alleles, predisposing them to herbicide injury; nevertheless, these hybrids are still grown because of their superior agronomic or horticultural traits. Our research showed that frequency of losses of marketable yield from mesotrione and nicosulfuron increase with number of mutant CYP alleles. The impact of this work is that it shows how to reduce yield losses from P450-metabolized herbicides; namely, careful consideration of the herbicide, the timing of application, and genotype at the CYP locus of the hybrids being grown.

4. Microbial populations associated with giant ragweed seed bank dynamics. Weed seed bank persistence is a major weed management issue. Data analysis of a multi-year giant ragweed seed study was concluded. One major result shows the successional fungal community dynamics associated with seeds that is distinguishes germination fate in the spring season from those seed that undergo fatal germination, the latter more closely resembling those communities associated with decayed seed through all seasons. Another result shows variations in microbial communities that correlate to different mechanisms of seed decay, rather than one main descriptive outcome of decay.

5.Significant Activities that Support Special Target Populations
Accomplishment #4 specifically supports specialty crop growers and organic farmers.

Review Publications
Davis, A.S., Raghu, S. 2010. Weighing Abiotic and Biotic Influences on Weed Seed Predation Rates. Weed Research. DOI: 10.1111/j.1365-3180.2010.00790.x

Davis, A.S., Cousens, R.D., Hill, J., Mack, R.N., Simberloff, D., Raghu, S. 2010. Screening Bioenergy Feedstock Crops to Mitigate Invasion Risk. Frontiers in Ecology and the Environment. doi:10.1890/090030

Lankau, R., Nuzzo, V., Spyreas, G., Davis, A.S. 2009. Evolutionary Limits Ameliorate the Negative Impact of an Invasive Plant. Proceedings of the National Academy of Sciences. 106:15362-15367.

Williams, M.M. II. 2009. Within-Season Changes in the Residual Weed Community and Crop Tolerance to Interference over the Long Planting Season of Sweet Corn. Weed Science. 57:319-325.

Last Modified: 1/29/2015
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