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United States Department of Agriculture

Agricultural Research Service

2009 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
We have made substantial progress in our work on ecological weed management in field crops. Data analysis of a three year field study of cropping system effects on long-term weed seed predation rates is nearly complete, and a manuscript has been submitted for publication. Results indicate the central importance of weed seed supply and demand in regulating weed seed predation rates and reveal a simple relationship between short-term and annual seed predation rates. Analysis of a three-year field study of cover crop termination methods on weed interference in no-till soybean is nearing completion. A rye cover crop terminated using a cover crop roller-crimper provided season-long weed suppression within a no-till soybean production system. Field studies quantifying invasion potential of biofuel feedstock candidates at sites in IL are in their second year. Preliminary results indicate that demography of the biofeedstock species Miscanthus giganteus is strongly affected by latitude of the growing location. Surveys of 175 sweet corn fields throughout Illinois, Minnesota, and Wisconsin helped identify important weed issues and gaps in current weed management systems. Analyses of these data enabled us to report major linkages among agronomic, environmental, and weed management characteristics in North American production. Specific crop canopy factors were found to improve the crop’s ability to compete with weeds, leading to identification of commercially available cultivars suited for organic sweet corn production. Separate research showed that sweet corn competitive ability improves in later crop plantings, which will be useful for adjusting weed management to local conditions. Analysis of six years of field data on sweet corn hybrid response to P450-metabolized herbicides provided further evidence of the genetic basis for varied levels of crop injury among hybrids and inbreds grown throughout North America. Study of the distance of influence of giant ragweed on ear traits of sweet corn hybrids has been completed and a manuscript is in preparation. Research on the performance consistency of reduced-atrazine treatments is drawing to a close, with one remaining field experiment with University of Guelph to complete. A multi-year seed burial study to examine giant ragweed seed decay was completed and data analyses are in progress. A controlled environment seed burial study is in progress to evaluate velvetleaf seed decay rates and to validate the use of seed conductivity as a non-destructive measure of seed viability status. Also in review is manuscript that reports bacterial community analyses of velvetleaf seed-associations, and an invited book chapter describing experimental and methodological approaches to study the microbial ecology associated with seed bank dynamics. Glycoproteins are being examined as potential antimicrobial compounds in jimsonweed seed extracts, with current efforts to establish further collaborations with natural product chemists. Molecular methods to track ammonia-oxidizing archaea and bacteria have been developed and validated for use in microcosm studies.

1. Weighing abiotic and biotic influences on weed seed predation. Reducing weed seed inputs to the soil seedbank is an important goal for integrated weed management, yet most weed management tactics are targeted at the seedling stage. Development of effective strategies for weed seedbank management will be aided by a better understanding of the ecological factors regulating weed seed predation rates in agricultural fields. Predation rates of giant foxtail, velvetleaf and giant ragweed by invertebrate and vertebrate seed predators were measured within a corn crop in Illinois. Weed seed rain of the three species, activity-density of invertebrate seed predators and weather data were measured concurrently. Structural equation models indicated that weed seed supply and seed demand by predators have much greater explanatory power for variation in seed predation rates than do weather variables or seed demise due to other factors than predation.

2. Microbial populations associated with weed seed decay. Weed seed bank persistence is a major weed management issue. The biology and ecological interactions of weeds, their seeds and soil microorganisms in a soil seedbank environment is highly complex. To examine these interactions, new and better experimental design that accounts for both seed status and microbial activities is needed. To more accurately monitor seed decay progression, several specific stages of decay were identified that will allow more meaningful interpretation of microbial succession and activities. Data collection for a multi-year giant ragweed seed study was concluded. Microbial analysis is demonstrating successional community dynamics of fungal and bacterial populations in relationship to specific periods of seed decay activity and inactivity, and soil management conditions. The study will be the first to characterize temporal microbial community changes in soil and on seeds associated with seed fate, and will be correlated to temperature, soil moisture and depth, and crop management.

Review Publications
Davis, A.S. 2008. Weed seed pools concurrent with corn and soybean harvest in Illinois. Weed Science. 56(4):503-508.

Davis, A.S., Iannuzzi, J., Renner, K., Schutte, B.J. 2008. Chemical and physical defense of weed seeds in relation to soil seedbank persistence. Weed Science. 56(4):676-684.

Guza, A.E., Renner, K.A., Laboski, C., Davis, A.S. 2008. Effect of early spring fertilizer nitrogen on weed emergence and growth. Weed Science. 56(5):714-721.

Schutte, B.J., Davis, A.S., Renner, K., Cardina, J. 2008. Maternal and Burial Environment Effects on Seed Mortality of Velvetleaf (Abutilon theophrasti) and Giant Foxtail (Setaria faberi). Weed Science. 56(6):834-840.

Davis, A.S., Luschei, E.C. 2008. Living Boundaries: Tracking Weed Seed Movement with Non-Dormant Seeds. Weed Science. 57(2):163-168.

Tracy, B.F., Davis, A.S. 2009. Weed Biomass and Species Composition as Affected by an Integrated Crop-Livestock System. Crop Science. 49(4):1523-1530.

So, Y.F., Williams, M.M. II, Pataky, J.K., Davis, A.S. 2009. Principal Canopy Factors of Sweet Corn and Relationships to Competitive Ability with Wild-proso Millet (panicum miliaceum). Weed Science. 57:296-303.

Williams, M.M. II, Davis, A.S., Rabaey, T.L., Boerboom, C.M. 2009. Linkages Among Agronomic, Environmental and Weed Management Characteristics in North American Sweet Corn. Field Crops Research. 113:161-169.

Davis, A.S., Hall, J., Jasieniuk, M., Locke, M.A., Luschei, E.C., Mortensen, D.A., Reichers, D.E., Smith, R.G., Sterling, T.M., Westwood, J.H. 2009. Weed Science Research and Funding: A Call to Action. Weed Science. 57(4):442-448.

Last Modified: 1/31/2015
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