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United States Department of Agriculture

Agricultural Research Service


Location: Global Change and Photosynthesis Research Unit

2008 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
A three year study of cropping system effects on long-term weed seed predation rates was completed and highlighted the importance of different predator taxa for weed seed removal in different crops. Two studies of ecological drivers of weed seedbank persistence were completed to quantify the importance of seed mechanical and physical protection and the impact of maternal and burial environment. Articles from these studies are in press. A study of cover crop termination method on weed interference in no-till soybean was completed demonstrating that a rye cover crop terminated using a cover crop roller-crimper could provide season-long weed suppression within a no-till soybean production system. A follow-up study was initiated to determine causes of field scale variation in yield of no-till soybean planted into a rolled rye cover crop. A new investigation was started in 2008 to quantify the invasion potential of biofuel feedstock candidates at varying locations in IL. Interference studies in sweet corn resulted in three journal articles this last year. Four experiments were completed to: quantify the effects of weed interference and planting date on crop canopy development and yield; quantify variation in weed suppressive ability and crop tolerance variables among several hybrids; quantify correlations among weed suppressive ability and crop tolerance variables; and identify morphological traits associated with weed suppressive ability and crop tolerance variables. Surveys of growers’ fields with a collaborator in MN were completed, producing two journal articles in press and four in preparation. Two studies were initiated to quantify the distance of influence of giant ragweed on ear traits of sweet corn hybrids and to determine the performance consistency of reduced-atrazine treatments, the latter tested with collaborators in OR and WA. Experiments initiated in 2007 are being repeated, with an additional collaborator at the University of Guelph. Two new studies were initiated to examine interactions among weed interference, disease severity, crop population density, and crop competitive ability. Soil microorganisms that utilize seeds as nutritional resources were identified, resulting in two articles and 91 Genbank accessions. A 2007 giant ragweed seed burial study was repeated to examine soil moisture and temperature effects on seed decay. New procedures for conducting seed burial studies were established, including non-destructive methods to measure seed viability and retrieval of seeds for microbial analyses. Identification of antimicrobial compounds in seed exudates was initiated. Determination of antimicrobial activity rates in fractionated mixtures is underway. One article is in preparation. CRADA opportunities are being assessed. Effects of ALS inhibitors on ammonia-oxiders have been expanded to include archae, which were detected in a wide range of agricultural soils. New methods are being tested to track these functional populations following herbicide treatments. Research addresses NP304 Components VII (Weed Biology and Ecology), VIII (Chemical Control of Weeds), IX (Biological Control of Weeds), X (Weed Management Systems).

1. Herbicide Cross-Sensitivity. Herbicide sensitivity is considered the most serious pest management issue for sweet corn growers in North America. The unit participated in team research that determined that a single recessive gene, or very closely-linked genes, conditioned sensitivity to 11 herbicides from five unique modes of action. The gene(s) was identified as a cytochrome P450 locus on 5S. Furthermore, research showed that all 12 major sweet corn breeding programs carry the sensitivity allele, and that genotypic class (homozygous sensitive, heterozygous, homozygous tolerant) influences extent of injury from the herbicides. Given the ubiquitous production of corn in the U.S., advancement in this field has broad, large-scale impact. Technology transfer has been initiated through four technical bulletins, which have become the primary source for growers and industry to determine hybrid sensitivity. The herbicide manufacturing industry benefits by new knowledge to determine genetic material used in identifying herbicide use rates and corn breeding programs are now using this genetic basis in their approach to enhance tolerance to herbicides. Weed control options in minor crops are limited and effective herbicides are not available for many minor crops. Consequently, many growers must rely on expensive and environmentally damaging weed control practices including chemical fumigation, synthetic mulches, cultivation, and hand weeding. This accomplishment addresses NP304, Component VIII , Chemical Control of Weeds, Problem Statement IIA, Herbicide Use in Minor Crops.

2. Seed chemical and physical defense in relation to seed bank persistence. Reducing weed seed persistence in the soil 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 seed bank management will depend upon a better understanding of what causes seeds to remain alive in the soil seed bank. Chemical and physical defense of seeds of common lambsquarters, field pennycress, giant foxtail, kochia, velvetleaf and yellow foxtail were measured in relation to persistence of these seeds in the soil seed bank. Study results revealed an important weakness in the way seed defenses are constructed: weed species with transient seed banks appear to invest more in chemical defense than those species with highly persistent seed banks. As a result, seeds in the latter category are relatively more dependent upon physical seed protection for persistence in the soil seed bank, and more vulnerable to management tactics that reduce the physical integrity of the weed seed coat. This accomplishment addresses NP304, Component X-Weed Management Systems, Problem Statement IIA, Cultural and Mechanical Control.

3. Microbial populations associated with weed seed decay. Weed seed bank persistence is a major weed management issue. The annual replenishment of seeds into seed banks provides a potentially large nutritional reservoir for soil microorganisms if seeds can be readily accessed for decay. We characterized the microbial assemblages and identified more than 90 species of bacteria and more than 29 distinct fungal species on seeds of velvetleaf, wooly cupgrass, Pennsylvania smartweed, and giant ragweed. The seeds provided the major source of carbon nutrition for the seed-associated microbes and showed closely related soil microorganisms are involved in seed decay, with populations dependent on the native community in the soil. More significant, the activity may be widely distributed in different soils. The data resulted in two journal articles and 91 NCBI Genbank accessions, and provide researchers with new information for research and future development of seed bank management that utilizes naturally occurring microbiological processes to affect weed fate. This accomplishment addresses NP304 Component X, Weed Management Systems, Problem Statement IIA, Cultural and Mechanical Control.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of Web Sites Managed1
Number of Non-Peer Reviewed Presentations and Proceedings4
Number of Newspaper Articles and Other Presentations for Non-Science Audiences5
Number of Other Technology Transfer1

Review Publications
Davis, A.S. 2007. Nitrogen fertilizer and crop residue effects on seed mortality of eight annual weed species. Weed Science. 55(2):123-128.

Davis, A.S., Williams, M. 2007. Variation in wild proso millet fecundity in sweet corn has residual effects in snap bean. Weed Science. 55(5):502-507.

Liebman, M., Gibson, L.R., Sundberg, D.N., Heggenstaller, A.H., Westerman, P.R., Chase, C.A., Hartzler, R.G., Menalled, F.D., Davis, A.S., Dixon, P.M. 2008. Agronomic and economic performance characteristics of conventional and low-external-input cropping systems in the central corn belt. Agronomy Journal. 100:600-610.

Metzger, C., Boydston, R.A., Ferguson, H., Williams, M., Zack, R., Walsh, D. 2008. Interactions between population density of the Colorado potato beetle, Leptinotarsa decemlineata, and herbicide rate for suppression of solanaceous weeds. Journal of Insect Science 8:38. Available:

Nordby, J.N., Williams, M., Pataky, J.K., Riechers, D.E. 2008. A common genetic basis in sweet corn inbred C1 for cross sensitivity to multiple cytochrome P450-metabolized herbicides. Weed Science. 56:376-382.

Pataky, J.K., Meyer, M.D., Bollman, J.D., Boerboom, C.M., Williams, M. 2008. Genetic Basis for Varied Levels of Injury to Sweet Corn Hybrids from Three Cytochrome P-450 Metabolized Herbicides. Journal of the American Society for Horticultural Science. 133:438-447.

Williams, M., Boydston, R.A., Davis, A.S. 2008. Differential tolerance in sweet corn to wild proso millet (Panicum miliaceum) interference. Weed Science. 56:91-96.

Williams, M., Boydston, R.A., Davis, A.S. 2008. Crop competitive ability contributes to herbicide performance in sweet corn. Weed Research. 48(1):56-67.

Williams, M., Pataky, J.K. 2008. Genetic Basis of Sensitivity in Sweet Corn to Tembotrione. Weed Science. 56:364-370.

Chee Sanford, J.C. 2008. Weed seeds as nutritional resources for soil Ascomycota and characterization of specific associations between plant and fungal species. Biology and Fertility of Soils. 44(5):763-771.

Last Modified: 4/19/2014
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