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United States Department of Agriculture

Agricultural Research Service


Location: Pest Management Research Unit

2007 Annual Report

1a.Objectives (from AD-416)
Objective 1: Develop and coordinate biological control programs to achieve sustained suppression of Lepidium draba L. (Brassicaceae), Centaurea spp., Hieracium spp. (Asteraceae), Tamarix spp. (Tamaricaceae), Euphorbia esula L. (Euphorbiaceae), and other invasive plants by: 1a) determining the systematics and phylogeography of target species; 1b) identifying, testing and releasing new arthropods and plant pathogens alone and in synergistic combinations; 1c) assessing rates of establishment, population growth, dispersal and impacts of agents on target weeds, native plants, and associated soil microbial communities; and 1d) integrate biological control agents with chemical, cultural and other control methods to enhance the impact of weed management programs. Objective 2: Identify key factors and mechanisms affecting the success of biological control programs and plant invasions including: 2a) genetic and phenotypic traits of target weeds that determine the success of invasive plant species in distinct ecological regions; 2b) genetic and phenotypic traits of biological control agents affecting their establishment, population growth, and impact; 2c) the biotic, edaphic, and environmental factors and mechanisms affecting weed establishment and expansion, and success of biological control agents; and 2d) integrate population information from Objectives 1 and 2 with remote sensing imagery and other spatial/temporal databases to develop spatial models of weed invasion risk.

1b.Approach (from AD-416)
Exotic invasive weeds cause about $27 billion annually in economic losses in addition to environmental impacts ranging from displacement of species of conservation concern to altered ecosystem functions. Biologically-based control methods can provide cost-effective, sustainable means of limiting the adverse impacts of invasive plants over extensive rangeland and natural areas. Our studies will focus on increasing the success of biological control efforts through better scientific understanding of: mechanisms underlying both the impact of agents and patterns of weed and agent dispersal; genetic variation within target weeds and biological control agents; evolutionary relationships of target weeds and agents; synergisms between plant pathogens, deleterious microbes, and arthropod agents; direct and indirect effects of biological control introductions on nontarget organisms in a risk analysis context; environmental factors affecting weed and biological control agent dynamics and invasion risk; and follow-on effects following suppression of weeds by biological control agents. Anticipated products of our project include new biological control agents, improved systematic and phylogeographic understanding of target weeds and control agents, improved systems for assessing and monitoring weed and insect populations; elucidation of factors and mechanisms limiting the establishment and success of biological control releases. This will benefit land managers, users of public lands, the general public, and the scientific community in the fields of invasive plant ecology, systematics and biological control.

3.Progress Report

Saltcedar (Tamarix ramosissima, T. chinensis, and their hybrids) have invaded riverways and lakeshores across the western USA and northern Mexico. In Montana, ornamental plantings of saltcedar have been suspected in starting local invasions. In comparing DNA from ornamental and nearby invasive saltcedars from Montana, North Dakota and Wyoming, we found that ornamental and invasive populations were highly dissimilar. The majority of invasive genotypes originated from invasive plants, not from ornamental plants. However, ornamental plants could not be excluded as contributors to the invasions because all DNA genotypes found in the ornamental plants were found at some frequency in the nearby invasions. These findings suggest that while ornamental saltcedars are not the sole source of invasion, they do have potential to contribute to an invasion or recreate an invasion after saltcedars are removed. These results can be used to make decisions concerning the management of ornamental saltcedar. This accomplishment addresses NP 304 (Crop Protection and Quarantine); Component 7, Weed Biology and Ecology; Problem Areas 8E, Growth, Development, and Competition, and 7B, Taxonomy and Systematics.

We developed a novel method for assessing the prerelease impact of candidate weed biocontrol agents in their native range. The method, based on recent findings on “plotless density estimators” or “nearest neighbor spatial analysis,” was developed to provide prerelease assessment of agents in their native ranges. In addition, the methods have the additional capability of evaluating agent impact on the target species, post-release. This accomplishment addresses NP 304 (Crop Protection and Quarantine), Component 9, Biological Control of Weeds, Problem Area 9A, Agent discovery and selection and risk assessment

We provided further evidence that insect/plant pathogen synergisms against perennial invasive weeds may be specific to each system. A link was established between the occurrence of root galls and accessory root disease of the perennial weed Lepidium draba and the presence of the fungal plant pathogen Rhizoctonia solani in diseased roots in the plant’s native range. The link was more precisely drawn by the finding that ten of 12 isolates belonged to a single subspecies of R. solani. This accomplishment addresses NP 304 (Crop Protection and Quarantine), Component 7, Weed Biology and Ecology; Problem Area 7B Taxonomy and Systematics, and Problem Area 9D Combining biological control agents.

We established new methods for identifying microbial species that are numerically predominant in weed rhizosphere. Methods to investigate soil aggregate community structure through culture-based methods allow a more complete picture of microbial feedback (accumulation of changes in soil or rhizosphere microbial community composition) derived from weed monocultures and the multitrophic interactions of natural enemies used to control invasive weeds. This knowledge is being integrated into strategies for restoration of native plant communities along with data on fungal community structure and overall microbial community structure assessed with culture-independent methods. This accomplishment addresses NP 304 (Crop Protection and Quarantine), Component 7, Weed Biology and Ecology; Problem Area 7F Population dynamics.

We identified and characterized differences in patterns of rhizosphere community composition of stands of leafy spurge declining in density and increasing in density. We showed that soft-rotting Erwinia species and Agrobacterium species were more frequently found to be predominant in the rhizospheres plants sampled from declining stands of leafy spurge. Such species, along with other rhizosphere bacteria of varying pathogenicity, could have the possibility of affecting attempts to restore native plant communities. This accomplishment addresses NP 304 (Crop Protection and Quarantine), Component 9 Biological Control of Weeds; Problem Area 9A Agent discovery and selection and risk assessment.

5.Significant Activities that Support Special Target Populations
Awards from American Society for Microbiology for online mentoring for the ASM Minority Mentoring Program for 2006 and 2007, both within the reporting period.

6.Technology Transfer

Number of web sites managed2
Number of non-peer reviewed presentations and proceedings27
Number of newspaper articles and other presentations for non-science audiences3

Review Publications
Caesar, A.J. 2006. Uromyces Scutellatus as a keystone species affecting Euphorbia spp. in Europe as shown by effects on density in the field. Biocontrol Science and Technology. 16:1079-1086.

Mladinich, C., Bustos, M., Ustin-Stitt, S., Root, R., Brown, K., Anderson, G.L., Hager, S. 2006. The use of Landsat 7 enhanced thematic mapper plus data for mapping leafy spurge. Rangeland Ecology and Management. 59(5):500-506.

Ustin-Stitt, S., Root, R., Brown, K., Hager, S., Mladinich, C., Anderson, G.L., Dudek, K., Ruiz-Bustos, M., Kokaly, R. 2006. Classification of leafy spurge with earth o;bserving-1 advanced land imager. Rangeland Ecology and Management. 59(5): 507-511.

Gaskin, J.F., Wilson, L.M. 2007. Phylogenetic relationships among native and naturalized hieracium (asteraceae) in Canada and the United States based on plastid DNA sequences. Systematic Botany. 32(2):478-485.

Whitcraft, C.R., Talley, D.M., Crooks, J.A., Boland, J., Gaskin, J.F. 2007. Invasion of tamarisk (Tamarix spp.) in a southern California salt marsh. Biological Invasions. 9(7):875-879.

Gaskin, J.F., Pepper, A., Manhart, J. 2006. Isolation and characterization of ten polymorphic microsatellites in saltcedars (Tamarix chinensis and T. ramosissima). Molecular Ecology Notes. 6(4):1147-1149.

Gaskin, J.F., Kazmer, D.J. 2006. Comparison of ornamental and invasive saltcedar in the USA northern Great Plains using chloroplast and nuclear DNA sequence markers. Wetlands. 26(4):939-950.

Zhang, D., Zhang, Y., Gaskin, J.F., Chen, Z. 2006. Systematics position of Myrtama Ovcz. and Kinz. based on mophological and nr DNA ITS sequence evidence. Chinese Science Bulletin. 51:117-123.

Caesar, T., Caesar, A.J., Gaskin, J.F., Sainju, U.M., Busscher, W.J. 2007. Taxonomic diversity of predominant culturable bacteria associated with microaggregates from two different agroecosystems and their ability to aggregate soil in vitro. Applied Soil Ecology. 36(1):10–21.

Ge, S., Everitt, J.H., Carruthers, R.I., Gong, P., Anderson, G.L. 2006. Hyperspectral characteristics of canopy components and structure for phenological assessment of an invasive weed. Environmental Monitoring and Assessment. 120:109-126

Last Modified: 4/16/2014
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