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United States Department of Agriculture

Agricultural Research Service

2010 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
This is the final report for the project #5436-22000-013-00D “Biological Control of Invasive Plants of the Northern Great Plains” which terminated in February 2010 and is now covered under the bridging project #5436-22000-015-00D. Saltcedar invasion: We compared DNA of ornamental and nearby invasive Tamarix (saltcedar) and found the majority of invasive genotypes originated from invasive plants, not from ornamental plants. These results can be used to make decisions concerning the management of ornamental saltcedar. A DNA study of levels of hybridization in saltcedars indicated that 85% of invasive USA plants are novel hybrids, never before encountered by biological control agents in Asia. Significant progress was made in evaluating hypotheses to account for the highly variable success of Diorhabda elongata (saltcedar leaf beetle) releases for biological control of saltcedar in Montana and Wyoming. Common garden experiments have shown that beetle fitness and female oviposition preference do not vary among the broad array of genotypes found in the T. chinensis/T. ramosissima hybrid complex. However, beetle survivorship did vary with the amount of water supplied to potted saltcedar plants where survivorship was highest on plants receiving the least water. Predator censuses and exclusion experiments at field release sites showed that predation on beetle larvae is high at all sites. Hoary Cress Invasion: We investigated reproductive strategy of hoary cress (Lepidium draba), a biological control target weed that often forms large, dense patches, and found a strong bias toward patch size increase from clonal reproduction rather than from seedling recruitment. Results indicate that biological control agents that focus on reducing or eliminating seed production would do little to control the existing invasion. A strong correlation was found between damage caused by root galling weevils (Ceutorhynchus spp.) on hoary cress and the presence of the root-infecting pathogen Rhizoctonia solani. This pathogen is typically undetectable in natural soils. Hoary cress plants affected by these insect/plant pathogen interactions are stunted and chlorotic. This is strong evidence that an efficient insect/plant pathogen synergism may be the key to efficacious biological control. We also discovered a significant stem, crown and root rot disease on hoary cress: Phoma lingam. This indicates that establishment of root-feeding insects would likely invoke highly effective insect/plant pathogen synergisms at sites such as the one where this and two foliar pathogens were found. Restoration after Invasion: We began an experiment to examine how annual grasses affect perennial grass establishment in restoration seeding, and also instigated a collaboration with staff at Theodore Roosevelt National Park, ND, to examine how annual forbs may promote success in restoration seedings. These projects will be an important source of information about how we can maximize the success of restoration seedings, and will also provide basic scientific data on annual and perennial life histories, facilitation, and competition.

1. Correct identification of plant invasion. The perennial pepperweed plant invasion in the U.S. contains more than one species. Plants can be hard to identify to species using morphology alone and if the invasion is misidentified, searches for insects and diseases that can be imported to control the invasion can occur on the wrong plant species or in the wrong region of the world. ARS researchers in Sidney, MT used DNA data on perennial pepperweed plants from the USA and Asia and found that the invasion here includes two species: Lepidium latifolium and Lepidium affine. These two species have different ranges in Asia, and perhaps different insect and pathogen agents that attack them. Biological control researchers will now include both of these species in the search for agents that can control the USA invasion.

2. Manipulating maternal environments to achieve success of restoration seedings. Origin of seed used in restoration, and the environment in which it was grown (maternal environment) can have a large effect on the establishment and success of seed materials. Current success rates are very low, with only 1 to 10% of sown seeds achieving successful establishment in arid systems. Research is underway by ARS researchers in Sidney, Montana, to determine the potential for maternal effects to maximize the success of seeds used for restoration, increasing their germination percentage, their survival, and competitive ability against noxious weeds such as cheatgrass. Data from multiple experiments show that the maternal environment can impart benefits on seed progeny (i.e. drought stressed maternal plants produce drought-tolerant seeds). This information has been shared with restoration seed growers and developers and published in a leading environmental journal.

3. Extent and diversity of plant pathogens in the native range of perennial invasive weeds. For developing practices that result in effective biological control agents, ARS researchers at Sidney, Montana, published two papers characterizing two insect/plant pathogen associations and discovered another such association. These included the association of the pathogen Rhizoctonia solani with the weevil Ceutorhynchus assimilis, both of which attack the invasive weed hoary cress, as well as the characterization of R. solani isolated from spotted knapweed. The new pathogen, Colletotrichum higginsianum, was discovered for the first time occurring on hoary cress in Europe. These findings add to a growing body of evidence which supports the concept that these interactions should be accounted for in considering the potential impact of candidate biocontrol agents for invasive weeds and knowledge of them used in selection protocols (along with host range, fecundity, and other characteristics) for new agents with the greatest impact against invasive herbaceous perennial rangeland weeds.

Review Publications
Al-Shehbaz, I., Gaskin, J.F. 2010. Lepidium. In: Boufford, D., Freeman, C., Gandhi, K., Hill, M., Kiger, R., Poole, J., Schmidt, H., Shultz, L., Strother, J. and Zarucchi, J., editors. Flora of North America. New York, New York, Oxford University Press, Inc. 7:570-595.

Caesar, A.J., Caesar, T., Maathuis, M. 2010. Pathogenicity, characterization and comparative virulence of Rhizoctonia spp. from insect-galled roots of Lepidium draba in Europe. Biological Control. 52(2): 140-144.

Leger, E.A., Espeland, E.K. 2010. The shifting balance of facilitation and competition affects the outcome of intra- and interspecific interactions over the life history of California grassland annuals. Plant Ecology. 208(2):333–345.

Caesar, A.J., Lartey, R.T., Caesar, T. 2009. First Report of a Root and Crown Disease caused by Rhizoctonia solani on Centaurea maculosa in Russia. Plant Disease. 93(12): 1350-1350.

Marsico, T.D., Burt, J.W., Espeland, E.K., Gilchrist, G., Jamieson, M.A., Lindstrom, L., Roderick, G., Swope, S., Szucs, M., Tsutsui, N. 2010. Underutilized Resources for Studying the Evolution of Invasive Species During Their Introduction, Establishment, and Lag Phases. Evolutionary Applications. 3(2):203-219.

Leger, E.A., Espeland, E.K. 2010. Coevolution between Native and Invasive Plant Competitors: Implications for Invasive Species Management. Evolutionary Applications. 3(2): 169–178.

Dyer, A.R., Brown, C., Espeland, E.K., Mckay, J.M., Meimberg, H., Rice, K.J. 2010. The role of adaptive trans-generational plasticity in biological invasions of plants. Evolutionary Applications. 3(2):179-192.

Braude, S., Gaskin, J.F. 2010. Evolution and Pesticide Resistance: Examining Quantitative Trends Visually. In: Bradue, S. and Low, B.S., editors. An Introduction to Methods and Models in Ecology, Evolution, and Conservation Biology. Princeton, NJ: Princeton University Press. p. 3-11.

Gaskin, J.F. 2009. Rush Skeletonweed (Chondrilla Juncea) Management Plan for the Western United States. In: Rachel, W., Schwarzlander, M., Gaskin, J.F., Crabtree, C., editors. 1st Edition. Fort Collins, CO: Forest Health Technology Enterprise Team. pp. 117.

Espeland, E.K., Perkins, L.B., Leger, E.A. 2010. Comparison of seed bank estimation techniques using six weed species in two soil types. Rangeland Ecology and Management. 63(2): 243-247.

Espeland, E.K., Rice, K.J. 2010. Ecological effects on effective population size in an annual plant. Biological Conservation. 143(4): 946-951.

Last Modified: 12/21/2014
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