Progress 07/12/05 to 02/16/10
Outputs
Progress Report 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. 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. 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. Accomplishments 01 Correct identification of plant invasion. The perennial pepperweed plant invasion in the U.S. contains more than one species. Plants can be hard 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 wron 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 contro researchers will now include both of these species in the search for agents that can control the USA invasion. 02 Manipulating maternal environments to achieve success of restoration seedings. Origin of seed used in restoration, and the environment in whi 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 i 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. 03 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 t pathogen Rhizoctonia solani with the weevil Ceutorhynchus assimilis, bot 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 biocontro 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.
Impacts
(N/A)
Publications
- 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 & 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.
- 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. Vol. 7. p. 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- 148.
- 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. 208:333�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 trans-generational plasticity in biological invasions of plants. Evolutionary Applications. 3(2):179-192. doi:10.1111/j.1752- 4571.2010.00118.x
- 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.
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Progress 10/01/08 to 09/30/09
Outputs
Progress Report 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. 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. Significant Activities that Support Special Target Populations Taxonomy: Perennial pepperweed (Lepidium latifolium) and dalmatian toadflax (Linaria dalmatica) are major invasive plants in western states, and in both cases, it is unclear to botanists worldwide which of the many species names they correlate with in Eurasia. Without correct knowledge of our invasives� names, it is difficult to design a biological control program and search for biological control agents that will attack our invasion. We collected and started analysis of DNA from USA and Asia in order to compare DNA and answer these taxonomic questions. Saltcedar (Tamarix spp.) biological control: A new agent (galling moth) was imported to USA to begin rearing and host-specificity studies. Survival during shipment needs to be improved. Whitetop (Lepidium draba): We began rearing studies to see if a newly proposed weevil agent will reproduce with an existing, similar cabbage seed pod weevil, which would preclude its use as a biological control agent. New soilborne diseases of white top: We discovered a significant stem, crown and root rot disease on whitetop: 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.
Impacts
(N/A)
Publications
- Gaskin, J.F., Kazmer, D.J. 2008. Introgression between saltcedars (Tamarix chinensis and T. ramosissima) in the USA invasion. Biological Invasions. 11(5):1121-1130.
- Ayres, D., Ryan, F.J., Grotkopp, E., Bailey, J., Gaskin, J.F. 2008. Tumbleweed (Salsola, secion Kali) Species and Speciation in California. Biological Invasions. 11(5):1175-1187.
- Caesar, A.J., Lartey, R.T. 2008. First report of crown gall caused by Agrobacterium tumefaciens on Euphorbia esula/virgata in Europe. Plant Disease 92(12):1710-1710.
- Caesar, A.J., Lartey, R.T., Berner, D.K., Souissi, T. 2009. First report of leaf spot caused by Cercospora bizzozeriana on Lepidium draba in the United States. Plant Disease. 93(1):108-108.
- Shi, W., Pan, B., Gaskin, J.F., Kang, X. 2009. Morphological Variation and Chromosome Studies of Calligonum mongolicum and C. pumilum (Polygonaceae). Nordic Journal of Botany. 27(2):81-85.
- Gaskin, J.F., Wheeler, G.S., Purcell, M., Taylor, G. 2009. Molecular evidence of hybridization in Florida's sheoak (Casuarina spp.) invasion. Molecular Ecology. 18(15):3216-3226.
- Friedman, J., Rolle, J., Gaskin, J.F., Pepper, A., Manhart, J. 2008. Latitudinal variation in cold hardiness in introduced Tamarix and native Populus. Evolutionary Applications. 1:598-607.
- Caesar, T., Busscher, W.J., Novak, J.M., Gaskin, J.F., Kim, Y. 2008. Effects of Polyacrylamide and Organic Matter on Microbes associated to Soil Aggregation of Norfolk Loamy Sand. Applied Soil Ecology. 40:240-249.
- Caesar, A.J., Lartey, R.T. 2009. First Report of a Leaf Spot Caused by Alternaria brassicae on the Invasive Weed Lepidium draba in North America. Plant Disease. 93(8):846-846.
- Caesar, T., Lartey, R.T., Solberg Rodier, L.L., Caesar, A.J. 2009. Effects of Basidiomycete laccase on Cercosporin. Journal of Plant Pathology. 91(2) :347-355.
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Progress 10/01/07 to 09/30/08
Outputs
Progress Report 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. 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. Significant Activities that Support Special Target Populations Restoration of rangeland following biological control: Native species are often used to restore rangeland after removal of invasive species. We performed research on plant diseases affecting transplanted native species in Theodore Roosevelt National Park. Studies thus far have identified soilborne fungi that are highly pathogenic to native rangeland species. Biological control using plant pathogens: A leaf spotting disease of invasive hawkweed, caused by the fungus Cercospora bizzozeriana, isolated from Europe, was identified and tested for pathogenicity and host range in 2007-2008. A site with a population of hawkweed with heavy occurrence of a rust disease was located in France, from which rust spores will be obtained for pathogenicity tests against U. S. populations of hawkweed. The first occurrence of the leaf and stem pathogen, Alternaria brassicae, found on hoary cress was also found in late 2007. Pathogenicity and comparative virulence tests of a soilborne fungus, Rhizoctonia solani, associated with galls produced by larvae of an insect specific to hoary cress, were completed and analyzed. The first occurrence of Rhizoctonia solani on a North American population of hoary cress was found in June 2008. A new pathogen of hoary cress was also found, Colletotrichum higginsianum, causing stem cankers. Pathogenicity tests documenting the occurrence of a root disease in Europe, crown gall of leafy spurge, were completed in April 2008. NP 304 Crop Protection and Quarantine, Component IX/d Biological Control of Weeds; Combining Biological Control Agents. Weed studies: Collections were made for understanding relationships of Lepidium, a genus which contains 4 important invasive species in the USA. A study of levels of hybridization in Tamarix (saltcedar) indicated that 85% of invasive USA plants are hybrids. With USGS researchers, we found that frost sensitivity appears to be a factor limiting northward expansion of saltcedar. There is strong inherited latitudinal variation in cold hardiness for both Tamarix species. Hybridization between these two saltcedar species may have introduced the genetic variability necessary for rapid evolution of the latitudinal gradient in cold hardiness. NP 304 Crop Protection and Quarantine, Component VII/b Weed Biology and Ecology; Taxonomy and Systematics. Biological control using insects: 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 (Tamarix spp. and their hybrids) 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. NP 304 Crop Protection and Quarantine, Component IX/c: Biological Control of Weeds; Field Evaluation.
Impacts
(N/A)
Publications
- Ward, S., Gaskin, J.F., Wilson, L. 2008. Ecological genetics of plant invasion: What do we know? Journal of Invasive Plant Science and Management. 1:98-109.
- Caesar, T., Caesar, A.J., Gaskin, J.F., Sainju, U.M., Stevens, W.B. 2008. Ecology and function of culturable microbes in soil aggregation. In: Tian- Xiao Liu, editor. Soil Ecology Research Developments. Hauppauge, NY:2007 Science Publishers, Inc. p. 121-138.
- Natale, E.S., Gaskin, J.F., Zalba, S.M., Celballos, M., Reinoso, H.E. 2008. Especies del g�nero Tamarix (Tamaricaceae) invadiendo ambientes naturales y seminaturales en Argentina. Bolet�n de la Sociedad Argentina de Bot�nica. 43(1-2):1-9.
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Progress 10/01/06 to 09/30/07
Outputs
Progress Report 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. 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. Accomplishments 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. 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. Technology Transfer Number of Web Sites managed: 2 Number of Non-Peer Reviewed Presentations and Proceedings: 27 Number of Newspaper Articles,Presentations for NonScience Audiences: 3
Impacts
(N/A)
Publications
- 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
- 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. The use of earth observing-1 hyperion data for mapping leafy spurge. 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. 9:875-879. Available: http://www.springerlink. com/content/b5557423270ug210/fulltext.pdf.
- 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.
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Progress 10/01/05 to 09/30/06
Outputs
Progress Report 1. What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? Why does it matter? 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. This project focuses 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; environmental factors affecting weed and biological control agent dynamics and invasion risk; and follow-on effects following suppression of weeds by biological control agents. The project has two specific objectives: Objective 1: Develop and coordinate biological control programs to achieve sustained suppression of Lepidium draba L. (Brassicaceae), Centaurea spp. and 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. 1d) Integrate biological control agents with chemical, cultural and
other control methods to enhance the impact of weed management programs. Objective 2 focuses on identifying 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. 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. This project will contribute to NP 304 (Crop Protection and Quarantine), component 7 (Weed Biology and Ecology) and component 9 (Biological Control of Weeds). This project will also impact NP 205 (Rangeland, Pasture and Forages), component 1 (Ecosystems and Their Sustainable Management), and component 5 (Integrated Management of Weeds and Other Pests). 2. List by year the currently approved milestones (indicators of research progress) 2005/Year 1 Publish hybridization study of Tamarix ramosissima and Tamarix aphylla. Publish population structure study of Lepidium draba. Molecular systematics of Tamarix-feeding beetles in the genus Diorhabda -
Data collection Host specificity testing of Ceutorhynchus assimilis - Data collection Post-release studies on Diorhabda dispersal, population growth, and impact on target and nontarget plants - Data collection Influence of Tamarix genotype on Diorhabda fitness parameters - Data collection Effects of Wolbachia on Aphthona nigriscutis sex ratios - Data collection Field tests of putative aggregation pheromone in A. nigriscutis and A. lacertosa - Data collection Initiate determination of important plant pathogens associated with white top in its native and invaded ranges including Kochs postulates for these. Identify and survey overseas areas with endemic leafy spurge rust and hawkweed leaf smut. Select sites with new and long-term infestations of salt cedar or white top, and design sampling scheme. Collect soil samples from sites with new and long-term infestations of white top or salt cedar. Isolate and test predominant or typical isolates of microbes on white top or salt cedar from
long- or short-term infestations, and assess feedback effects. Select sites with established insect biological control agent populations yet lacking significant impact on stand density. Collect and use aerial hyperspectral imagery data to develop algorithms that reduce positional errors, cross noise and climatic/atmospheric differences in rangeland images to better detect and map weed invasions. Publish preliminary work on the dynamics of biological control agent effectiveness for controlling Tamarix. Initiate identification of remote sensing data needed to temporally evaluate rangeland trends. 2006/Year 2 Publish clonal reproduction study of Lepidium draba. Publish study of Tamarix population structure across North America. Molecular systematics of Tamarix-feeding beetles in the genus Diorhabda - Data collection, analysis and publication Host specificity testing of Ceutorhynchus assimilis - Data collection Post-release studies on Diorhabda dispersal, population growth, and impact on
target and nontarget plants - Data collection, analysis and publication Influence of Tamarix genotype on Diorhabda fitness parameters - Data collection, analysis and publication Effects of Wolbachia on Aphthona nigriscutis sex ratios - Analysis and publication Field tests of putative aggregation pheromone in A. nigriscutis and A. lacertosa - Analysis and publication Impact of C. assimilis on Lepidium fitness parameters - Data collection Assess overseas sites for leafy spurge rust and hawkweed leaf smut severity, pervasiveness and impact on stands of target species; collect soil samples and extract inoculum. Extract leafy spurge rust and hawkweed leaf smut inoculum and test for infectivity on respective hosts Initiate tests of resistance of knapweed species from foreign and domestic sources with varying ploidy levels, unique haplotypes or wide geographic origin to Agrobacterium tumefaciens. Collect and use aerial hyperspectral imagery data to refine and validate algorithms that reduce
positional errors, cross noise and climatic/atmospheric differences in rangeland images to better detect and map weed invasions. Publish study results on the dynamics of biological control agent effectiveness for controlling Tamarix. Continue identification of remote sensing data needed to temporally evaluate rangeland trends, and collect and format datasets. 2007/Year 3 Publish Lepidium systematics study. Publish hybridization study of whitetop species (Lepidium spp.). Molecular systematics of Tamarix-feeding beetles in the genus Diorhabda - Data collection, analysis and publication Host specificity testing of Ceutorhynchus assimilis - Data collection, analysis and publication Post-release studies on Diorhabda dispersal, population growth, and impact on target and nontarget plants - Data collection, analysis and publication Influence of Tamarix genotype on Diorhabda fitness parameters - Analysis and publication Field tests of putative aggregation pheromone in A. nigriscutis and A.
lacertosa - Analysis and publication Impact of C. assimilis on Lepidium fitness parameters - Data collection Complete Kochs postulates for selected white top pathogens. Test preliminary protocol for leafy spurge rust and hawkweed leaf smut using soil samples from initial sites. Extract leafy spurge rust and hawkweed leaf smut inoculum and test for infectivity on respective hosts Complete of leafy spurge rust and hawkweed leaf smut infectivity tests and prepare publications. Analyze data and prepare publications on enhancing insect-pathogen synergy for weed biological control. Select white top sites to study integrating plant pathogens with reduced herbicide levels. Complete survey for crown gall bacterium in European stands of knapweed species Collect and use aerial hyperspectral imagery data, using sensors capable of multi-state regional coverage, to refine and validate algorithms that reduce positional errors, cross noise and climatic/atmospheric differences in rangeland images to
better detect and map weed invasions. Publish study results on the dynamics of biological control agent effectiveness for controlling Tamarix. Begin temporal analysis of datasets to evaluate rangeland conditions, trends and risk to weed invasion. Initiate integration of remote sensing data with ecological models. 2008/Year 4 Publish Centaurea of North America systematics study. Publish Hieracium of North America systematics study. Molecular systematics of Tamarix-feeding beetles in the genus Diorhabda - Analysis and publication Host specificity testing of Ceutorhynchus assimilis - Data collection, analysis and publication Post-release studies on Diorhabda dispersal, population growth, and impact on target and nontarget plants - Data collection, analysis and publication Impact of C. assimilis on Lepidium fitness parameters - Data collection Complete Identification, characterization and comparison of virulence of white top pathogens. Test white top pathogens in combination with other
plant pathogens to assess synergistic interactions. Prepare publications on changes in microbial communities due to long-term presence of perennial weeds. Complete analysis of host range data and other phenotypic traits of microbes isolated from long and short-term saltcedar or white top infestations, and correlate with microbial community structure. Complete documentation of impact of supplementary plant pathogen releases at sites with insect biological control agents. Complete assessment of impact of herbicide and plant pathogens on white top stand density or biomass. Analyze results of herbicide and plant pathogen interaction on white top populations. Prepare publication on impact of herbicide and plant pathogen interactions on white top populations. Complete assessment of resistance of various populations of knapweed species to crown gall bacteria (Agrobacteriium tumefaciens) strains in the greenhouse. Assess knapweed populations for their level of catechin production. Complete
study on reducing errors in remote sensing data to enhance rangeland management and monitoring, and publish results. Publish study results on the dynamics of biological control agent effectiveness for controlling Tamarix. Continue temporal analysis of regional datasets to evaluate rangeland conditions, trends and risk to weed invasion. Publish preliminary results of rangeland monitoring. Continue integration of remote sensing data with ecological models. 2009/Year 5 Publish study of expansion of Tamarix into Canada. Host specificity testing of Ceutorhynchus assimilis - Data collection, analysis and publication Post-release studies on Diorhabda dispersal, population growth, and impact on target and nontarget plants - Data collection, analysis and publication Impact of C. assimilis on Lepidium fitness parameters - Data collection, analysis and publication Field release experiments using C. assimilis as a biological control agent for Lepidium draba - Data collection Analyze data and
prepare publication on knapweed resistance to Agrobacterium. Complete analysis of herbicide and plant pathogen interaction on white top populations and prepare publication on impact of herbicide and plant pathogen interactions on white top populations. Complete tests of white top pathogens in combination with other plant pathogens to assess synergistic interactions. Continue temporal analysis of regional datasets to evaluate rangeland conditions, trends and risk to weed invasion. Publish study results of rangeland monitoring. Begin functional runs of model/remote sensing data combinations to evaluate actual shifts in rangeland condition and identify causal factors. 4a List the single most significant research accomplishment during FY 2006. Determined reproductive strategy of a biological control target weed: Hoary cress (Lepidium draba) is a perennial herbaceous weed that has invaded agricultural and natural areas of western North America. Invasions are often composed of dense
patches, and it was unclear whether clonal growth via lateral rhizomes or seedling recruitment is the dominant method of patch expansion. To study the clonal structure of this invasive, six patches from three USA populations were analyzed using DNA methods. Results indicated that hoary cress exhibits a strong bias toward patch size increase from clonal reproduction rather than from seedling recruitment. Results indicate that biological control methods that focus on reducing or eliminating seed production would do little to stop expansion of a patch. This accomplishment falls under NP 304 Component 7 Problem Area D: Reproductive Biology and Seed Bank Dynamics. 4b List other significant research accomplishment(s), if any. The isolation of a foreign isolate of Agrobacterium tumefaciens from Euphorbia esula for use as a model biogeographic system to study invasive plant ecology. Sites first surveyed in 1992 surveys where symptoms of crown gall on Euphorbia esula were seen were searched in
2004 and 2005 and the causal organisms isolated. Pathogenicity of the isolates were confirmed, thus essentially providing a set of organisms (accompanying previously described domestic isolates of A. tumefaciens from leafy spurge) with optimal features for addressing a major question in invasive species ecology: whether in the process of migrating from Eurasia to North America, invasives would tend to lose resistance to the agents they are released from. This accomplishment falls under NP 304 Component 7 Problem Area F: Population Dynamics. The extension of a pattern detection of a complex of soilborne plant pathogens (Fusarium and Rhizoctonia spp. and pythiaceous fungi) occurring in conjunction with root galling and damage caused by the root galling Ceutorhynchus spp. weevils throughout sites surveyed in Europe, from Hungary to France. This finding strengthens the need for including the capacity of this weevil to rapidly stimulate negative feedback, through higher disease occurrence
in response to insect root damage, in prerelease studies of potential impact, in line with the emerging consensus that agents should receive such an assessment prior to release. This accomplishment falls under NP 304 Component 9 Problem Area A: Agent Discovery and Selection and Risk Assessment. 5. Describe the major accomplishments to date and their predicted or actual impact. This is the second year of this project and several major accomplishments have already been realized. Diorhabda elongata has been shown to be a complex of 5 well-defined biological species. The genetic analyses we conducted are in strong agreement with collaborators studies on morphological variability and reproductive compatibility. Recognition of these cryptic species provides a basis for more informed evaluation and targeting of the specific Eurasian populations of Diorhabda that should be introduced to North America. This accomplishment falls under NP 304 Component 9 Problem Area C: Field Evaluation.
Molecular evidence for a novel hybrid of invasive Tamarix species has also been discovered. DNA markers were developed and used to identify previously undescribed hybrids of two noxious weed species. Hybrids can potentially exhibit traits that are even more invasive than parental species. The result of this research is inclusion of this hybrid in ongoing biological control investigations, and heightened scrutiny and control of populations in natural areas such as National Parks. This accomplishment falls under NP 304 Component 9 Problem Area B: Field Evaluation. A strong correlation was found between damage caused by root galling weevils (Ceutorhynchus spp.) on white top and the presence of the root- infecting pathogen Rhizoctonia solani. This pathogen is typically undetectable in natural soils. White top plants affected by these insect/plant pathogen interactions are stunted and chlorotic. This is strong evidence that, as has been found with leafy spurge and knapweeds, an efficient
insect/plant pathogen synergism may be the key to efficacious biological control. This accomplishment falls under NP 304 Component 9 Problem Area D: Combining Biological Control Agents. Preliminary tests of differential susceptibility of Russian spotted and diffuse knapweed to the plant cancer causing crown gall bacterium has shown wide differences among populations. These populations include unique haplotypes, differing ploidy levels, putative hybrids, and represent wide geographic origins. Reactions ranged from complete mortality to near immunity to crown gall disease. This accomplishment falls under NP 304 Component 9 Problem Area A: Agent Discovery and Selection and Risk Assessment. Analysis of hyperspectral data in the complex domain accounts for and removes many of the erroneous differences between the images and ground data. Analysis of crop field data collected by yield monitors has resulted in an improvement in predictability from r = 0.368 to r = 0.967. In addition, the data
provide insight into sources of error and how the errors can be reduced. While this data was collected over cropland, much of what was developed can be used in increase our understanding of rangeland conditions and trends. This accomplishment falls under NP 304 Component 7 Problem Area C: Early Detection, Rapid Response and Monitoring. 6. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? The biological and ecological knowledge generated through this project has been made available to other researchers, to land managers and to the public through brochures, field days, scientific meetings and formal publications. For example, we provided over 100,000 saltcedar leaf beetles to federal, state and private cooperators in Montana and Wyoming to start saltcedar
biological control insectaries. We also distributed over 200 brochures entitled Saltcedar Biological Control Program to end- users in Montana, Wyoming and Utah, and started 4 new ARS-managed saltcedar biological control research and insectary sites in Montana. Personnel with the Colorado Dept. of Agriculture visited NPARL to learn and discuss methods for isolating, assessing and utilizing soilborne plant pathogens associated with insect damage to leafy spurge to supplement insect release sites for improved impact. Specialized methods and protocols for sample collection, isolating, identifying, pathogenicity testing, mass culturing and formulating soilborne fungi were explained. 7. List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: List your peer reviewed publications below). Caesar, A.J. Soilborne fungi associated with root galls of Lepidium draba caused by Ceutorhynchus spp. WSSA Annual meeting,
NY, NY Feb 12, 2006 (Abstract). Caesar, A. J. 2006. Rhizosphere bacterial communities associated with insect root herbivory of an invasive plant, Euphorbia esula/virgata. International Society of Microbial Ecology, Vienna Austria, August 18, 2006 (Abstract). Friedman, J., J. Roelle, J. Gaskin and J. Roth. Inherited Latitudinal Variation in Cold Hardiness in Native Populus and Introduced Tamarix. Evolution 2006, Stony Brook, NY June 2006. Gaskin, J., D. Kazmer and P. Shafroth. Novel hybrids produced since the introduction of saltcedar and the influence of garden plantings on nearby invasions. Botanical Society of America 2006, Chico, CA August 2006. Gaskin, J. Hybridization in plant invasions: saltcedar and other examples. 53rd Annual meeting of the Entomological Society of America, Ft. Lauderdale, FL December 2005. Gaskin, J. Genetic studies applied toward the control of plant invasions: from family to population level. University of Idaho CRISSP Series, Moscow, ID October 2005. Holtz
, B.A., McKenry, M.V., Caesar-TonThat, T.C. and Caesar, A. J. 2005. Wood chipping almond brush to reduce air pollution and to study the effect of wood chips on harvest, soil nutrients, soil aggregation, and the microbial community. Almond Board of California, 33rd Almond Industry Conference Proceedings, pages 225-234. Technical Report. Holtz, B., Caesar-TonThat, T.C., Caesar, A. and Hoffman, E.NB2006. The effect of tillage on decomposing mulch, Verticillium, the microbial community, soil nutrients, and soil aggregation. California Pistachio Industry Annual Report Crop Year 2005-2006, page. 103. Holtz, B., Caesar-TonThat, T.C., Caesar, A., and Hoffman, E. The effect of tillage on decomposing mulch, Verticillium, the microbial community, soil nutrients, and soil aggregation. California Pistachio Commission 2005 Production Research Reports, Pages 91-95. Natale, E., S. Zalba and J. Gaskin. Distribution and status of tamarisk (Tamarix spp.) in Argentinean natural environments. XXX Jornadas
Argentinas de Botanica. Santa Fe, Argentina November 2005. Mayer, M., D. Kazmer and J. Gaskin. State of the River. Lower Missouri River Coordinated Resource Management Council. Ft. Peck, MT January 2006. Mayer, M., D.J. Kazmer and J. Gaskin. Biological control and genetics of saltcedar. Big Horn Drainage Exotic Plant Steering Committee Biological Control Seminar. Riverton, WY. October 2005. Kazmer, D.J. and M. Mayer. Biological control of saltcedar. Montana Federal Interagency Noxious Weed Working Group. Billings, MT. March 2006. Mayer, M. and D.J. Kazmer. Biology and biocontrol of saltcedar. Lower Missouri River Coordinated Resource Management Council Annual Meeting. Ft. Peck, MT. January 2006. Mayer, M. and D.J. Kazmer. Biocontrol of saltcedar. Noxious Weed Management Short Course. Sponsored by Western Society of Weed Science. Chico, MT. April 2006.
Impacts
(N/A)
Publications
- Dudley, T.L., Kazmer, D.J. 2005. Field assessment of the risk posed by diorhabda elongata, a biocontrol agent for control of saltcedar (Tamarix spp.), to a non-target plant, frankenia salina. Biological Control. 35:265- 275.
- Gaskin, J.F., Ryan, F.J., Hrusa, G.F. 2006. Genotype diversity of salsola tragus and potential origins of a previously unidentified invasive salsola from california and arizona. Madrono. 53:246-253.
- Gaskin, J.F. 2006. Clonal structure of invasive hoary cress (lepidium draba) infestations. Weed Science. 54(3):428-434.
- Gaskin, J.F. and P.E. Berry. 2005. Smilacaceae in Flora of the Venezuelan Guayana, J.A.Steyermark, P.E. Berry, K. Yatskievych and B.K. Holst (eds.). Missouri Botanical Garden Press, St. Louis, USA. P. 184-193.
- Kremer, R.J., Caesar, A.J., Souissi, T. 2006. Soilborne microorganisms of euphorbia are potential biological control agents of the invasive weed leafy spurge. Applied Soil Ecology. 32(1):27-37.
- Ladenburger, C.G., Hild, A.L., Kazmer, D.J., Munn, L.C. 2005. Soil salinity patterns in Tamarix invasions in the Bighorn Basin, Wyoming, USA. Journal of Arid Environments. 65(2006):111128.
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