Leafy Spurge Control Research Articles

Choosing Species to Enhance Native Plant Abundance Following Biological Control of Leafy Spurge (Euphorbia esula)

Choosing Species to Enhance Native Plant Abundance Following Biological Control of Leafy Spurge (Euphorbia esula)

Foliar Application of Glyphosate Affects Molecular Mechanisms in Underground Adventitious Buds of Leafy Spurge (Euphorbia esula) and Alters Their Vegetative Growth Patterns

Long-term control of leafy spurge with glyphosate requires multiple applications because the plant reproduces vegetatively from abundant underground adventitious buds, referred to as crown and root buds. Determining the molecular mechanisms involved in controlling vegetative reproduction in leafy spurge following foliar glyphosate treatment could identify limiting factors or new targets for manipulation of plant growth and development in invasive perennial species. Thus, we treated leafy spurge plants with 0 or 2.24 kg ai ha−1glyphosate to determine its impact on selected molecular processes in crown buds derived from intact plants and plants decapitated at the soil surface 7 d after glyphosate treatment. New shoot growth from crown buds of foliar glyphosate-treated plants was significantly reduced compared with controls after growth-inducing decapitation, and had a stunted or bushy phenotype. Quantification of a selected set of transcripts involved in hormone biosynthesis and signaling pathways indicated that glyphosate had the most significant impact on abundance ofENT-COPALYL DIPHOSPHATE SYNTHETASE 1, which is involved in a committed step for gibberellin biosynthesis, and auxin transporters includingPINs, PIN-LIKES, andABC TRANSPORTERS. Foliar glyphosate treatment also reduced the abundance of transcripts involved in cell cycle processes, which would be consistent with altered growth patterns observed in this study. Overall, these results suggest that interplay among phytohormones such as auxin, ethylene, and gibberellins affect vegetative growth patterns from crown buds of leafy spurge in response to foliar glyphosate treatment.

Leafy Spurge (Euphorbia esula) Affects Vegetation More Than Seed Banks in Mixed-Grass Prairies of the Northern Great Plains

AbstractExotic plants have the ability to modify soil seed banks in habitats they invade, but little is known about the legacy of invasion on seed banks once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following its removal: a return of native plants, or a secondary invasion of other exotic plants. It is unknown, however, if this difference in plant communities following leafy spurge control is due to seed bank differences. To answer this question, we monitored seed banks and standing vegetation for 2 yr in mixed-grass prairies that were previously invaded by leafy spurge but controlled within 5 yr of our study. We found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community, and leafy spurge invasion history had a larger impact on cover and diversity of the vegetation than on the seed banks. Differences in plant communities following leafy spurge control do not appear to be related to the seed banks, and soil conditions may be more important in determining trajectories of these postinvasion communities.

Phytotoxicity assessment for potential biological control of leafy spurge by soilborne microorganisms

Leafy spurge (Euphorbia esula-virgata), a native of Eurasia, is a serious invasive weed of western grasslands of North America. It is very difficult and cost-prohibitive to control with herbicides; control by insect biological control agents and cultural practices are minimally effective in suppressing vegetative growth and seed production. Current biological control of leafy spurge with pathogens is primarily with mycoherbicides, which require specific environmental conditions and repeated applications to be effective. Alternative biological control approaches using selected microorganisms to attack roots and adventitious shoots may effectively decrease vigor of leafy spurge without environmental manipulations to ensure control efficacy. Our objectives were to survey leafy spurge accessions and their native soils for associated microorganisms, and to assess these microorganisms for potential biological control. A proposed screening protocol, consisting of primary and secondary assays, effectively detected bacteria and fungi with high phytotoxicity toward leafy spurge. Primary lettuce seedling bioassays indicated that 62 % of rhizosphere and 54 % of endorhizal bacteria significantly (P = 0.05) inhibited root growth, causing necrotic lesions. Over 60 % of fungal isolates bioassayed on rice agar significantly inhibited root growth of lettuce seedlings. The most effective microbial isolates, based on primary bioassays, were screened directly on leafy spurge cuttings in secondary assays. Only intact cells of bacteria were detrimental to leafy spurge, indicating that host-bacterial contact was required for pathogenicity. Culture filtrates of 40 % of the test fungi caused complete chlorosis and leaf wilting. The most effective fungi originated from leafy spurge adventitious shoots. Results of the survey suggest that leafy spurge rhizospheres and adventitious shoots are potential sources of biological control microorganisms, which should be considered for inclusion in comprehensive management programs for leafy spurge.

Lack of Native Vegetation Recovery Following Biological Control of Leafy Spurge

Abstract Leafy spurge (Euphorbia esula L.) is an aggressive exotic species that has been successfully suppressed in a variety of situations using classical biological control (flea beetles; Aphthona spp.). This 9-yr study investigated patterns of vegetation responses following significant reductions in leafy spurge cover and density by flea beetles in southeastern Montana. We hypothesized that the vegetation following leafy spurge suppression would be dominated by species and plant functional groups able to persist through heavy infestations. Flea beetles were first released in 1998, and by 2006 leafy spurge foliar cover was reduced 80% to 90% compared to 1998 values on both release and nonrelease plots. Although total cover of the resident vegetation, excluding leafy spurge, increased 72% to 88%, relative cover of the functional groups (native forbs, native sedges, native grasses, and non-native species) was similar among years and between release and nonrelease plots. Mean diversity and mean species ric...

Control of one invasive plant species allows exotic grasses to become dominant in northern Great Plains grasslands

Decline of leafy spurge ( Euphorbia esula) in the northern Great Plains of the US is generally viewed as a success story for biological control, but quality of the vegetation that survived the infestation is key to recovery of ecosystem function. In addition, effects of other invasive species, notably cool-season exotic grasses, must be taken into account. Objectives of this study were (1) to evaluate direction and significance of changes in biomass of native and exotic grasses, forbs, and leafy spurge and in plant species composition following control of leafy spurge by flea beetles and (2) to evaluate the relative effects of leafy spurge and exotic grasses on biomass of native grasses, biomass of forbs, and richness of native species. We monitored species composition (1998–2003 and 2008) and biomass (2000, 2002, 2003 and 2008) of these groups on spurge-infested and noninfested permanent plots at three sites with unbroken prairie sod in North Dakota, USA. We found little evidence, in terms of species richness or biomass of native grasses or forbs, that leafy spurge was being replaced by desirable native species, although desirable as well as weedy and exotic species were characteristic of 2008 vegetation at all three sites. Structural equation models revealed that leafy spurge had temporally intermittent negative effects on forb biomass and species richness, but no effects on native grasses. In contrast, exotic grass had consistently strong, negative effects on native grass biomass, as well as stronger negative effects than leafy spurge on native species richness. Although substantial native plant diversity remains at these sites, exotic grasses pose an important threat to these crucial building blocks of native prairie ecosystems.

Inundative Release of <I>Aphthona</I> spp. Flea Beetles (Coleoptera: Chrysomelidae) as a Biological “Herbicide” on Leafy Spurge in Riparian Areas

Inundative releases of beneficial insects are frequently used to suppress pest insects but not commonly attempted as a method of weed biological control because of the difficulty in obtaining the required large numbers of insects. The successful establishment of a flea beetle complex, mixed Aphthona lacertosa (Rosenhauer) and Aphthona nigriscutus Foundras (87 and 13%, respectively), for the control of leafy spurge, Euphorbia esula L., provided an easily collectable source of these natural enemies that enabled us to attempt inundative release as a possible leafy spurge control method in a sensitive riparian ecological zone where chemical control is restricted. Our target weed populations were small isolated patches of leafy spurge along three streams in southwestern, central, and northeastern Idaho. This study assessed leafy spurge and associated vegetation responses to inundative releases of 10 and 50 beetles per spurge flowering stem over two consecutive years. Releasing 10 beetles per flowering stem had inconclusive effects on spurge biomass, crown, stem, and seedling density. Alternatively, releasing 50 beetles per flowering stem resulted in a reduction of biomass, crown and stem density in the range of 60-80% at all three study sites, and about an approximately 60% reduction of seedling density at one site, compared with untreated plots. In contrast to leafy spurge, associated vegetation did not conclusively respond to beetle release, indicating that it may take more than two years for desired riparian vegetation to respond to reductions in leafy spurge competition.

Integrated Leafy Spurge (Euphorbia esula) Control Using Imazapic, Aphthona spp. Biological Control Agents, and Seeded Native Grasses

Abstract Chemical, cultural, and biological methods have been developed to control leafy spurge in a variety of environments. Aphthona spp. biological control agents have established throughout the northern Great Plains and Rocky Mountain region and successfully controlled leafy spurge in many areas, but notable exceptions include areas with sandy soils. Leafy spurge control can be improved by combining methods such as chemical, biological, or cultural treatments, compared to a single method used alone. The effects of Aphthona spp., imazapic herbicide, and interseeded native grass species alone or in combination for leafy spurge control were evaluated at two locations in southeastern North Dakota for 5 yr. Both the Sheyenne National Grassland (SNG) and Walcott, ND, study locations had greater than 80% sand soil. Leafy spurge stem density, canopy cover, and yield were reduced for 1 to 2 yr in all treatments that included imazapic, with no difference in control between single and combination treatments. Aph...

Leafy Spurge Suppression by Flea Beetles in The Little Missouri Drainage Basin, USA

The Ecological Area-wide Management Leafy Spurge , or TEAM Leafy Spurge, began collecting and redistributing flea beetles ( Aphthona spp.) to research/demonstration sites and landowners throughout the Little Missouri River drainage basin to control leafy spurge in 1998. A study to evaluate the change over time of leafy spurge ( Euphorbia esula L.) phytosociological characteristics following release of flea beetles was initiated in 2002 on leafy spurge–infested pasture and rangeland in the Little Missouri River drainage of Montana, North Dakota, South Dakota, and Wyoming. A total of 292 flea beetle release sites were analyzed in June and July 2002 and 2003 for leafy spurge stem density, foliar cover, flea beetle density, and vegetation composition. Leafy spurge stem density suppression was evident at 91% of the study sites. On two-thirds of the study sites stem density was reduced from greater than 100 stems·m −1 to less than 25 stems·m −1 . Leafy spurge foliar cover was less than 5% on approximately two-thirds of the flea beetle release sites and less than 25% on over 90% of the release sites. Area of observed leafy spurge suppression ranged from 0 m 2 to 30000 m 2 . Approximately 40% of the release sites had leafy spurge suppression ranging from 1000 m 2 to 5000 m 2 , and 14% of the release sites had greater than 10000 m 2 of leafy spurge control. Plant community composition following leafy spurge suppression was characteristic of native plant communities that had not been burned or grazed. Flea beetles effectively reduced leafy spurge stem density and cover in 4–5 yr across a variety of locations and corresponding environmental conditions, both within the Little Missouri River drainage and in selected nearby locations. Para llevar a cabo el Manejo Ecológico de una amplia área de euphorbia fondosa se comenzó a recoger y a redistribuir escarabajos de pulga ( Aphthona spp.) con la finalidad tanto de investigar y/o demostrarle a los propietarios localizados en sitios a lo largo de la cuenca del rio Little Missouri como controlar la euphorbia frondosa en 1998. Se llevo a cabo primero un estudio para evaluar el cambio de las características fitosociologías de la euphorbia ( Euforbio esula L.) seguido después de la liberación de escarabajos de pulga en 2002 en un pastizal infestado de euphorbia en la cuenca del río Little Missouri en Montana, Dakota del Norte, Dakota del Sur y Wyoming. En un total de 292 sitios donde fueron liberados escarabajos de pulga fueron analizados en cuanto a la densidad de tallos de euphorbia, cubertura foliar, densidad de escarabajos de pulga y composición de la vegetación en Junio y Julio 2002 y 2003. La supresión de tallos de euphorbia fue evidente en el 91% de los sitios en estudio. En dos tercios de los sitios la densidad de tallos fue reducida de más de 100 tallos m 2 a menos de 25 tallos m 2 . La cubierta foliar fue menos de 5% en aproximadamente dos tercios de los sitios de liberación de escarabajos de pulga y menos de 25% en 90% de los sitios de de liberación. El área de supresión de euphorbia frondosa fue 0 m 2 a 30000 m 2 . Aproximadamente 40% de los sitios de liberación que tuvieron supresión de euphorbia frondosa se extendieron de 1000 m 2 a 5000 m 2 y el 14% de los sitios de liberación tuvieron mayor de 10000 m 2 de control de euphorbia. La composición de la comunidad de plantas después de la supresión de la euphorbia fue característica de comunidades de plantas nativas que no habían sido quemadas o pastoreadas. Los escarabajos de la pulga redujeron con eficiencia la densidad y cubertura de tallos de euphorbia a través de una variedad de localidades y condiciones ambientales dentro de la cuenca del río Little Missouri y áreas adyacentes.

Leafy Spurge (Euphorbia esula) Control with Aphthona spp. Affects Seedbank Composition and Native Grass Reestablishment

Aphthona spp. flea beetles have established and reduced the density of leafy spurge in much of the western United States. One way to measure the long-term impact and effectiveness of a weed control program is by monitoring the changes in the seedbank over time. The change in leafy spurge stem density and seed in the seedbank were evaluated 5 yr after Aphthona spp. were released to control this weed in the Little Missouri National Grasslands in southwestern North Dakota. Leafy spurge density and seed in both loamy overflow and loamy ecological sites decreased, whereas desirable (high-seral) forbs increased 5 yr after the biological control agents were released. Leafy spurge topgrowth was reduced from an average of over 200 stems/m2 to less than 8 stems/m2 in the most densely infested sites, and leafy spurge seed was reduced from an average of 68% of the seedbank to only 14% in both ecological sites. High-seral forb seed increased by over 300% in the seedbank, which indicated the floristic quality of the sites, was returning to a preinfestation state. Species with the largest increase included western rock jasmine and fringed sage, which increased at least three-fold in both sites. Less desirable low-seral forbs and grasses accounted for about 30% of the seedbank. In a greenhouse study, native grass production was reduced nearly 50% when grown in soil from Aphthona spp. release sites compared to nonrelease sites. Switchgrass production was reduced to a greater extent (66%) than green needlegrass, little bluestem, or western wheatgrass. The cause and extent of reduced native grass production in sites where Aphthona spp. were released has yet to be determined. The decrease in leafy spurge topgrowth and seed in the soil seedbank as desirable species seed increased, should lead to the long-term recovery of the plant community.Nomenclature: Leafy spurge, Euphorbia esula L. EPHES; fringed sage, Artemisia frigida Willd; green needlegrass, Nassella viridula (Trin.) Barkworth; little bluestem, Schizachyrium scoparium (Michx.) Nash-Gould; switchgrass, Panicum virgatum L.; western rock jasmine, Androsace occidentalis Pursh; western wheatgrass, Pascopyrum smithii (Rydb.) A. Löve.

Seasonal Photosynthesis and Partitioning of Nonstructural Carbohydrates in Leafy Spurge (Euphorbia esula)

Previous evidence indicates that changes in well-defined phases of dormancy in underground adventitious buds of leafy spurge in late summer and autumn are regulated by complex sensing and signaling pathways involving aboveground sugar signals. However, little information exists concerning seasonal photosynthesis and carbohydrate partitioning of leafy spurge, although such information would help to elucidate the involvement of sugar in controlling bud dormancy. An outdoor study was conducted over two growing seasons to determine and model seasonal patterns of photosynthesis and aboveground carbohydrate partitioning and their relationship to underground adventitious bud carbohydrate status. Photosynthesis and total nonstructural carbohydrate (TNC) content of aboveground tissues was greatest during vegetative growth. Photosynthesis gradually declined over the growing season, whereas TNC decreased sharply during flowering, followed by a gradual decline between midsummer and autumn. Leaf starch increased dramatically to midsummer before declining sharply throughout late summer and early autumn, whereas sucrose content responded inversely, indicating a mobilization of starch reserves and export of sugars to overwintering belowground sink tissues. Because newly formed underground adventitious buds showed a continuous increase in TNC from midsummer through autumn, export of sugars from aboveground tissues likely contributed to the increase in TNC. These results may facilitate new strategies for biological control of leafy spurge.

Effect of matrix habitat on the spread of flea beetle introductions for biological control of leafy spurge

Matrix habitats are known to influence the movement patterns of a variety of species but it is less well known whether these effects have strong implications for spatial population dynamics, including the spread of biological introductions. Using a spatially explicit simulation model parameterized with empirical data, we examine how grass and shrub matrix habitats, each offering different resistance to dispersal, influence the spread and impact of a biocontrol agent, Aphthona lacertosa, on the invasive weed, leafy spurge. Model predictions indicate that differential responses to matrix habitat have little effect on the agent’s spread over the study landscape and this is supported by statistical models fit to observed A. lacertosa incidence on the same landscape. Subsequent experimentation with the simulation model suggested that A. lacertosa colonization rates were largely unaffected by increases in amount of the more restrictive shrub matrix. However, simulations of an hypothetical species with greater overall dispersal ability but reduced dispersal rate through shrub matrix showed that colonization rates were noticeably reduced when the percentage of shrub matrix on the landscape approached 50%. Combined these results suggest that some tailoring of release strategies may be required to accommodate the unique dispersal capabilities of different biocontrol agents on particular release landscapes, but for A. lacertosa there appears to be little effect of matrix habitat structure on rates of spread.

Efficacy of Flea Beetle Control of Leafy Spurge in Montana and South Dakota

Black (Aphthona lacertosa and Aphthona czwalinae) and brown (Aphthona nigriscutis) flea beetles are among the more successful biological control agents used in the control and management of leafy spurge on a relatively large scale in the Northern Great Plains. The objectives of this study were to document leafy spurge population dynamics in response to control by black and brown flea beetles, determine the role of selected site characteristics on establishment and persistence of the beetles, and evaluate the general response of the resident vegetation to control of leafy spurge. In late June 1998, about 3 000 insects of each species were released into permanently marked plots in northwestern South Dakota and southeastern Montana. Beetle abundance, density and foliar cover of leafy spurge, and foliar cover of the resident vegetation were evaluated each year from 1998 through 2004. Black beetles increased rapidly and peaked at 65% of their measurable potential abundance within 2 years (P < 0.05) following release and dominated all release plots throughout the study. Although population growth characteristics of black flea beetles were highly variable, the successful patterns in reducing the dominance of leafy spurge were fairly consistent. By 2004, foliar cover of leafy spurge on both release and nonrelease plots was significantly reduced compared to prerelease values. Foliar cover of grass and grasslike plants increased concomitantly with the reduction in leafy spurge dominance while cover of forbs on release and nonrelease plots remained consistently below noninfested values.

Biological Control of Leafy Spurge: Utilization and Implementation

Leafy spurge is an exotic, noxious, perennial weed which is widely established in the north central United States and is an especially serious problem in the northern Great Plains. In 1997, the Agricultural Research Service and Animal and Plant Health Inspection Service, US Department of Agriculture, initiated a major Integrated Pest Management (IPM) research and demonstration project, The Ecological Area-wide Management (TEAM) Leafy Spurge (TLS), to develop and demonstrate ecologically based IPM strategies that can produce effective, affordable leafy spurge control. A key component of the TLS project was expanding the use of biological control agents. To assess the level of insect utilization and implementation and the level of current and perceived future control of leafy spurge as a result of biological control agents, a mail survey of 468 individuals that obtained biological control agents (insects) at TLS-sponsored events and of all the county weed boards in North Dakota, South Dakota, Montana, and Wyoming was conducted. Forty-six percent of the landowner/land managers and 70% of the county weed boards responded to the questionnaire. Respondents reported basic information about the number and characteristics of release sites, and characteristics of the leafy spurge stands, as well as the level of control to date and perceived level of eventual control.

Evaluation of TEAM Leafy Spurge Project

Leafy spurge (Euphorbia esula L.) is an exotic, noxious, perennial weed which is widely established in the north central United States and is an especially serious problem in the northern Great Plains. In 1997, the Agricultural Research Service and Animal and Plant Health Inspection Service, U.S. Department of Agriculture, initiated a major Integrated Pest Management (IPM) research and demonstration project to develop and demonstrate ecologically based IPM strategies that can produce effective, affordable leafy spurge control. In 1998 and 1999, a survey of ranchers, local decision makers, and public land managers was conducted to evaluate managerial, institutional, and social factors that might affect the rate and extent of implementation of various control strategies. In 2001, a second survey of the same ranchers, local decision makers, and public land managers was conducted to 1) assess any changes in land managers’ perceptions of weed problems, control alternatives, and related issues and 2) evaluate the impact of The Ecological Area-wide Management (TEAM) Leafy Spurge (TLS) project on the respondents’ weed control practices. Findings from the first survey identified a number of constraints limiting land managers’ ability to utilize available control techniques to manage leafy spurge infestations. The TLS project used a variety of tools and communication strategies, such as presentations at local meetings, demonstration plots, and field days, to communicate and demonstrate weed control strategies and address the impediments to leafy spurge control identified in the first survey. Findings from the second survey indicated TLS efforts had effectively addressed many of the constraints to leafy spurge control previously reported by landowners and land managers.

Effect of Herbicides for Leafy Spurge Control on the Western Prairie Fringed Orchid

Abstract Leafy spurge has invaded the habitat of the western prairie fringed orchid, a federally listed threatened species. Imazapic ([±]-2-[4,5-dihydro-4-methyl-4-{1-methylethyl}-5-oxo-1 H -imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid) and quinclorac (3,7-dichloroquinoline-8-carboxylic acid) are relatively new herbicides that control leafy spurge and can be used in the mesic areas where the orchid is found. Research was initiated to evaluate the effects of imazapic and quinclorac on the survival and fecundity of the western prairie fringed orchid. Herbicides were applied at the commonly used and maximum labeled rates in mid-September. This timing is optimum for leafy spurge control with quinclorac and imazapic and the orchid generally has senesced by mid-September, making injury less likely. Quinclorac applied at 840 and 1 120 g·ha −1 did not affect regrowth or fecundity of the western prairie fringed orchid 1 or 2 years after treatment. Orchids treated with quinclorac at 840 or 1 120 g·ha −1 generally were as tall, had racemes as long as, and produced as many flowers and seed capsules as untreated orchids. In contrast, orchids treated with imazapic at 140 or 210 g·ha −1 tended to regrow as vegetative plants and were shorter, had shorter racemes, and produced fewer flowers and seed capsules than untreated orchids. Orchids treated with imazapic averaged 21 cm in height and produced an average of 1 flower per plant 10 months after treatment, whereas untreated orchids and orchids treated with quinclorac were approximately 36 cm in height and produced 5 flowers per plant. Quinclorac could be a valuable tool to control leafy spurge in the habitat of the orchid because orchids treated with quinclorac regrew as vigorously and were as fecund as untreated orchids. However, the current quinclorac label prohibits grazing or haying for 309 days after application.

Phenology of first and peak emergence of Aphthona lacertosa and A. nigriscutis: Two flea beetles introduced for biological control of leafy spurge, Euphorbia esula L.

Nonlinear models were used to estimate first emergence and peak abundance dates for Aphthona lacertosa Rosenhauer and A. nigriscutis Foudras, two flea beetles introduced to control leafy spurge, Euphorbia esula L., in North America. For model development, 26 field sites were sampled for flea beetle abundance at weekly intervals for eight weeks in three western Minnesota counties in 2000, 2001, and 2002. A three-parameter Weibull function, fit to observed cumulative probability distributions, were used to predict accumulated degree-days (ADD) to first emergence. Bias testing indicated the Weibull function provided a useful estimate of first emergence for A. lacertosa (304 ADD, lower developmental threshold 7.5 °C), but failed to produce a useful estimate for A. nigriscutis. A third-order polynomial was used to approximate seasonal abundance and predict peak abundance for each species. Estimated ADD to peak abundance of A. lacertosa was 594 ± 24 (DD > 7.5 °C) and 670 ± 15 (DD > 9.3 °C) for A. nigriscutis. Models were validated with additional data sets from Minnesota, Montana, and North Dakota. Estimated date of peak emergence provided useful predictions of peak emergence for Minnesota and North Dakota, but failed to predict peak emergence in Montana. We speculate that variation in climate and environmental conditions between Midwestern states and Montana were responsible for differing emergence patterns. We conclude that phenology models should be developed regionally to provide useful predictions of peak emergence for land managers. Maps were developed for Minnesota to spatially display predicted dates of peak abundance for A. lacertosa and A. nigriscutis.

Efficacy of Flea Beetle Control of Leafy Spurge in Montana and South Dakota

Black (Aphthona lacertosa and Aphthona czwalinae) and brown (Aphthona nigriscutis) flea beetles are among the more successful biological control agents used in the control and management of leafy spurge on a relatively large scale in the Northern Great Plains. The objectives of this study were to document leafy spurge population dynamics in response to control by black and brown flea beetles, determine the role of selected site characteristics on establishment and persistence of the beetles, and evaluate the general response of the resident vegetation to control of leafy spurge. In late June 1998, about 3 000 insects of each species were released into permanently marked plots in northwestern South Dakota and southeastern Montana. Beetle abundance, density and foliar cover of leafy spurge, and foliar cover of the resident vegetation were evaluated each year from 1998 through 2004. Black beetles increased rapidly and peaked at 65% of their measurable potential abundance within 2 years (P &lt; 0.05) following release and dominated all release plots throughout the study. Although population growth characteristics of black flea beetles were highly variable, the successful patterns in reducing the dominance of leafy spurge were fairly consistent. By 2004, foliar cover of leafy spurge on both release and nonrelease plots was significantly reduced compared to prerelease values. Foliar cover of grass and grasslike plants increased concomitantly with the reduction in leafy spurge dominance while cover of forbs on release and nonrelease plots remained consistently below noninfested values.

Biological Control of Leafy Spurge: Utilization and Implementation

Leafy spurge is an exotic, noxious, perennial weed which is widely established in the north central United States and is an especially serious problem in the northern Great Plains. In 1997, the Agricultural Research Service and Animal and Plant Health Inspection Service, US Department of Agriculture, initiated a major Integrated Pest Management (IPM) research and demonstration project, The Ecological Area-wide Management (TEAM) Leafy Spurge (TLS), to develop and demonstrate ecologically based IPM strategies that can produce effective, affordable leafy spurge control. A key component of the TLS project was expanding the use of biological control agents. To assess the level of insect utilization and implementation and the level of current and perceived future control of leafy spurge as a result of biological control agents, a mail survey of 468 individuals that obtained biological control agents (insects) at TLS-sponsored events and of all the county weed boards in North Dakota, South Dakota, Montana, and Wyoming was conducted. Forty-six percent of the landowner/land managers and 70% of the county weed boards responded to the questionnaire. Respondents reported basic information about the number and characteristics of release sites, and characteristics of the leafy spurge stands, as well as the level of control to date and perceived level of eventual control.

Effect of Herbicides for Leafy Spurge Control on the Western Prairie Fringed Orchid

Leafy spurge has invaded the habitat of the western prairie fringed orchid, a federally listed threatened species. Imazapic ([6]-2- [4,5-dihydro-4-methyl-4-f1-methylethylg-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid) and quinclorac (3,7- dichloroquinoline-8-carboxylic acid) are relatively new herbicides that control leafy spurge and can be used in the mesic areas where the orchid is found. Research was initiated to evaluate the effects of imazapic and quinclorac on the survival and fecundity of the western prairie fringed orchid. Herbicides were applied at the commonly used and maximum labeled rates in mid-September. This timing is optimum for leafy spurge control with quinclorac and imazapic and the orchid generally has senesced by mid-September, making injury less likely. Quinclorac applied at 840 and 1 120 g ha-1 did not affect regrowth or fecundity of the western prairie fringed orchid 1 or 2 years after treatment. Orchids treated with quinclorac at 840 or 1 120 g ha-1 generally were as tall, had racemes as long as, and produced as many flowers and seed capsules as untreated orchids. In contrast, orchids treated with imazapic at 140 or 210 g ha-1 tended to regrow as vegetative plants and were shorter, had shorter racemes, and produced fewer flowers and seed capsules than untreated orchids. Orchids treated with imazapic averaged 21 cm in height and produced an average of 1 flower per plant 10 months after treatment, whereas untreated orchids and orchids treated with quinclorac were approximately 36 cm in height and produced 5 flowers per plant. Quinclorac could be a valuable tool to control leafy spurge in the habitat of the orchid because orchids treated with quinclorac regrew as vigorously and were as fecund as untreated orchids. However, the current quinclorac label prohibits grazing or haying for 309 days after application.