Progress 11/02/15 to 11/01/20
Outputs
Progress Report Objectives (from AD-416): Biological control is considered the only long-term control option for many invasive plants. Enhancing the probability of successful biological control requires the identification of not only host-specific biological control agents (although non-specific agents may be feasible in certain situations) but also effective agents. This in turn depends upon a fundamental knowledge of a target weed⿿s biology, genetics, and population dynamics to inform agent selection. Long-term monitoring is needed to verify the specificity and efficacy of field-released agents. It is also important to understand why biological control may not be feasible with currently available agents. Our objectives are to: Objective 1: Evaluate host specificity, efficacy, or other biological traits of biological control agents of invasive plants, especially swallow-wort and eastern knapweeds; and determine the biology, ecology and demography of these weeds. Subobjective 1a: Assess agents of swallow-wort and knapweed. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Approach (from AD-416): European swallow-worts (Vincetoxicum spp.) and knapweeds (Centaurea spp.) are invasive weeds of continued or increasing concern, respectively, in the northeastern U.S. They invade a variety of natural and managed terrestrial ecosystems. A biological control program for swallow-worts has been in development since 2004. This project will evaluate remaining potential insect and fungal agents of swallow-wort for host range and/or life history traits and plant impact in laboratory, greenhouse and (as appropriate) field studies, and implement a biological control agent (a defoliating moth that is anticipated for approval) to control pale and black swallow-wort. Long-term monitoring plots, already established at several sites, will help document the released agent⿿s impact on swallow- wort and resulting responses of invaded plant communities. A remaining knowledge gap of swallow-wort demography (years to first reproduction) will continue to be investigated in a field experiment. The genetics of the fertile hybrid meadow knapweed and demography of northeastern populations of spotted and meadow knapweed will be investigated through field and common garden studies. Initial assessment of a seed-feeding biological control agent on meadow knapweed will be made in the greenhouse to understand its potential impact. Successful implementation of this program should lead to the suppression of the two swallow-wort species in some of the habitats they have invaded, and define future control measures to be implemented against knapweeds. This is the final report for Project 8062-22620-005-00D which will end by November 1, 2020. A new project entitled ⿿Management and Biology of Arthropod Pests and Arthropod-Borne Plant Pathogens is under OSQR review. Subobjective 1a: Assess agents of swallow-wort and knapweed. The biology and host specificity of four candidate biological control agents of pale and black swallow-wort were assessed over the last five years. In collaboration with Russian and French researchers, it was demonstrated in laboratory and field studies that the leaf-feeding moth Abrostola asclepiadis will only produce one generation per summer if it were to be released into the United States. The ARS researcher also documented that a single defoliation by the larvae has very limited impacts on swallow- worts and insect damage was not enhanced by shading or competition with other plants. The moth A. asclepiadis will therefore be of limited effectiveness in reducing pale and black swallow-wort populations based on previously produced plant models, and it is recommended that this insect be given a low priority for release (two manuscripts published). The seed-destroying fly Euphranta connexa, the second biocontrol agent of swallow-wort, was evaluated for its host specificity by Swiss collaborators. Egg-laying by adult flies into seed pods and successful development of larvae on plant species, besides the normal swallow-wort hosts, was limited to a European species not present in North America. The fly may be suitably host specific but additional testing is required. Testing protocols must still be further refined to ensure high quality seed pods of several plant species are available in large numbers for testing when insects are available. Additional tests have been suspended to focus on a more promising root-feeding beetle. Larvae of the root-feeding beetle Chrysochus asclepiadeus, the third agent, were previously shown in laboratory tests to develop on some North American milkweeds, which are closely related to European swallow-worts. Additional laboratory tests with a French population of the beetle are underway. However, an open-field test by Swiss collaborators showed that adult beetles only fed and laid eggs on swallow-wort plants. Thus, the risk of damage to other plant species appears to be very low under natural field conditions. Follow-up field tests by a French collaborator initiated in 2019, in which beetles only had access to individual species of plants, confirmed that adult beetles did not feed on common milkweed plants although a few larvae were subsequently found on milkweed roots in one of two tests. In contrast, swallow-wort plants were heavily defoliated and had much larger numbers of larvae. Another French open- field test using higher densities of adult beetles is currently in progress. The fungus Sclerotium rolfsii, the fourth agent, was previously discovered killing pale swallow-wort in New York; it was being evaluated as a potential management option for swallow-worts. In collaboration with a plant pathologist, it was shown to be highly virulent to adult flowering plants, similar to previous tests involving seedlings. A two- year overwintering survival study of the pathogen demonstrated that fungal survival by mid-summer was poorer with shallow burial of the fungus compared to fungi on the soil surface. Potential changes in the associated plant community and incidence of disease at the discovery site were documented. The same fungus has recently been documented to cause disease in table beets in New York. Therefore, future studies involving the fungus will need to consider impacts on agricultural crops. A manuscript is in preparation. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Meadow knapweed is widespread in the Northeast and is considered to be a hybrid between black and brown knapweeds (parent species), all of which were introduced from Europe. A manuscript has been published on the population genetics of 10 New York and 10 Vermont populations. Analyses by collaborators at the University of Vermont indicate that three genetic groups are present, extensive mixing among the groups has occurred, and genome size is correlated with genetic ancestry. Additional sampling by collaborators occurred in the Pacific Northwest, where meadow knapweed has long been present, to understand whether this hybrid knapweed resulted from a cross-continental move from Europe or an intracontinental move West to East in the United States. Seeds, leaf and seed head samples were collected from 16 populations distributed across Oregon and Washington. DNA extractions will soon be underway, and morphological measurements of seed heads are planned. In addition, seeds will be used for future common garden experiments comparing quantitative plant traits between western and eastern U.S. populations. Genetic and morphological data will also be compared to European samples collected from six countries. Seeds from the same New York and Vermont populations were germinated and grown in a common greenhouse study by University of Vermont collaborators to correlate various plant and genetic traits with known invasive traits. A second generation experiment was also conducted involving offspring created by selectively crossing parents of different genetic lineages. Plant traits thought to be related to invasiveness showed significant heritability and a strong correlation with the hybrid. A manuscript is in preparation. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. The time to reproductive maturity may be a critical phase in the life cycle of swallow-worts. Data were collected from a long-term field experiment assessing survival and years to flowering of vegetative juveniles of pale and black swallow-wort in different habitats and locations. Individual plants of black swallow-wort began reproducing at a faster rate (beginning at 3-4 years) compared to pale swallow-wort (6-8 years). Many plants, especially pale swallow-wort, took up to 10 years to flower (manuscript in preparation). If swallow-wort biological control is of limited availability, alternative control measures will continue to be needed by land managers. A manuscript was published on a multi-year mowing study of pale swallow- wort. Mowing at least three times within a season prevented seed production beginning the first year but did not reduce pale swallow-wort densities and cover until the fifth year of mowing. Mowing six times per season did not enhance control. Land managers are being advised that they must mow at least three times annually to prevent the production and spread of seeds, and that it will take several years to reduce but not eliminate existing stands of pale swallow-wort. Also, a three-year herbicide trial will be concluded this summer to assess the efficacy of different herbicides in combination with mowing against black swallow- wort. Currently, no data exist on herbicidal control of black swallow- wort. Spotted and meadow knapweed invade a variety of agricultural fields and natural areas, and they are a potentially new and emerging weed problem for the Northeast. Plant population data, including survival of different life stages and seed production, and information on plant phenology were collected over three years from three spotted knapweed and four meadow knapweed field sites in New York. In addition, the presence of biological control agents that were previously released in the region was documented (manuscript in press). A collaborator (University of Vermont) is currently analyzing these data using a plant population modeling approach. Initial results show that six of the seven populations are increasing in size, and that disruption of the seedling and flowering stages may be important for controlling knapweed populations. Knapweed seed bank and seedling emergence studies were established in fall 2018. Data are being collected with a collaborator to determine how many years buried seeds of spotted and meadow knapweed survive and how successfully knapweed seedlings emerge from different burial depths over time. Deeply buried seeds generally did not germinate and had greater than 90% survival after one year. In contrast, most seeds on the soil surface or that were slightly buried germinated within the first year. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Long-term monitoring of vegetation plots occurred prior to release of a biological control agent at several sites in New York State. At some sites, the presence of swallow-wort was correlated with a decline in plant diversity and abundance over time (manuscript in preparation). The biological control agent Hypena opulenta, a moth whose larvae defoliate swallow-worts, was first released in New York State in 2018 at two locations. Two generations per summer were likely based on observations of caged insects. Plant population models developed by us indicated this moth could be an effective agent against slow-growing swallow-wort populations (typically forests), but it may only have a limited impact on faster-growing infestations in fields. Despite some evidence of successful overwintering in spring 2019, the populations of the moth died out during summer 2019. It was simultaneously discovered by ARS scientists at Ithaca that all colonies of the moth in North America were infected with a pathogen. This prevented additional releases in 2019. A new moth colony has been established which is currently being reared for releases this summer.
Impacts
(N/A)
Publications
- Milbrath, L.R., Dolgovskaya, M., Volkovitsh, M., Sforza, R., Biazzo, J. 2020. Photoperiodic response of Abrostola asclepiadis (Lepidoptera: Noctuidae), a candidate biological control agent for swallow-worts (Vincetoxicum, Apocynaceae). Great Lakes Entomologist. 52:71-77.
- Biazzo, J., Milbrath, L.R. 2019. Response of pale swallowwort (Vincetoxicum rossicum) to multiple years of mowing. Invasive Plant Science and Management. 12(3).
- Lachmuth, S., Molofsky, J., Milbrath, L.R., Suda, J., Keller, S.R. 2019. Associations between genomic ancestry, genome size and capitula morphology in the invasive meadow knapweed hybrid complex (Centaurea ÿmoncktonii) in eastern North America. AoBP (Annals of Botany PLANTS). 11(5).
|
Progress 10/01/19 to 09/30/20
Outputs
Progress Report Objectives (from AD-416): Biological control is considered the only long-term control option for many invasive plants. Enhancing the probability of successful biological control requires the identification of not only host-specific biological control agents (although non-specific agents may be feasible in certain situations) but also effective agents. This in turn depends upon a fundamental knowledge of a target weed⿿s biology, genetics, and population dynamics to inform agent selection. Long-term monitoring is needed to verify the specificity and efficacy of field-released agents. It is also important to understand why biological control may not be feasible with currently available agents. Our objectives are to: Objective 1: Evaluate host specificity, efficacy, or other biological traits of biological control agents of invasive plants, especially swallow-wort and eastern knapweeds; and determine the biology, ecology and demography of these weeds. Subobjective 1a: Assess agents of swallow-wort and knapweed. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Approach (from AD-416): European swallow-worts (Vincetoxicum spp.) and knapweeds (Centaurea spp.) are invasive weeds of continued or increasing concern, respectively, in the northeastern U.S. They invade a variety of natural and managed terrestrial ecosystems. A biological control program for swallow-worts has been in development since 2004. This project will evaluate remaining potential insect and fungal agents of swallow-wort for host range and/or life history traits and plant impact in laboratory, greenhouse and (as appropriate) field studies, and implement a biological control agent (a defoliating moth that is anticipated for approval) to control pale and black swallow-wort. Long-term monitoring plots, already established at several sites, will help document the released agent⿿s impact on swallow- wort and resulting responses of invaded plant communities. A remaining knowledge gap of swallow-wort demography (years to first reproduction) will continue to be investigated in a field experiment. The genetics of the fertile hybrid meadow knapweed and demography of northeastern populations of spotted and meadow knapweed will be investigated through field and common garden studies. Initial assessment of a seed-feeding biological control agent on meadow knapweed will be made in the greenhouse to understand its potential impact. Successful implementation of this program should lead to the suppression of the two swallow-wort species in some of the habitats they have invaded, and define future control measures to be implemented against knapweeds. This is the final report for Project 8062-22620-005-00D which will end by November 1, 2020. A new project entitled ⿿Management and Biology of Arthropod Pests and Arthropod-Borne Plant Pathogens is under OSQR review. Subobjective 1a: Assess agents of swallow-wort and knapweed. The biology and host specificity of four candidate biological control agents of pale and black swallow-wort were assessed over the last five years. In collaboration with Russian and French researchers, it was demonstrated in laboratory and field studies that the leaf-feeding moth Abrostola asclepiadis will only produce one generation per summer if it were to be released into the United States. The ARS researcher also documented that a single defoliation by the larvae has very limited impacts on swallow- worts and insect damage was not enhanced by shading or competition with other plants. The moth A. asclepiadis will therefore be of limited effectiveness in reducing pale and black swallow-wort populations based on previously produced plant models, and it is recommended that this insect be given a low priority for release (two manuscripts published). The seed-destroying fly Euphranta connexa, the second biocontrol agent of swallow-wort, was evaluated for its host specificity by Swiss collaborators. Egg-laying by adult flies into seed pods and successful development of larvae on plant species, besides the normal swallow-wort hosts, was limited to a European species not present in North America. The fly may be suitably host specific but additional testing is required. Testing protocols must still be further refined to ensure high quality seed pods of several plant species are available in large numbers for testing when insects are available. Additional tests have been suspended to focus on a more promising root-feeding beetle. Larvae of the root-feeding beetle Chrysochus asclepiadeus, the third agent, were previously shown in laboratory tests to develop on some North American milkweeds, which are closely related to European swallow-worts. Additional laboratory tests with a French population of the beetle are underway. However, an open-field test by Swiss collaborators showed that adult beetles only fed and laid eggs on swallow-wort plants. Thus, the risk of damage to other plant species appears to be very low under natural field conditions. Follow-up field tests by a French collaborator initiated in 2019, in which beetles only had access to individual species of plants, confirmed that adult beetles did not feed on common milkweed plants although a few larvae were subsequently found on milkweed roots in one of two tests. In contrast, swallow-wort plants were heavily defoliated and had much larger numbers of larvae. Another French open- field test using higher densities of adult beetles is currently in progress. The fungus Sclerotium rolfsii, the fourth agent, was previously discovered killing pale swallow-wort in New York; it was being evaluated as a potential management option for swallow-worts. In collaboration with a plant pathologist, it was shown to be highly virulent to adult flowering plants, similar to previous tests involving seedlings. A two- year overwintering survival study of the pathogen demonstrated that fungal survival by mid-summer was poorer with shallow burial of the fungus compared to fungi on the soil surface. Potential changes in the associated plant community and incidence of disease at the discovery site were documented. The same fungus has recently been documented to cause disease in table beets in New York. Therefore, future studies involving the fungus will need to consider impacts on agricultural crops. A manuscript is in preparation. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Meadow knapweed is widespread in the Northeast and is considered to be a hybrid between black and brown knapweeds (parent species), all of which were introduced from Europe. A manuscript has been published on the population genetics of 10 New York and 10 Vermont populations. Analyses by collaborators at the University of Vermont indicate that three genetic groups are present, extensive mixing among the groups has occurred, and genome size is correlated with genetic ancestry. Additional sampling by collaborators occurred in the Pacific Northwest, where meadow knapweed has long been present, to understand whether this hybrid knapweed resulted from a cross-continental move from Europe or an intracontinental move West to East in the United States. Seeds, leaf and seed head samples were collected from 16 populations distributed across Oregon and Washington. DNA extractions will soon be underway, and morphological measurements of seed heads are planned. In addition, seeds will be used for future common garden experiments comparing quantitative plant traits between western and eastern U.S. populations. Genetic and morphological data will also be compared to European samples collected from six countries. Seeds from the same New York and Vermont populations were germinated and grown in a common greenhouse study by University of Vermont collaborators to correlate various plant and genetic traits with known invasive traits. A second generation experiment was also conducted involving offspring created by selectively crossing parents of different genetic lineages. Plant traits thought to be related to invasiveness showed significant heritability and a strong correlation with the hybrid. A manuscript is in preparation. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. The time to reproductive maturity may be a critical phase in the life cycle of swallow-worts. Data were collected from a long-term field experiment assessing survival and years to flowering of vegetative juveniles of pale and black swallow-wort in different habitats and locations. Individual plants of black swallow-wort began reproducing at a faster rate (beginning at 3-4 years) compared to pale swallow-wort (6-8 years). Many plants, especially pale swallow-wort, took up to 10 years to flower (manuscript in preparation). If swallow-wort biological control is of limited availability, alternative control measures will continue to be needed by land managers. A manuscript was published on a multi-year mowing study of pale swallow- wort. Mowing at least three times within a season prevented seed production beginning the first year but did not reduce pale swallow-wort densities and cover until the fifth year of mowing. Mowing six times per season did not enhance control. Land managers are being advised that they must mow at least three times annually to prevent the production and spread of seeds, and that it will take several years to reduce but not eliminate existing stands of pale swallow-wort. Also, a three-year herbicide trial will be concluded this summer to assess the efficacy of different herbicides in combination with mowing against black swallow- wort. Currently, no data exist on herbicidal control of black swallow- wort. Spotted and meadow knapweed invade a variety of agricultural fields and natural areas, and they are a potentially new and emerging weed problem for the Northeast. Plant population data, including survival of different life stages and seed production, and information on plant phenology were collected over three years from three spotted knapweed and four meadow knapweed field sites in New York. In addition, the presence of biological control agents that were previously released in the region was documented (manuscript in press). A collaborator (University of Vermont) is currently analyzing these data using a plant population modeling approach. Initial results show that six of the seven populations are increasing in size, and that disruption of the seedling and flowering stages may be important for controlling knapweed populations. Knapweed seed bank and seedling emergence studies were established in fall 2018. Data are being collected with a collaborator to determine how many years buried seeds of spotted and meadow knapweed survive and how successfully knapweed seedlings emerge from different burial depths over time. Deeply buried seeds generally did not germinate and had greater than 90% survival after one year. In contrast, most seeds on the soil surface or that were slightly buried germinated within the first year. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Long-term monitoring of vegetation plots occurred prior to release of a biological control agent at several sites in New York State. At some sites, the presence of swallow-wort was correlated with a decline in plant diversity and abundance over time (manuscript in preparation). The biological control agent Hypena opulenta, a moth whose larvae defoliate swallow-worts, was first released in New York State in 2018 at two locations. Two generations per summer were likely based on observations of caged insects. Plant population models developed by us indicated this moth could be an effective agent against slow-growing swallow-wort populations (typically forests), but it may only have a limited impact on faster-growing infestations in fields. Despite some evidence of successful overwintering in spring 2019, the populations of the moth died out during summer 2019. It was simultaneously discovered by ARS scientists at Ithaca that all colonies of the moth in North America were infected with a pathogen. This prevented additional releases in 2019. A new moth colony has been established which is currently being reared for releases this summer. Record of Any Impact of Maximized Teleworking Requirement: Mass rearing and release of an approved biological control agent of swallow-worts, invasive plants in the Northeast, was delayed 2 months. This limited the number of lab-reared insects that could be released this summer and prevented additional natural population increase of the leaf- feeding moth in the field, greatly restricting the size of the population present in the field prior to overwintering. An open-field experiment of a root-feeding beetle, a potential biological control agent of swallow-worts, was planned for this growing season in collaboration with a French ARS scientist. However, growing specific plants for the field study could not occur due to delays in re- opening laboratories as a result of maximized teleworking. An alternate experiment had to be implemented instead.
Impacts
(N/A)
Publications
- Milbrath, L.R., Dolgovskaya, M., Volkovitsh, M., Sforza, R., Biazzo, J. 2020. Photoperiodic response of Abrostola asclepiadis (Lepidoptera: Noctuidae), a candidate biological control agent for swallow-worts (Vincetoxicum, Apocynaceae). Great Lakes Entomologist. 52:71-77.
- Biazzo, J., Milbrath, L.R. 2019. Response of pale swallowwort (Vincetoxicum rossicum) to multiple years of mowing. Invasive Plant Science and Management. 12(3).
- Lachmuth, S., Molofsky, J., Milbrath, L.R., Suda, J., Keller, S.R. 2019. Associations between genomic ancestry, genome size and capitula morphology in the invasive meadow knapweed hybrid complex (Centaurea ÿmoncktonii) in eastern North America. AoBP (Annals of Botany PLANTS). 11(5).
|
Progress 10/01/18 to 09/30/19
Outputs
Progress Report Objectives (from AD-416): Biological control is considered the only long-term control option for many invasive plants. Enhancing the probability of successful biological control requires the identification of not only host-specific biological control agents (although non-specific agents may be feasible in certain situations) but also effective agents. This in turn depends upon a fundamental knowledge of a target weed⿿s biology, genetics, and population dynamics to inform agent selection. Long-term monitoring is needed to verify the specificity and efficacy of field-released agents. It is also important to understand why biological control may not be feasible with currently available agents. Our objectives are to: Objective 1: Evaluate host specificity, efficacy, or other biological traits of biological control agents of invasive plants, especially swallow-wort and eastern knapweeds; and determine the biology, ecology and demography of these weeds. Subobjective 1a: Assess agents of swallow-wort and knapweed. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Approach (from AD-416): European swallow-worts (Vincetoxicum spp.) and knapweeds (Centaurea spp.) are invasive weeds of continued or increasing concern, respectively, in the northeastern U.S. They invade a variety of natural and managed terrestrial ecosystems. A biological control program for swallow-worts has been in development since 2004. This project will evaluate remaining potential insect and fungal agents of swallow-wort for host range and/or life history traits and plant impact in laboratory, greenhouse and (as appropriate) field studies, and implement a biological control agent (a defoliating moth that is anticipated for approval) to control pale and black swallow-wort. Long-term monitoring plots, already established at several sites, will help document the released agent⿿s impact on swallow- wort and resulting responses of invaded plant communities. A remaining knowledge gap of swallow-wort demography (years to first reproduction) will continue to be investigated in a field experiment. The genetics of the fertile hybrid meadow knapweed and demography of northeastern populations of spotted and meadow knapweed will be investigated through field and common garden studies. Initial assessment of a seed-feeding biological control agent on meadow knapweed will be made in the greenhouse to understand its potential impact. Successful implementation of this program should lead to the suppression of the two swallow-wort species in some of the habitats they have invaded, and define future control measures to be implemented against knapweeds. Subobjective 1a: Assess agents of swallow-wort and knapweed. The leaf- feeding moth Abrostola asclepiadis appears to specifically feed and develop on pale and black swallow-wort, and thus could be petitioned for release as a biological control agent. However, laboratory evaluations of French and Russian populations of the moth with Russian collaborators, as well as outdoor rearing of the French moth by a French collaborator, have shown this species will only produce one generation per summer when exposed to day lengths comparable to those of the northeastern United States (manuscript in press). Additional studies of the impact of larval feeding on plants showed that a single defoliation has very limited effects on swallow-worts (manuscript published). Thus, A. asclepiadis will have limited efficacy against pale and black swallow-wort populations, and it should be given a low priority for release. The seed-destroying fly Euphranta connexa continues to be evaluated by Swiss collaborators as a candidate agent for swallow-wort control. Testing protocols continue to be refined to ensure flies are mated and laying eggs in order to generate accurate results. Egg-laying by adult flies and larval development in seed pods are currently being tested on some North American plant species of concern. Previous laboratory tests of the root-feeding beetle Chrysochus asclepiadeus showed that larvae could develop on some North American milkweeds, which are closely related to European swallow-worts. However, adult beetles can be more selective of host plants in the open field. Swiss collaborators conducted an open-field test to determine if adult beetles will or will not colonize and lay eggs on transplanted North American species of milkweeds under natural field conditions. No feeding damage or larvae were found on milkweed plants, but feeding damage and larvae were found on swallow-wort plants. A second open-field test involving common milkweed that has naturalized in France is underway with a French collaborator to more rigorously test the beetle⿿s host preferences. The fungus Sclerotium rolfsii was previously discovered killing pale swallow-wort in New York. It is being evaluated as a potential management option. Changes in the associated plant community and incidence of disease at the discovery site are being documented with a collaborator at Cornell University. A separate two-year field study will be completed later this year to document the survival of the fungus from autumn to the following summer. Results to date indicate fungal survival by mid-summer is poorer with shallow burial of the fungus compared to fungi on the soil surface. The same fungus has recently been documented to cause disease in table beets in New York. Therefore, future studies involving the fungus will need to consider impacts on agricultural crops. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Meadow knapweed is widespread in the Northeast and is considered to be a hybrid between black and brown knapweeds (parent species), all of which were introduced from Europe. A manuscript is nearing publication on the population genetics of 10 New York and 10 Vermont populations. Analyses by collaborators at the University of Vermont revealed two genetic lineages, similar to but not necessarily the two parent species, whose presence varied among the sampled populations. In addition, many hybrid individuals exist as expected and extensive mixing of hybrids has occurred. Populations will be sampled this summer in the Pacific Northwest, where meadow knapweed has long been present, to understand whether this hybrid knapweed resulted from a cross-continental move from Europe or an intracontinental move West to East in the United States. Greenhouse experiments have been conducted by University of Vermont collaborators to correlate traits such as plant size, time to flowering, and number of flower heads with their genetic ancestry. A previous experiment in which plants were grown from field-collected seeds suggested hybrids had greater vigor in plant traits. A second generation experiment has recently been completed involving offspring created by selectively crossing parents of different genetic lineages. Plant traits thought to be related to invasiveness showed significant heritability. A manuscript of the greenhouse experiments is in preparation. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. Plant population data, including survival of different life stages and seed production, are in the process of being collected for a third and final year from three spotted knapweed and four meadow knapweed field sites in New York. A collaborator (University of Vermont) is currently analyzing these data using a plant population modeling approach. Initial results show that most populations are increasing. Key points in the knapweed life cycle will be identified that should be targeted for disruption in order to more effectively control these problematic weeds. Knapweed seed bank and seedling emergence studies were established in fall 2018. Data are being collected to determine how many years buried seeds of spotted and meadow knapweed survive and how successfully knapweed seedlings emerge from different burial depths over time. If swallow-wort biological control is of limited availability, alternative control measures will continue to be needed by land managers. We conducted a seven-year mowing study at a heavily-infested pale swallow- wort field site. Mowing three times per season caused significant reductions in pale swallow-wort densities and percent cover, but generally not until the fifth year of mowing. Seed production was eliminated in all years of the study. Mowing six times per season did not enhance control. Repeated mowing over several years is necessary to reduce, but not eliminate, existing stands of pale swallow-wort (manuscript in revision). In addition, a three-year herbicide trial is in process to assess the efficacy of different herbicides in combination with mowing against black swallow-wort. Currently, no data exist on herbicidal control of black swallow-wort. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. The biological control agent Hypena opulenta, a moth whose larvae defoliate swallow-worts, was first released in New York State in 2018 at two locations. Two generations per summer are likely based on initial observations of caged insects. Successful overwintering has been confirmed from at least one location in 2019. Due to known difficulties mass rearing the moth, additional releases have been delayed to later in the summer. Continued issues with the moth culture may necessitate sourcing moths from field populations already established and increasing in Ontario. Accomplishments 01 Moth will have limited efficacy as a swallow-wort biocontrol agent. The European vines pale and black swallow-wort are invading various habitats in northeastern North America. The leaf-feeding moth Abrostola asclepiadis appears to specifically feed and develop on swallow-worts, and thus could be a useful biological control agent. However, it is also important to estimate its efficacy as an agent. Russian and French researchers in collaboration with an ARS researcher at Ithaca, New York, investigated the moth⿿s response to spring and summer day lengths comparable to those experienced in the northeastern United States. The moth was shown to only produce one generation per summer. The ARS researcher also documented that a single defoliation by the larvae has very limited impacts on swallow-worts. The moth A. asclepiadis will therefore be of limited effectiveness in reducing pale and black swallow-wort populations based on previously produced plant models, and it is recommended that this insect be given a low priority for release. 02 Controlling swallow-worts by mowing. The European perennial plants pale swallow-wort and black swallow-wort have become invasive in eastern North America. Mowing is generally considered an ineffective management tool for introduced swallow-worts, but long-term experiments had not been conducted. An ARS researcher in Ithaca, New York, investigated the response of a severe pale swallow-wort infestation to mowing three or six times per year over six years. Mowing at least three times within a season prevented seed production beginning the first year but did not reduce pale swallow-wort densities and cover until the fifth year of mowing. Mowing six times per season did not enhance control. Land managers are being advised that they must mow at least three times annually to prevent the production and spread of seeds, and that it will take several years to reduce but not eliminate existing stands of pale swallow-wort. Similar results would likely apply to other perennial non-woody weed species.
Impacts
(N/A)
Publications
- Milbrath, L.R., Biazzo, J., Ditommaso, A., Morris, S.H. 2019. Impact of Abrostola asclepiadis combined with other stressors on invasive swallow- worts (Vincetoxicum species). Biological Control. 130:118-126.
|
Progress 10/01/17 to 09/30/18
Outputs
Progress Report Objectives (from AD-416): Biological control is considered the only long-term control option for many invasive plants. Enhancing the probability of successful biological control requires the identification of not only host-specific biological control agents (although non-specific agents may be feasible in certain situations) but also effective agents. This in turn depends upon a fundamental knowledge of a target weed�s biology, genetics, and population dynamics to inform agent selection. Long-term monitoring is needed to verify the specificity and efficacy of field-released agents. It is also important to understand why biological control may not be feasible with currently available agents. Our objectives are to: Objective 1: Evaluate host specificity, efficacy, or other biological traits of biological control agents of invasive plants, especially swallow-wort and eastern knapweeds; and determine the biology, ecology and demography of these weeds. Subobjective 1a: Assess agents of swallow-wort and knapweed. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Approach (from AD-416): European swallow-worts (Vincetoxicum spp.) and knapweeds (Centaurea spp.) are invasive weeds of continued or increasing concern, respectively, in the northeastern U.S. They invade a variety of natural and managed terrestrial ecosystems. A biological control program for swallow-worts has been in development since 2004. This project will evaluate remaining potential insect and fungal agents of swallow-wort for host range and/or life history traits and plant impact in laboratory, greenhouse and (as appropriate) field studies, and implement a biological control agent (a defoliating moth that is anticipated for approval) to control pale and black swallow-wort. Long-term monitoring plots, already established at several sites, will help document the released agent�s impact on swallow- wort and resulting responses of invaded plant communities. A remaining knowledge gap of swallow-wort demography (years to first reproduction) will continue to be investigated in a field experiment. The genetics of the fertile hybrid meadow knapweed and demography of northeastern populations of spotted and meadow knapweed will be investigated through field and common garden studies. Initial assessment of a seed-feeding biological control agent on meadow knapweed will be made in the greenhouse to understand its potential impact. Successful implementation of this program should lead to the suppression of the two swallow-wort species in some of the habitats they have invaded, and define future control measures to be implemented against knapweeds. Objective 1: The leaf-feeding moth Abrostola asclepiadis has been shown by a French collaborator to produce only one generation per summer when reared outdoors for two years under naturally-changing daylengths and at a latitude similar to New York State. This result complements previously- completed laboratory studies on diapause in the United States. Thus, as a candidate biological control agent, the moth will have a limited impact on pale and black swallow-wort because of the plants ability to regrow following insect damage. A manuscript is under review that reports on the feeding impact on pale and black swallow-wort of the moth Abrostola asclepiadis both alone and in combination with different levels of shading or plant competition. Shading or competition alone reduced plant performance, in some cases comparable to insect damage. However, the different sources of stress did not appear to interact and therefore did not enhance the effectiveness of the moth. A seed-destroying fly of swallow-worts continues to be evaluated by Swiss collaborators. Testing protocols are being refined to ensure insects are mated in order to document if female flies will lay eggs, and larvae will successfully develop, on various plant species closely related to the swallow-worts. Swiss collaborators are also conducting an open-field test of a root-feeding beetle to determine if female beetles will or will not colonize and lay eggs on North American species of milkweeds. Depending on the results, additional screening of the insects may occur overseas or in quarantine in the U.S. A two-year study is in progress to document the survival in the soil of a disease-causing fungus of swallow-worts that was discovered in New York. Fungal survival by mid-summer is poor with shallow burial of the fungus, whereas fungal survival on the soil surface is around 50%. Additional host-range tests of the fungus were delayed due to the retirement of a key collaborator; the tests may be implemented next year. Data collection has ended for long-term field experiments assessing survival and time to reproductive maturity of vegetative juveniles of pale and black swallow-wort in different habitats and locations. Individual plants of black swallow-wort began reproducing at a faster rate (beginning at 3-4 years) compared to pale swallow-wort (6-8 years). Many plants, especially pale swallow-wort, took up to 10 years to flower. This result confirms previous greenhouse and outdoor experiments on the rapid maturation rate of black swallow-wort. In an effort to document the efficacy of alternative control measures should biocontrol be of limited availability, a final year of data is being collected for a long-term mowing study at a heavily-infested pale swallow-wort field site. Preliminary analyses suggest that high-frequency mowing (three or six times per season) may reduce pale swallow-wort densities to a limited extent but only after several years of mowing. In addition, a two-year herbicide trial is being established this summer to assess the efficacy of different herbicides in combination with mowing against black swallow-wort. Currently, no data exist on herbicidal control of black swallow-wort. A plant population modelling study of pale and black swallow-wort, including projected outcomes of biological control efforts, and a swallow- wort seed dispersal study have been published. Plant population data, including survival of different life stages and seed production, are in the process of being collected for a second year from three spotted knapweed and four meadow knapweed field sites in New York. These data will be used in plant population models to better define effective control programs. In addition, knapweed seed bank and seedling emergence studies will be established later this summer to determine how many years seeds will take to germinate at different burial depths as well as the longevity of buried seeds. A manuscript will be submitted on the population genetics of 10 New York and 10 Vermont populations of what had been initially identified as meadow knapweed. Meadow knapweed is considered to be a hybrid between black and brown knapweeds. Analyses indicate that three genetic lineages are present, although this varied among the sampled populations, suggesting that the hybrid and forms very similar to the parental species still exist in the field. Extensive mixing among the groups has occurred. In addition, genome size and a subset of flower head traits are correlated with the genetic ancestry. Various plant growth traits measured in a greenhouse study of the different plant lineages, which are known to be associated with invasiveness, also showed strong correlations with the hybrid forms. A second manuscript is in preparation regarding the greenhouse study. Objective 2: A biological control agent, the moth Hypena opulenta, was approved for field release in September 2017. Releases of larvae, which feed on the leaves of swallow-worts, have occurred in June 2018 at two locations in New York State. Additional releases are planned with collaborators for other locations in 2018. A laboratory colony is also being maintained for more extensive releases in 2019.
Impacts
(N/A)
Publications
- Milbrath, L.R., Davis, A.S., Biazzo, J. 2018. Identifying critical life stage transitions for biological control of long-lived perennial Vincetoxicum species. Journal of Applied Ecology. 55:1465-1475.
- Ditommaso, A., Stokes, C.A., Cordeau, S., Milbrath, L.R., Whitlow, T.H. 2018. Seed dispersal ability of the invasive perennial vines Vincetoxicum nigrum and Vincetoxicum rossicum. Invasive Plant Science and Management. 11:10-19.
|
Progress 10/01/16 to 09/30/17
Outputs
Progress Report Objectives (from AD-416): Biological control is considered the only long-term control option for many invasive plants. Enhancing the probability of successful biological control requires the identification of not only host-specific biological control agents (although non-specific agents may be feasible in certain situations) but also effective agents. This in turn depends upon a fundamental knowledge of a target weed�s biology, genetics, and population dynamics to inform agent selection. Long-term monitoring is needed to verify the specificity and efficacy of field-released agents. It is also important to understand why biological control may not be feasible with currently available agents. Our objectives are to: Objective 1: Evaluate host specificity, efficacy, or other biological traits of biological control agents of invasive plants, especially swallow-wort and eastern knapweeds; and determine the biology, ecology and demography of these weeds. Subobjective 1a: Assess agents of swallow-wort and knapweed. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Approach (from AD-416): European swallow-worts (Vincetoxicum spp.) and knapweeds (Centaurea spp.) are invasive weeds of continued or increasing concern, respectively, in the northeastern U.S. They invade a variety of natural and managed terrestrial ecosystems. A biological control program for swallow-worts has been in development since 2004. This project will evaluate remaining potential insect and fungal agents of swallow-wort for host range and/or life history traits and plant impact in laboratory, greenhouse and (as appropriate) field studies, and implement a biological control agent (a defoliating moth that is anticipated for approval) to control pale and black swallow-wort. Long-term monitoring plots, already established at several sites, will help document the released agent�s impact on swallow- wort and resulting responses of invaded plant communities. A remaining knowledge gap of swallow-wort demography (years to first reproduction) will continue to be investigated in a field experiment. The genetics of the fertile hybrid meadow knapweed and demography of northeastern populations of spotted and meadow knapweed will be investigated through field and common garden studies. Initial assessment of a seed-feeding biological control agent on meadow knapweed will be made in the greenhouse to understand its potential impact. Successful implementation of this program should lead to the suppression of the two swallow-wort species in some of the habitats they have invaded, and define future control measures to be implemented against knapweeds. Objective 1: Evaluate biocontrol agents and biology of swallow-worts and knapweeds. Laboratory studies indicate that different populations of the leaf-feeding moth Abrostola asclepiadis, which was imported from Europe into U.S. quarantine as a potential biological control agent of pale and black swallow-wort, will likely only have one generation per year. A French field study continues with a collaborator for a second year to determine how many generations the moth may have when reared outdoors under naturally-changing daylengths at a latitude similar to the northeastern U.S. Currently, it appears that a single generation occurs in the field. This information will help elucidate the maximum amount of damage the moth can inflict within a growing season. A greenhouse study examining the combined impact of plant competition and defoliation by a French population of the moth on pale and black swallow-wort is nearing completion. This study complements a previous experiment involving combinations of defoliation and shading. Results of the two studies will inform whether different types of environmental stress can enhance the damage of a leaf-feeding biocontrol agent and thus increase its effectiveness in reducing swallow-wort populations over time. A seed-destroying fly of swallow-worts is currently being evaluated by Swiss collaborators. We are examining if the adult fly will lay eggs, and larvae successfully develop, on various closely-related plants to the swallow-worts. A disease of swallow-worts had previously been shown to kill 67-100% of swallow-wort seedlings. On-going laboratory assays with a collaborator indicate that the pathogen is also highly virulent and able to cause disease on adult flowering plants. In separate field studies, data are being collected at a New York site on pathogen infection rates over time of pale swallow-wort seedlings and adult plants and on potential changes in the existing plant community as swallow-wort declines due to the pathogen. An overwintering survival study of the pathogen was delayed due to the retirement of a key collaborator; the study is expected to be implemented later this year. Data collection continues for long-term field experiments assessing survival and growth of vegetative juveniles of pale and black swallow- wort in different habitats and locations. The time to reproductive maturity may be a critical phase in the life cycle of swallow-worts. To date, individual plants of black swallow-wort begin reproducing at a faster rate (beginning at 3-4 years) compared to pale swallow-wort (6 years or more). Further, few pale swallow-wort individuals have reached a flowering state across several locations, whereas most black swallow-wort juveniles have already done so. In an effort to document the efficacy of alternative control measures should biocontrol not be available, a long-term mowing study continues for a sixth and final season at a heavily-infested pale swallow-wort field site. Preliminary analyses suggest that a high frequency of mowing (three or six times per season) does not influence pale swallow-wort densities. A report of potential resistance of pale swallow-wort to a commonly used herbicide in New York was not supported in a laboratory assay, suggesting that issues with the application of the herbicide may be a more likely explanation for lack of herbicidal control. Thus, herbicides are still a viable control option. Manuscripts for a plant population modelling study of pale and black swallow-wort have been published or are under review. A multi-year seed bank study of swallow-wort has been published, and a manuscript on a previously conducted swallow-wort seed dispersal study is in preparation. Spotted and meadow knapweed are potentially new and emerging weed problems in agricultural fields and natural areas of the Northeast. Plant population data, including survival of different plant stages and seed production, are currently being collected from three spotted knapweed and four meadow knapweed field sites in New York. These data will be used in plant population models to better define effective control programs. In addition, the presence of knapweed biological control agents that were previously released in the region is being documented. Preliminary knapweed seed bank and seedling emergence studies were established. Results will help determine the methods needed when implementing the final experiments in 2018. Genetic libraries have been created by Vermont collaborators from leaf samples previously collected from 10 New York and 10 Vermont populations of meadow knapweed. Population genetic analyses are in process. Initial results indicate that three genetic groups are present, extensive mixing among the groups has occurred, and genome size is correlated with genetic ancestry. Seeds, collected from the same New York and Vermont populations, were germinated and grown in a common greenhouse study, and various plant traits were measured in order to correlate these physical traits, the plants� genetic identities, and known invasive traits. Crosses were also made between these greenhouse grown plants, and the resulting seeds were germinated and grown in a second common greenhouse study. Physical traits were again measured and leaves were sampled for genetic analyses. Manuscripts are in preparation for the first greenhouse study and genetic analyses. Objective 2. Monitor released biocontrol agents. Long-term monitoring of vegetation plots has been completed at several sites slated for the release of swallow-wort biological control agents. A petition submitted by colleagues for U.S. release of a moth biological control agent (Hypena opulenta) remains under review but is expected to be approved later this year. Open field releases of the moth are expected to occur in spring 2018. Final permissions are being obtained from local land managers for New York releases pending receipt of federal and state permits. Plant population models developed by ARS researchers in Ithaca, New York indicate this moth could be an effective agent against slow-growing swallow-wort populations (typically forests), but it may only have a limited impact on faster-growing infestations in fields. Accomplishments 01 Swallow-wort population model helps guide biocontrol. The European perennial plants pale swallow-wort and black swallow-wort have become invasive in eastern North America. For biological control to be successful as a management tool, biocontrol agents must be capable of reducing swallow-wort populations to low levels. ARS researchers at Ithaca, New York and Urbana, Illinois developed plant population models of the two species that identified key points of the plants� life cycles to be targeted and how much damage an agent must inflict for successful control to occur. Leaf-feeding moths or seed-destroying flies are promising for controlling slow-growing populations of the weeds (forest and some field) and are recommended for screening and eventual release as biological control agents. However, fast-growing field populations will not be controlled with these insects. Instead, it is recommended that land managers integrate other control tactics for successful management of these weeds. 02 Swallow-wort seeds are short-lived in soil. Weed control by land managers and farmers can be hampered by new plants emerging from long- lived seeds in the soil (seed bank). A multi-year seed bank study of pale and black swallow-wort, two invasive species of the Northeast, showed that buried seeds do not survive more than 2-3 years. Also, if practical, burial of seeds up to 10 cm deep for pale swallow-wort, and more than 10 cm deep for black swallow-wort, will prevent seedling emergence. If land managers focus on limiting swallow-wort seed production and seedling establishment for at least three years, restoration of affected areas will have a much greater likelihood of success.
Impacts
(N/A)
Publications
- Ditommaso, A., Milbrath, L.R., Morris, S.H., Mohler, C.H., Biazzo, J. 2017. Seedbank dynamics of two swallowwort (Vincetoxicum) species. Invasive Plant Science and Management. 10(2):136-142. doi: 10.1017/inp.2017.10.
- Milbrath, L.R., Davis, A.S., Biazzo, J. 2017. Demography of invasive black and pale swallow-wort populations in New York. Northeastern Naturalist. 24:37-53.
- Dolgovskaya, M., Volkovitsh, M., Reznik, S., Moseyko, A.G., Milbrath, L.R. 2016. Host specificity of Asian Chrysochus Chevr. in Dej. (Coleoptera, Chrysomelidae, Eumolpinae) and their potential use for biological control of invasive Vincetoxicum species. Entomological Review (Entomol Rev). 96:826-830.
- Milbrath, L.R., Nechols, J.R. 2014. Plant-mediated interactions: considerations for agent selection in weed biological control programs. Biological Control. 72:80-90.
- Ditommaso, A., Milbrath, L.R., Bittner, T., Wesley, F.R. 2013. Pale Swallowwort (Vincetoxicum rossicum) response to cutting and herbicides. Journal of Invasive Plant Science and Management. 6:381-390.
|
Progress 10/01/15 to 09/30/16
Outputs
Progress Report Objectives (from AD-416): Biological control is considered the only long-term control option for many invasive plants. Enhancing the probability of successful biological control requires the identification of not only host-specific biological control agents (although non-specific agents may be feasible in certain situations) but also effective agents. This in turn depends upon a fundamental knowledge of a target weed�s biology, genetics, and population dynamics to inform agent selection. Long-term monitoring is needed to verify the specificity and efficacy of field-released agents. It is also important to understand why biological control may not be feasible with currently available agents. Our objectives are to: Objective 1: Evaluate host specificity, efficacy, or other biological traits of biological control agents of invasive plants, especially swallow-wort and eastern knapweeds; and determine the biology, ecology and demography of these weeds. Subobjective 1a: Assess agents of swallow-wort and knapweed. Subobjective 1b: Elucidate the genetic structure of knapweed populations in the Northeast. Subobjective 1c: Determine demographic rates for swallow-wort and knapweed. Objective 2: Release approved biological control agents and evaluate their establishment, phenology, and impact on weed populations and other flora, for invasive plants such as swallow-wort. Approach (from AD-416): European swallow-worts (Vincetoxicum spp.) and knapweeds (Centaurea spp.) are invasive weeds of continued or increasing concern, respectively, in the northeastern U.S. They invade a variety of natural and managed terrestrial ecosystems. A biological control program for swallow-worts has been in development since 2004. This project will evaluate remaining potential insect and fungal agents of swallow-wort for host range and/or life history traits and plant impact in laboratory, greenhouse and (as appropriate) field studies, and implement a biological control agent (a defoliating moth that is anticipated for approval) to control pale and black swallow-wort. Long-term monitoring plots, already established at several sites, will help document the released agent�s impact on swallow- wort and resulting responses of invaded plant communities. A remaining knowledge gap of swallow-wort demography (years to first reproduction) will continue to be investigated in a field experiment. The genetics of the fertile hybrid meadow knapweed and demography of northeastern populations of spotted and meadow knapweed will be investigated through field and common garden studies. Initial assessment of a seed-feeding biological control agent on meadow knapweed will be made in the greenhouse to understand its potential impact. Successful implementation of this program should lead to the suppression of the two swallow-wort species in some of the habitats they have invaded, and define future control measures to be implemented against knapweeds. Objective 1: Laboratory studies continue to characterize the daylength response of different populations of a species of leaf-feeding moth (Abrostola asclepiadis) imported into U.S. quarantine as a potential biological control agent of pale and black swallow-wort. A companion field study involving a French population of the moth has been established in France to determine the moth�s response under naturally- changing daylengths. This information will help elucidate the potential number of generations the moth may have per year and thus how much defoliation damage it may cause. A study examining the impact of defoliation by a Russian population of the moth on pale and black swallow-wort under different light levels has been completed. Results have been incorporated into a previously completed swallow-wort population model for projections of the moth�s ability to control different swallow-wort infestations. Swallow-wort infestations in forests and a few open fields may be controlled with two generations of the moth during the summer. However, the moth�s effectiveness will decrease if it only produces one generation per year. A seed-destroying fly is currently being evaluated by Swiss collaborators. They are examining if the adult fly will lay eggs, and larvae successfully develop, on various closely-related plants in addition to the swallow-worts. Research on a disease that can kill swallow-worts has been postponed due to a change in collaborator. Spotted and meadow knapweed invade a variety of agricultural fields and natural areas, and they are a potentially new and emerging weed problem for the Northeast. Plant population studies have been established at three spotted knapweed and four meadow knapweed field sites. Information on plant phenology, seed viability, population densities, and seed numbers in the soil seed bank have been collected. In addition, the presence of biological control agents that were previously released in the region is being documented. Leaf, seed, and flower head samples were collected from 10 New York and 10 Vermont populations of meadow knapweed, which is a fertile hybrid between brown and black knapweed. Vermont collaborators have extracted DNA from all samples and genetic libraries are being created. Seeds from all sampled populations have been grown in a common greenhouse study and various plant traits were measured from the resulting plants. Correlations between these physical traits, genetic identities, and known invasive traits will be conducted by the Vermont collaborators. Data collection continues for a long-term field experiment assessing survival and growth of vegetative juveniles of pale and black swallow- wort in different habitats which may be a critical phase in the life cycle of swallow-worts. Apart from the first year (2008), black swallow- wort survival has been greater than pale swallow-wort across the three habitats (old field, forest edge, forest understory). Low plant survival in recent years (<10%) may be due to both a dense cover of resident vegetation in the old field habitat and leaf litter in the forest as well as wetter conditions at the site than swallow-wort tolerates. Black swallow-wort has been confirmed to have a shorter juvenile phase than pale swallow-wort, although several remaining plants of both species have yet to flower and produce seed after eight years. A multi-year seed bank study of swallow-wort has been completed and a manuscript is in preparation. The seed bank dynamics for these invasive species was poorly known. The majority of seedling emergence occurred during the first year (92% in 2012), and no new seedlings emerged after the second year. Also, no buried, viable seed was recovered after the second year. Both pale and black swallow-wort appear to have a short- lived seed bank. In addition, although many seedlings died before reaching the soil surface when sown at 5 or 10 cm depths, one pale swallow-wort and many black swallow-wort seedlings did successfully emerge from 10 cm which was not expected. Manuscripts are in preparation for a plant population modelling study of pale and black swallow-wort. A long-term mowing study continues for a fifth season at a heavily- infested pale swallow-wort field site in an effort to document the efficacy of alternative control measures should biocontrol not be a viable option. Preliminary analyses have yet to show a change in pale swallow-wort densities from high frequency mowing (three or six times per season). Objective 2: Long-term monitoring of vegetation plots will continue next season at several sites slated for the future release of swallow-wort biological control agents. A petition submitted by colleagues for U.S. release of a moth biological control agent remains under review but is expected to be approved. Final permissions are being obtained from local land managers for New York releases pending receipt of federal and state permits. Plant population models developed by researchers in Ithaca, New York indicate this moth could be an effective agent against swallow-wort in forests but may only have a limited impact on infestations in fields. Accomplishments 01 Biological control potential of a moth against swallow-wort in forests. Pale and black swallow-wort, European twining vines, have invaded forest and field habitats in northeastern North America. A moth (Hypena opulenta) collected from the Ukraine, whose larvae eat the leaves of swallow-wort, has been released in Canada and may be released in the U. S. but no information existed on its impact on swallow-wort plants under low light conditions typical for forest understories. ARS researchers in Ithaca, New York determined in a greenhouse study that increasing amounts of defoliation and shading, but not necessarily frequency of defoliation, reduced plant biomass and seed production of both species of swallow-wort. However, even severe defoliation generally caused little mortality of seedlings. Land managers are being advised that Hypena opulenta must completely and repeatedly defoliate swallow-wort every year for this biological control agent to suppress forest infestations of swallow-wort. 02 Swallow-worts are highly tolerant to multiple years of damage. The European vines pale and black swallow-wort are invading various habitats in northeastern North America. Different control tactics have been investigated in studies of one to two year�s duration, but it was unclear how these plants might respond to multiple years of defoliation by a biological control agent or different frequencies of mowing. ARS researchers and university collaborators in Ithaca, New York determined in a field experiment that swallow-wort plants continued to grow larger and in most cases produced abundant seed every year for six years despite artificially removing leaves or clipping plants to varying degrees. Clipping plants four times every season was the only type of experimental damage that prevented plant growth and seed production, but it did not kill the plants. The limited effect of the severest defoliation treatment (complete leaf removal twice per season) calls into question the potential efficacy of a defoliating insect against swallow-wort populations growing under full sun conditions. The only benefit of a long-term mowing program, which needs to occur at least twice per season, will be to eliminate seed production. 03 Swallow-wort chemical unlikely to harm other plants in the field. Antofine is a chemical produced by the invasive weeds pale and black swallow-wort that can inhibit the growth of other plants in laboratory studies giving swallow-wort a potential competitive advantage. ARS researchers in Ithaca, New York have found substantial amounts of antofine in seeds, seedlings, and adult plants but it was not present in detectible amounts in soil samples collected over two growing seasons at four different field sites infested with pale or black swallow-wort. Further study showed that swallow-wort roots exude very low levels of antofine and that it readily breaks down into inactive compounds. Antofine does not appear to promote the invasion of swallow- worts into plant communities through the inhibition of other plants under natural conditions.
Impacts
(N/A)
Publications
- Milbrath, L.R., Ditommaso, A., Biazzo, J., Morris, S.H. 2016. Tolerance of Swallowworts (Vincetoxicum spp.) to multiple years of artificial defoliation or clipping. Invasive Plant Science and Management. 9:1-11.
- Milbrath, L.R., Biazzo, J. 2016. Impact of the defoliating moth Hypena opulenta on invasive swallow-worts (Vincetoxicum species) under different light environments. Biological Control. 97:1-12.
|
|