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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Biological Control of Swallow-Worts, Invasive Weeds of the Northeastern United States

Location: Biological Integrated Pest Management Unit

2011 Annual Report


1a.Objectives (from AD-416)
1: Evaluate the risk posed by candidate biological control agents of swallow-worts. 2: Discover biological attributes of swallow-worts that contribute to their invasiveness and identify points of attack for enhancing biological control efficacy. 2a: Delineate the potential contributions of swallow-worts’ phytotoxic constituents to its invasiveness. 2b: Determine demographic rates for pale and black swallow-wort. 2c: Determine how swallow-wort responds to multiple seasons of repeated clipping/artificial defoliation.

3: Release and evaluate establishment and initial impact of biological control agents of swallow-worts. 3a: Document pre- and post-release densities of swallow-wort and assess changes in associated vegetation. 3b: Assess agent establishment.


1b.Approach (from AD-416)
Foreign exploration will identify damaging natural enemies of swallow-worts in their native range. The fundamental host range of candidate biological control agents will be determined overseas and in quarantine. Swallow-wort tissue extracts will be assessed for allelopathic activity, a possible mechanism of invasion. Field-based plant demography studies will identify life stage transitions that strongly affect population growth rates of these invasive plants. Knowledge of these critical transitions will be used to guide the selection of potentially effective agents, a new approach for weed biological control in the U.S. Long-term defoliation/clipping studies will be conducted to document the rate of plant decline. Comparative surveys of areas infested and uninfested by pale swallow-wort will document its impact on plant density, cover and species richness of native ecosystems both before and after the release of approved biological control agents. Additional permanent monitoring sites will document changes in pale and black swallow-wort densities before and after release of agents. Establishment success of newly released agents will be evaluated.


3.Progress Report
This report documents research toward the protection of natural and managed ecosystems from swallow-worts (SW), terrestrial weeds. Foreign surveys and host range testing of potential insect biological control agents of SW continue in collaboration with French, Russian, and Chinese scientists. Root-feeding beetles studied to date appear to present a risk to native milkweeds. A leaf-feeding moth was imported into U.S.-quarantine and developed on one out of 62 non-target plants (Objective 1). A third season of field data is being collected for the pale and black SW life-history model. Four pale SW and two black SW populations are being tracked, including in open field and forest habitats. Analyses will be conducted to identify potential weak links in the plants’ life cycles and thereby guide the selection of effective biological control agents. Data collection continues for a field study established in fall 2007 of the effect of habitat (field, forest edge, and forest interior) on SW seedling and juvenile survival, growth, and time to first flower. Survival of black SW was greater than pale SW. Juvenile black SW remained 2.5-3.5 times taller than pale SW. To date, only four black SW plants have flowered but none have produced seed. A long-term field experiment examining the effects of different types and frequencies of foliage removal on field-grown SW performance continues. Stem lengths and mass were unchanged from 2009 to 2010. Root dry mass increased from 2009 to 2010 in all damage treatments except plants clipped four times – their root mass was unchanged. Branching generally increased with increasing damage frequency. Viable seed production decreased for black SW, but not pale SW, clipped 2x or 4x compared to controls. Pale and black swallow-wort display a high tolerance to above-ground tissue loss in high-light environments. A two-year herbicide/mowing study for pale SW was conducted in an old field and adjacent forest understory near Ithaca, NY. After two years, SW cover and density of large SW stems (>5cm) in the old field decreased from initially measured values with herbicidal treatments but increased with mowing. Small (<5cm) stem density decreased in all treatments. In the forest understory, reductions in cover and large stem density occurred in all treatments. Small stem density changes were variable depending on the herbicide used. Findings suggest that management of pale SW using herbicides in combination with mowing can be effective but may vary with habitat. A preliminary trial was conducted and modifications have been made to a soil-seed bank study that will be started in fall 2011. Soil samples continue to be collected at monthly intervals for a second growing season at two separate sites for both pale SW and black SW for analysis to detect concentrations of suspected allelochemicals. Following a report of a declining pale SW population, further analysis indicated the presence of a fungal infection. The fungus has been isolated from multiple infected plants and is undergoing morphological and molecular identification (Objective 2). Long-term monitoring of vegetation plots continued for a fourth year (Objective 3).


Review Publications
Averill, K.M., Ditommaso, A., Mohler, C.L., Milbrath, L.R. 2010. Establishment of the invasive perennial Vincetoxicum rossicum across a disturbance gradient in New York State, USA. Plant Ecology. 211:65-77. DOI: 10.1007/s11258-010-9773-2.

Averill, K.M., Ditommaso, A., Mohler, C.L., Milbrath, L.R. 2011. Survival, growth, and fecundity of the invasive swallow-worts (Vincetoxicum rossicum and V. nigrum) in New York State. Journal of Invasive Plant Science and Management. 4:198-206. DOI: 10.1614/IPSM-D-10-00034.1.

Last Modified: 12/19/2014
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