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United States Department of Agriculture

Agricultural Research Service

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Location: Emerging Pests and Pathogens Research

2012 Annual Report

1a. Objectives (from AD-416):
Determine the effect of habitat and repeated foliar damage on the growth, reproduction, and survival of black and pale swallow-wort plants, and document the survival and longevity of swallow-wort seed in the soil seed bank.

1b. Approach (from AD-416):
Established seedlings of pale and black swallow-wort will be tagged within three habitat types and annually censused for survival, growth and time to first seed production. Mature plants of pale and black swallow-wort will be planted into a common garden and receive damage treatments consisting of clipping, 50% or 100% defoliation at different frequencies over six years. Various growth and reproductive parameters will be measured. Subsets of plants will be harvested during that time to assess changes in plant biomass. Seed of pale and black swallow-wort will be placed at various depths into pots sunken into the ground and assessed for germination and survival rates over four years.

3. Progress Report:
Various studies of pale and black swallow-wort biology are being conducted to help determine what factors affect their population growth and spread and what life stages should be targeted for disruption through biological control. Data collection continues for a field study established in fall 2007 of the effect of habitat (field, forest edge, and forest interior) on swallow-wort seedling survival, growth, and time to first flower. After the fourth season of growth (2011), survival of black swallow-wort (26%) was greater than pale swallow-wort (6%). Juvenile black swallow-wort plants remained approximately twice as tall as pale swallow-wort plants. Nine black swallow-wort plants in the field habitat flowered in 2011 with seven producing seeds. Low survival is attributed to both a dense cover of resident vegetation in the old field as well as wetter conditions than swallow-wort tolerates. A long-term field experiment examining the effects of different types and frequencies of foliage removal on pale and black swallow-wort performance continues. The eight damage treatments are: 50% defoliation (all new leaves cut in half widthwise plus stem tips cut) or 100% defoliation once (July) or twice (June & July) each season, clipping stems 8 cm above soil level once (June), twice (June & July) or four times (May, June, July, Aug.) each season, and undamaged control plants. Data analysis will commence after another season of the experiment is finished. Prior to the release of biological control agents, accurate information on traditional weed control methods will be needed by land managers for swallow-wort control in both old field and forest understory habitats. We are nearing submission of an article detailing a two-year (2008-2009) herbicide and mowing study that we’ve previously reported for pale swallow-wort in an old field and adjacent forest understory site near Ithaca, NY. Sites were mowed in early July and mowed again or sprayed in late August with glyphosate or a high or low rate of either triclopyr triethylamine salt or triclopyr butoxyethyl ester. The most effective herbicide treatments differed between the two habitat types. High rate triclopyr butoxyethyl ester reduced old field pale swallow-wort cover by 88% and stem (> 5cm) density by 87% after two years of treatments. High rate triclopyr triethylamine salt effectively decreased long and short (< 5cm) stem densities by 86 and 96%, respectively. Mowing significantly increased pale swallow-wort cover and stem densities. In the forest understory habitat, glyphosate and high rates of triclopyr triethylamine salt or triclopyr butoxyethyl ester were most effective in reducing pale swallow-wort cover (80, 78, and 76%, respectively). In contrast to results in the old field habitat, pale swallow-wort cover was reduced by 20% in plots that were mowed twice both years. The high rates of triclopyr triethylamine salt and triclopyr butoxyethyl ester decreased long and short stem densities by 91% and 37%, respectively. Interestingly, low application rates of triclopyr triethylamine salt and triclopyr butoxyethyl ester increased densities of short stemmed (< 5 cm) pale swallow-wort. Our findings suggest that integrated techniques may control pale swallow-wort but that effective management strategies are habitat dependent. A multi-year seed bank study was initiated in fall 2011 to assess the longevity of seed of pale and black swallow-wort at different burial depths. Data are currently being collected for the first year of the study. A greenhouse experiment is being conducted to supplement a previous study of the photosynthetic abilities of pale and black swallow-wort. Specifically, this experiment will measure the ability of black swallow-wort to photosynthesize under very low light conditions, similar to that found in heavily-shaded forest understories. Black swallow-wort has not been observed infesting such habitats normally. The data obtained in this study will supplement data from previous work and will be added to a draft manuscript.

4. Accomplishments

Last Modified: 07/27/2017
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