Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2008
Publication Date: 10/16/2008
Citation: Milbrath, L.R. 2008. Growth and reproduction of invasive Vincetoxicum rossicum and V. nigrum under artificial defoliation and different light environments. Botany. 86:1279-1290.
Interpretive Summary: Pale and black swallow-wort are exotic vines that have become increasingly invasive in various habitats in the northeastern United States and southeastern Canada. Because neither species appears to be damaged by plant-feeding insects or diseases in North America, it is unclear how they will respond to damage from natural enemies that may be introduced for their control. I therefore artificially defoliated seedlings and mature plants of pale and black swallow-wort grown under different levels of light. Increasing the frequency of defoliation caused greater reductions in plant growth and reproduction. Complete defoliation caused many mature plants and most seedlings to die under low light, whereas only one defoliated seedling died under high light. Defoliation may be effective in controlling these invasive plants if they are growing in a forest understory but appears to be of more limited usefulness in high light environments such as pastures.
Technical Abstract: The exotic vines Vincetoxicum rossicum (Kleopow) Barbar. and V. nigrum (L.) Moench have become increasingly invasive in low- and high-light habitats in North America and a biological control program is being developed. These plants experience little damage in North America, so it is unclear how they might respond to introduced herbivores. I conducted an artificial defoliation study on seedlings and mature plants of V. rossicum and V. nigrum grown under different light environments. Under high light, V. nigrum produced more seed and allocated more resources to above-ground tissue (root:shoot ratios < 1), whereas V. rossicum allocated more resources to roots with root:shoot ratios of 1.9 for mature plants and > 3 for seedlings. These differences disappeared with shading. Increasing frequencies of 100% defoliation caused greater reductions in biomass and seed production for both species and plant stages. Shading further reduced biomass and no seed was produced. Defoliation of shaded, but not unshaded, plants caused high mortality. Additional cutting of stem tips increased branching only. Defoliation may be effective against Vincetoxicum plants growing in low-light environments such as forest understories but appears to be of more limited value in high-light environments unless repeated defoliation occurs.