Provided by the Western
Massachusetts Master Gardener Association
www.wmassmastergardeners.org.
Gardening
Topic for September 2003
Space Invaders
By Carole Fuller, Master Gardener Intern
Science-fiction films often share a crucial plot device: the alien invaders' success rests on humans not recognizing the real danger until the invaders have achieved overwhelming numbers.
Gardeners certainly spot Japanese beetles as they select our brightest fruit and swelling rosebuds for a meal that continues from June to September. What is harder to notice (except for Loosestrife in full bloom), is the advance of invasive plants, which are estimated to infest more than 100 million acres and expand their range by 8-20% annually (an area twice the size of the state of Delaware).
Invasive plants are not just weeds; they are plants that cause economic and environmental harm by establishing a dominant monoculture that gradually eliminates other plants, such as the replacement of economically significant sugar maple trees with Norway maples or elimination of young trees by thickets of Buckthorn. Monarch butterflies are sometimes tricked by Black Swallowwort’s resemblance to Milkweed, although the Swallowwort is poisonous to them. Migratory songbird declines may be linked, in part, to habitat destruction by invasives.
Non-native species cost the country more than $138 billion annually, and invasive plants account for nearly $35 billion of that sum. Cost studies usually include dollar figures for economic damages and control, not the environmental and health costs, which would raise the total sum significantly.
For the past two years, in a joint effort of the New England Wild Flower Society, University of Connecticut, and the New England Invasive Plant Group (a consortium of 45 horticultural and environmental groups), a corps of trained volunteers has been mapping public lands in an effort to assess the penetration of various invasive plants, particularly in areas containing threatened native species. The Invasive Plant Atlas of New England Project (IPANE) is constructing a database of New England's invasive plants in order to educate the public and appropriate officials on management and control to salvage or conserve affected lands.
In a botanical version of the red car phenomenon (once you buy one, they become highly visible everywhere) it is impossible to travel more than a few hundred yards in any direction without encountering invasive plants, once you can spot them more easily. Although some plants, such as garlic mustard, are more visible in spring, many invasives are at their peak in August and September, and some, such as multiflora roses, are easiest to spot and remove early or late winter when leaves have dropped.
Although the list of invasives varies from state to state, among the non-aquatics a few thugs appear on nearly all lists: Norway Maple (Acer platanoides), Japanese Knotweed (Polygonum cuspidatum), Oriental Bittersweet (Celastrus orbiculatus), Black Swallowwort (Vincetoxicum nigrum), Goutweed (Aegopodium podegraria), Purple Loosestrife, Japanese Barberry (Berberis thunbergii), Honeysuckles (Lonicera, five types), Autumn Olive (Elaeagnus umbellata), Common and Glossy Buckthorns (Rhamnus cathartica and R. frangula), and Multiflora Rose (Rosa multiflora).
As with serious human diseases, the best, first steps are prevention and early detection. Pulling up small shoots is annoying, but easy work compared to hacking through a thicket of multiflora roses with a chainsaw.
Purchasing and using native plants helps lessen market pressure on nurseries to carry invasives. Integrated pest management (IPM) should always be attempted first. Mechanical control is an option when the invasion is small, when other methods are environmentally risky, and when the plants can be pulled from the ground or water without disturbing other vegetation. A weed wrench can be effective in removing shrubs and small trees invading woodlands. Repeated defoliation of some perennial invasives can weaken them to the point of failure. Controlled use of herbicides may be an appropriate choice for larger, heavily infested areas.
At the very least, cutting invasives to the ground will reduce the number of viable seeds released. Several of the resources listed below this article offer management guidelines that include IPM and have been reviewed by university extension services.
Whenever you remove invasives, remember to plant a native or appropriate replacement—newly opened patches of soil are happy hunting grounds for the next generation of space invaders!
Online Resources and References
(Functional as of August 18, 2003)
U.S. government gateway resource site on invasives, extensive list of links
University of California/Davis
Research and management news on invasives
The Nature Conservancy
News and useful links
nature.org/initiatives/invasivespecies.
New England Wild Flower Society
Massachusetts invasives list, survey information, IPANE information and data
www.newfs.org/conserve/index.htm
Provided by the Western
Massachusetts Master Gardener Association
www.wmassmastergardeners.org.