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Has your property been “invaded”?

Posted: September 19, 2012

Drive down any road and you will probably find non-native plant species beginning to invade our forests, stream corridors, meadows, and yes, even the landscape at your home. When was the last time you walked your property and wondered why there seems to be plants that are taking over?
"Garlic mustard has been shown to be toxic to the West Virginia white butterfly."

"Garlic mustard has been shown to be toxic to the West Virginia white butterfly."

Your property may already have been invaded by an “exotic invasive” plant or you might have even accidentally planted some in your landscape that will soon escape and invade a nearby forest or stream.  As good stewards we need to become more aware of the impact these non-native invasive species have on our local environment and learn to identify and properly control these species before they completely take over an area.

What is an “Exotic Invasive Plant”?
It is really just another name for a weed that was introduced from other continents and has escaped cultivation causing serious harm to native habitats for insects and wildlife.  Before you start tearing out all your landscape plants, you must know that NOT all non-native plants are invasive and there are some native plants that have a tendency to become invasive (especially on disturbed sites).  In order for a plant to be considered “invasive”, it usually grows aggressively (on various sites and growing conditions), spreads quickly (by seed, rhizomes, or cuttings), lacks natural predators, pathogens and parasites, and displaces native plants.

Does it really matter what is growing on my property?
Researchers at Cornell University and elsewhere have estimated that “Exotic Invasive Species” (plants, insects, and animals) are costing the United States more than $138 billion each year, due to their economic impact on agriculture, forestry, fisheries, wildlife, ornamental landscapes, and waterways.  The costs and losses associated with weeds are estimated at $80 billion per year.

Garlic mustard has been shown to be toxic to the West Virginia white butterfly, a rare species that lays eggs on native toothwort (Dentaria sp.) which is being displaced in forests by garlic mustard.  When eggs are laid on garlic mustard, fewer eggs hatch and larvae don’t mature due to the toxicity of the plant.

Locally Japanese Knotweed is taking over many stream and river banks, displacing native woody vegetation.  Once established, these dense bamboo thickets shade out and prevent the growth of young trees and shrubs that help hold the soil in place and prevent sediment from entering the water during flood events.  Changes in the vegetation of our riparian areas has indirect impacts on aquatic habitat and fish populations as shade is lost and dissolved oxygen levels drop.  The aquatic food chain is also affected as some species of macro-invertebrates (stoneflies, mayflies, or caddisflies) need native flowering trees in the riparian area in order to complete there lifecycle.

So What Can Be Done to Prevent and Control “Exotic Invasives”?

•    Become Educated and learn what invasive species look like.  Contact your local Penn State Cooperative Extension office in your county and request information (fact sheets) about specific invasive species or bring them plant samples for identification.


•    Don’t plant species that are considered invasives:  Get a copy of DCNR’s Invasive Species brochure that lists plants that should not be planted.


•    Discover alternatives in your landscape:  Promote responsible gardening by learning about the native plants around you.  Buy nursery propagated  native plant material.  Never dig or buy plants that have been dug in the wild.  


•    Remove invasive exotics:  Remove from your landscape and replace them with native plants or non-invasive exotics.  In order to properly control many invasive plants, some herbicide use is required.  For some, pulling or cutting only spread them more.  The impact of leaving an exotic invasive to take over a site far outways the use of herbicides to remove it. 

Websites to visit for more information about identifying and controlling Exotic Invasive Plants
http://extension.psu.edu/private-forests/tools-resources/publications/invasive-plants-and-insects-Penn State School of Forest Resources Invasive Factsheets
http://plantscience.psu.edu/research/projects/vegetative-management/publications - Penn State University Roadside Research on Invasive Plants
http://www.invasiveplants.net/ - BioControl of Non-Indigenous Plant Species
http://www.dcnr.state.pa.us/forestry/plants/index.htm  - DCNR Invasive Plants

By Vincent Cotrone, Regional Urban Forester,
Penn State Cooperative Extension