Invasive Species Control Needs to Start Early

By Joe Wiley, IF&W Wildlife Biologist

Invasive plants can affect the enjoyment and use of your land – in mostly negative ways. The key to controlling invasives is to first identify them. In some cases, there are native species in the same family as invasives, so knowledge is important when it comes to identification. There are many identification guides available to assist, and several are listed here.

What is an invasive species? It’s an exotic (non-native) species that rapidly spreads into indigenous habitats, negatively affecting native plant communities or the production of crops. You should really be concerned with any invasive plants on your land, because they all affect how you and wildlife use it. Invasive species can threaten biodiversity by reducing native plants or changing ecosystem processes. They can also impact the forest regeneration you’re planning for the future of your forest.

Some common woodland invasives to look for are Asiatic bittersweet, Japanese barberry (both glossy and common), buckthorn, honeysuckles, Norway maple, autumn olive and multiflora rose. Early detection and rapid response is the mantra of invasive control experts. Identify the threat and eliminate it before it becomes overwhelming.

Most invasive plants leaf out earlier than native trees and shrubs. On my 26-acre woodlot, I find that April is the best time to monitor for invasives. I walk transects across the woodlot in the spring to monitor invasives and check for winter tree damage. If I see something green in the understory, it’s usually multiflora rose, Japanese barberry or one of the many non-native honeysuckles. These plants are easy to pull out of the ground when small and seldom sprout from any root fragments left in the soil. I usually put a wire flag where I’ve pulled out an invasive plant to check for re-sprouting in July or August.

If the invasive plants are too big to pull by hand, the best control method is a spot treatment using herbicide. Contract with a Maine licensed applicator or do it yourself if you have the knowledge. Caution: A license is required to apply herbicide to any land other than your own. Check with the Maine Board of Pesticide Control, 287-2731 or www.thinkfirstspraylast.org if you plan any herbicide applications. 

Foliar herbicide applications in mid-August are effective for most invasives. On my land I prefer to use herbicides that have no residual soil activity, such as glyphosate or triclopyr for foliar applications. My preferred control method is a basal bark application using triclopyr and bark oil. This comes premixed as Pathfinder II or you can mix it yourself. The neat thing about this method is that it’s effective whether plants are actively growing or dormant. The base of the plant must be dry and you can’t use this method when there’s snow on the ground. Its big advantage is that it minimizes the amount of chemical used and you only apply it to the target invasive once.

Your management activities can also increase the risk of invasive species. Anytime you disturb soil or provide more sunlight to the forest floor you create ideal conditions for non-native plants. Were there invasives in the harvest area that went unnoticed? Where did that logger’s harvesting equipment come from? Were there seeds on the equipment? What about seeds in mulch hay?

Purple Loosestrife

I use these examples because I’m guilty of at least two of them. I got purple loosestrife on my woodlot from mulch hay I used and I was involved in a pine harvest where the understory was dominated by small honeysuckle shrubs which went unnoticed during marking. The honeysuckle responded vigorously to the increased sunlight the season after the harvest and required control.

Further information:

Maine Natural Areas Program, www.maine.gov/doc/nrimc/mnap/features/invsheets.htm

Invasive Plant Atlas of New England, online at www.ipane.org

Invasive Plants Field and Reference Guide, 88-page USDA Forest Service guide with color pictures of 15 invasives at: www.fs.fed.us/r9/wildlife/nnis/invasive-species-field-guide.pdf