ID Tip: When Invasive Shrubs Show Themselves

By Martha Gruelle|November 8, 2013

If your site is in or near an urban area, chances are your natural spaces are impacted by invasive plants – species that evolved in distant ecosystems and now threaten to take over. (See below for why this matters.)

Finding and removing these plants before they get out of hand is a great investment – an ounce of prevention that will save many hours of “cure.” But if you’re not a plant person, how can you identify an invasive shrub?

First there are some great guides on line. Michigan Natural Features Inventory, for instance has fact sheets and field guides (as well as best control practice guides).  Ontario’s Invading Species Awareness Program offers a Quick Reference Guide to Invasive Plant Species, as well as information on aquatic and other invaders. Your local nature center, park staff, or other naturalist can probably confirm your identification if you think you’ve spotted an invader.

Green Is Not a Fall Color

Second, right now in the fall, invasive shrubs are showing themselves! They stay green after leaves of native shrubs and trees have started to senesce (turn to autumn colors and die).  If you look through your woodland and see a few (or many) green shrubs in November, check’em out.  They’re likely one of our most common shrub invaders: common buckthorn (Rhamnus cathartica), glossy buckthorn (Frangula alnus/Rhamnus frangula), bush honeysuckle (Lonicera spp.), or autumn olive (Elaeagnus umbellata).

Invasive-Shrubs-HE-NewsletterA great way to become very familiar with invasive shrubs is to volunteer with one of the groups that regularly removes them. Michigan DNR State Parks Stewardship Program, local parks, and land conservancies often request volunteers for this labor-intensive work. After a few hours up-close-and-personal with an invasive shrub, you will know its characteristics pretty well. Michiganders can consult the on-line calendar for volunteer opportunities.

Now is a good time for controlling invasive shrubs, too. The most commonly used control method is cutting near the ground and then treating the stump with herbicide to prevent re-growth. Fall and winter are good times for this treatment; you do not want to be doing this in the spring and early summer when the sap is rising, slowing absorption of the herbicide.

In Ontario, the Cosmetic Pesticide Ban allows use of herbicides to manage natural resources, including to control invasive plants, if you request and receive an exemption from your local Ministry of Natural Resources office. You will probably need to hire a licensed exterminator. In Michigan, one does not need a certification to apply a “general use” pesticide (ie, one that can be purchased at a garden center), unless you are doing so commercially or as part of employment. If you do involve a (licensed or registered) commercial applicator, they can efficiently spend their time treating stumps that your volunteers have cut.

“What’s So Bad about Buckthorn?”

You have probably heard from WHC before about why conservationists target invasive plants, but just in case: invasive species are one of the top two reasons for species extinctions around the world. Invasive plants degrade habitats by crowding out the native plants—hundreds of species of plants replaced by one. Native plants are the basis of the food web: insects are evolved to feed on certain plants, with higher animals depending on those insects, and on up.

Yes, birds and other wildlife do consume the fruits from some non-native, invasive plants, and not necessarily to their detriment (although one invader, common buckthorn, causes a laxative effect which is unhealthy for migrating birds). But while late summer and fall fruits of invasive shrubs may be nutritious, next spring will be a different story. In the spring, migrating birds need insects to fuel their long trips since few plants are in fruit, and nesting birds need protein sources (yum, yum, caterpillars!) to produce eggs and feed growing chicks. Non-native shrubs host many fewer insects, so much less forage for birds.

So watch for green shrubs in late Fall, see if they match descriptions of common invaders, and if so, plan to act as soon as practical.

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