Feb 27, 2017

Where to Start with Controlling Invasive Plants

By: Lawanda Jungwirth

We all want to do what’s best for our environment in order to support a healthy ecosystem so that the animals we love to hunt and fish will thrive.  Controlling invasive plants is an important part of that.  An invasive plant is one that causes economic or environmental harm, or harm to human health.  They destroy or degrade wildlife habitat and food sources, increase runoff through soil instability, reduce water quantity and quality and lower property values.  

A mixed hardwood forest may support hundreds or even thousands more species than woods overrun by buckthorn or garlic mustard.   And it has zero timber value.  A lake clogged with Eurasian water milfoil has fewer fish that boats can’t get to anyway through all the weeds.

How do you know if your property has invasive plants, and if you find them, what should you do?  There are some clues as to whether a plant is invasive.  Is there a lot of it?  Have you noticed it spreading over time?  Is there only one kind of plant growing in a certain area so that a mix of other plants is missing?  Does it leaf out earlier, or remain green later, than most other plants?  If you are familiar with the property, have you spotted something new that you’ve never seen before, maybe something that doesn’t seem like it should be growing there?  

Before rushing to eliminate what you think is an invasive, be sure to make a definite identification of the plant.  The reason for this is that you don’t want to accidentally eradicate healthy native plants that are making a positive contribution to the ecosystem.  Also why waste time or money getting rid of plants that aren’t doing any harm?

To help with invasive plant identification, the Wisconsin DNR provides fact sheets and photos of 116 terrestrial invasive plants and 16 aquatic invasives here:  http://dnr.wi.gov/topic/Invasives/.  More photos can be found at the website of the Invasive Plants Association of Wisconsin:  www.ipaw.org.  The book Invasive Plants of the Upper Midwest, by Elizabeth Czarapata, is also an excellent resource.  Although published over ten years ago, the photos are good and the information is still relevant.  Some of the chemicals used for control may have changed or been outlawed, but once the plant is positively identified, you can refer to the DNR website for current chemical control information. 

There are many ways in which invasive plants are controlled:  manual/mechanical, which includes cutting, pulling, mowing, grazing and burning; chemical (herbicides); and biological, a natural control method using introduced insects, disease or fungi.

Another reason that properly identifying the invasive plant is important is that each one is particular as to the most effective control method or the best time of year to implement a control.  For example, it doesn’t pay to go whacking away at buckthorn without an immediate chemical herbicide follow-up because cutting will stimulate re-growth and make the problem ten times worse.  Likewise, it doesn’t make sense to pull garlic mustard in mid-summer after it’s already produced and spread its seeds.  

Just like non-invasive plants, invasives may be herbaceous (those that die back to the ground in winter) or woody (trees, shrubs or vines).  

The goal for controlling herbaceous invasive plants is to prevent them from setting seed.  Some herbaceous plants can be cut or mowed just before they set seed.  However, that doesn’t always work because some invasives will resprout and set more seed the same year.  Sometimes even if the plant has just begun to flower, the cut off part of the plant continues to mature and set seed even after being separated from the roots.  In that case, the cut parts must be collected and burned or landfilled. 

Many herbaceous plants can be pulled or dug.  Garlic mustard and dame’s rocket are two of them.   Every control method has its downside though.  Pulling plants disturbs the soil, bringing new weed seeds to the surface that will germinate.   Ideally, native plants would be planted in the newly bare soil.  Uprooted plants should be burned or landfilled.

Herbicides may be effective on herbaceous plants, but herbicides don’t distinguish between bad plants and good ones and you risk killing plants valuable to the ecosystem.

Control of woody invasive plants usually involves a bit more muscle or bigger toys than control of herbaceous plants.  In a large infestation, remove the plants producing seeds or berries first.  Then go after the youngest, smallest ones that can easily be pulled out of the ground by hand after a good rain.  Mid-sized plants can be pulled with the use of a weed wrench.  

Chemical herbicides are often used for control of woody invasives.  Some are applied to the foliage, some to the cut stump and others are injected.  Refer to the DNR website mentioned above for the exact herbicide, most effective method, and best time of year for each particular plant.  Always heed cautions on herbicide labels and follow instructions exactly.

Biological controls have been used successfully on many invasive plants.  It takes many, many years of study before a particular biological control becomes available for general use.  Scientists want to be absolutely certain that the insect, disease or fungi won’t have an adverse effect on native plants or agricultural crops before they unleash it on the environment.  There have been some failures in that area along with the successes; thus, the extreme caution.  Biological controls are not something you can buy at the store.  Usually they are available through a university or DNR program.  

  Always remember that you have to go back the next month and the next year and the next year after that to check areas where invasives have been controlled.  Some invasive plant seeds are viable for decades and may have taken the opportunity to germinate.  Or birds or wildlife may have brought new seeds in.  You already know the spot is ideal for invasives to flourish, so those bad seeds have a pretty good chance of prospering there.  Persist!


  1. Identify the invasive plant.
  2. Learn the various control methods.
  3. Choose a control method you are comfortable with, taking into consideration your time, budget and physical capabilities.
  4. Implement the control and check the area regularly for missed plants and new growth.


Work from the least infested area toward the worst; in other words, from the outside in.  The exception is if there is a high quality natural area on the property; then start there to protect that area and work outward.