Managing Herbaceous Invasives

Managing herbaceous invasives and managing woody invasives are where most of our management time and resources are spent. When saying this, collecting, cleaning, and overseeding are included as they as critical components of this management.

There are 3 main methods for managing invasives:

  1. Mechanical
  2. Chemical
  3. Overseeding

3 Mechanical Methods

  1. Parsnip Predator
  2. Hand pulling
  3. Mowing or brushcutting

Parsnip predator — This tool gets a work out here!

Parsnip predator

Mowing or Brushcutting 

This techniques will not kill the plants unless they are biennials that are in bloom (e.g. wild parsnip, Pastinaca sativa). If you are short on time or other resources, mowing and brushcutting can be used as triage techniques. This means it could keep the perennial plant from setting seeds; it does not kill them. Some have the ability to rebloom on a shorter stem. It keeps the invasives’ seedbank from increasing, which is important.

 

Chemical Methods – Using Herbicides

Know your herbicides before you use them. Here is a document that explains how to analyze herbicides. Especially important is the half life in the soil. This tells you how long a certain amount of the herbicide will be reduced by half in the soil. The less time this is, the fewer opportunities for it to move around and negatively affect other vegetation.

Wear personal protection when spraying and mixing. 

Always read the label. It is a legal document. Should something “happen” while you’re herbiciding, you are legally liable for any misapplications if you did not follow the instructions on the label.

3 of the Techniques shown here work well for herbaceous invasives.

Additional herbicide information worthy of reading!

Overseeding

Overseeding on a regular basis is a smart practice but must be used in conjunction with mechanical and chemical to be effective. The goal is for the native plants to outcompete the invasives. Patience is required and repeated overseeding is necessary.  Overseeding cannot be used as the sole means of herbaceous invasive control.

 Overseeding isn’t as intensive as planting the prairie originally, but you’ll find info about seed mixes and seed rates and other ideas that could be helpful to you.

What About Using Fire?

In general, fire doesn’t control herbaceous invasives. It tends to increase them because as fire does its job of removing the thatch, it opens the land and all seeds germinate. Invasives seem to have an advantage, especially if they ones that grow early in the season. It’s stated that burning late in the season will set back some of the early growing ones, but biological proof of that hasn’t been found and there will be collateral damage. Burning late will have the same deleterious effect on your native plants and risk harming your herptiles. If fire is part of your plan for other reasons, follow up is required; plan and budget for it. 

Fire can be effective on controlling invasives, such as on garlic mustard. This is because they green up before the native plants, which means burning doesn’t create collateral damage.

We have allowed alien plants to replace natives all over the country. Our native animals and plants cannot adapt to this gross and completely unnatural manipulation of their environment in time to negate the consequences. Their only hope for a sustainable future is for us to intervene to right the wrongs that we have perpetrated.

Douglas W. Tallamy

Know Thy Enemy

The best way to know how to manage an invasive is to learn about its growth habit and biology. This prevents costly mistakes from “loud confident” voices that may not have the best management suggestion. Minnesota Wildflowers

The best info I’ve found is

  1. Minnesota Wildflowers has detailed info on native plants that can be sorted a multiple of ways.
  2. Wisconsin DNR lists invasive species that are prohibited or regulated.
  3. UW Extension has a list of invasive species with details about each
  4. IPAW (Invasive Plant Association of Wisconsin) offers lots of info.

The Growth Type Can Dictate the Control Method

Biennial plants can be removed by mechanical means.

Pros: it reduces the herbicide put out and your costs

Cons: it’s labor intensive

 

Clonal plants must be killed with herbicides. Clonal growth means that if you disturb the plant with mechanical means, it will  increase its production and spread further.

Perennial plants can be removed via mechanical or chemical. Usually after around June, we use only mechanical means for these. 

 

Seedbanks – If you’re unfamiliar with term, it refers to the seeds from prior years that remain viable in the soil. Different seeds have different viability lengths, but most are in the upper single digits or double digits. 

It’s important once you begin restoration work that you reduce this seedbank by not letting the invasives go to seed. When time gets away from you, triage is your answer! 

Combining Techniques Provides the Best Outcome

Here is a simple sample management plan (say that three times fast!)

When dealing with individual plants randomly located in your ecosystem:

If mowing and/or burning is already scheduled for spring, then foliar spray or spritz rosettes of the invasives in May-ish.

In July, if the invasive is not clonal, you can use a parsnip predator and sever their roots.

Or

If mowing or burning isn’t scheduled, you can still walk the land and foliar spray or spritz rosettes in May-ish, then do mechanical later.

 

Or

If the early spraying/spritzing doesn’t happen you can still to mechanical any time. And if the plant has a fall regrowth, you can plan management activities in August.

 

AND

ALWAYS plan to overseed these areas between Nov and Jan.

 

Other Possible Examples

  1. When dealing with larger patches of invasive forbs, you can mow them when in bloom, then overseed in fall/winter. This will need to be done several years in a row to reduce the patch. This is effective for those aggressive native forbs such as goldenrod.
  2. If the invasive is grass (usually non-native cool season grasses), mowing it when it tillers (early May-ish) will keep it from flowering. If you overseed it with native grasses, this can be done after it’s mowed as they only need 70 degrees to germinate.

It’s not possible to give a formulaic answer to management. It depends on one’s goals, one’s resources, what invasive plant(s) are there, what native ones are there.