When and How to Treat Invasives

Best Control Practices 

Garlic Mustard

Hand removal of entire root system of plant is practical for light infestations.  For larger infestations, cut stems at ground level or within several inches of the ground to prevent seed production.

Herbicide, such as Roundup, may be applied for very heavy infestations.  Fire can be used but can encourage germination of stored seeds and promote growth of emerging garlic mustard seedlings.

Canada Thistle

Repeated mowing or selective cutting close to the ground can reduce infestations with 3-4 years.  Cutting should be done at least three times per year.  Mowing should be done before flowering or it will help spread seed. 

Japanese Knotweed 

We recommend not treating Japanese knotweed until late August/early September when the plant is in the flowering stage.  The most effective herbicide to use is Habitat or Clearcast….both are slow acting systemic herbicides that will prohibit the plant from producing life sustaining sugars the following growing season.  The entire plant doesn’t have to be treated, just the active growing tips. 

Do not cut earlier in the year to reduce the vegetation height or attempt to treat with Glyphosate (Round-Up) since both practices have shown that they cause the plant to spread faster.  You will have to follow-up with another spot treatment the following year….only the stand will be much smaller.  Always have a plan in mind for a temporary cover crop that will fill in the void the knotweed created…..garlic mustard/thistle will usually move in to fill the vacancy.

If homeowners have to cut the plant for whatever reason, the litter must be bagged properly and disposed of in a landfill or burned.  Pieces of the plant, when in contact with the ground, will re-root and start new populations.  Disposing of the material improperly is the main cause for starting new populations in the state.

For a complete look at treating Japanese knotweed, read the "Japanese knotweed - Best Control Practices" published by the Michigan Department of Natural Resources and the Michigan Natural Features Inventory.