P&PDL Picture of the Week for
August 3, 2009

Canada Thistle

Glenn Nice, Weed Diagnostician, Botany & Plant Pathology, Purdue University

There is a lot of Canada thistle out there producing seed this year. In the state of Indiana the “Destruction of Detrimental Plants” law, Indiana Code 15-16-8, requires “a person owning or possessing real estate in Indiana” shall destroy detrimental plants by “cutting or mowing and, if necessary, by plowing, cultivating, or smothering; or using chemicals in the bud stage of growth or earlier, to prevent detrimental plants from maturing on the person’s real estate.”

According to this law, it is the responsibility of the Township Trustee or your County’s weed control boards to implement this law. Very few counties in Indiana have active weed control boards, so in most counties it is up to the Township Trustee. Sorry, you cannot call the police when your neighbor has not done anything with their Canada thistle. If your Township Trustee has reason to believe you have Canada thistle on your property and it is not being managed, the Township Trustee has the authority to inspect your property after giving you 48 hours written notice. If Canada thistle is indeed there and it is not being managed, the Township Trustee can give written notice to manage the Canada thistle. If the land owner does not comply within five days of written notice the Township Trustee can hire an outside service to control the Canada thistle on your property. This outside service can enter your property and apply management techniques complying to the law. The service doing the control is not “liable for damage to crops, livestock, or other property occurring while carrying out the work, except for gross negligence or willful or wanton destruction.” This also includes property owned by the State.

Who pays for this? Unfortunately, in the end you do. The land owner is generally sent a bill for the work, supplies, and $20 per day if the trustee or trustee’s agent has to supervise. If the bill is not paid within 10 days of notice the cost will be put on the property taxes.

If you have Canada thistle it is best to control it. At the very least, you are in compliance with the law if you simply prevent the Canada thistle from flowering by mowing. The optimum time to mow is at bud, or just as it starts to flower. Canada thistle may still produce flowers if mowed too early. Herbicides that have excellent activity on Canada thistle are Stinger, Curtail and Milestone. Always read herbicide labels before buying to assure the product is appropriate for your situation, then follow the label while using.

For more information regarding Indiana’s law concerning plants please see the following article “Noxious and Invasive Weeds and The Weed Laws in Indiana”(pdf file). For more information regarding Canada thistle control see the “Weed Control Guide for Ohio and Indiana”.


Click image to enlarge

Canada thistle

Canada thistle

Canada thisle by roadside

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service