Herbicide Control for Canada Thistle in CRP

As we mentioned in a recent post, one of the first steps in weed control for CRP is to identify the weeds you are dealing with. Like any plant, weeds have different life cycles and seeding methods. They are resilient to some chemicals and weak to others. Once you’ve identified the weeds appearing on your CRP land, you can create an herbicide program to effectively control them. 

While there are many weeds that appear in CRP fields, one of the most prevalent (and difficult) is Cirsium arvense, commonly known as Canada thistle. Other names for this noxious perennial include creeping thistle, field thistle, cursed thistle, and even lettuce from hell thistle.  

Despite being called Canada thistle, it doesn’t actually originate from Canada and can be found across the world. Regardless, it’s important that it’s dealt with quickly and aggressively. Left unchecked, this weed can run rampant across your land. 

Creating an Herbicide Plan for Canada Thistle 

Canada thistle is especially tricky in part because it spreads through both seeds and root shoots. Combatting it requires multiple herbicide applications throughout the year. The exact dates can vary depending on your location, weather, and more.  

The first application period is typically between March and May when the thistle’s rosettes appear. While it won’t do much to the root systems, it should kill the above ground plants without damaging your CRP vegetation too much provided the CRP vegetation hasn’t started growing yet. Herbicides containing clopyralid, aminopyralid, or glyphosate typically work best. 

The next period happens between mid-May and mid-June right before flowering begins. Another application of clopyralid, aminopyralid, or glyphosate can help keep the thistle from seeding and spreading further. Spot mowing can help with population control as well, though it won’t actually kill the weed.  Application during this time should be done as spot treatment as CRP plants will be active and growing at this point. 

The final application period takes place between September and October. This is when you’ll target the root systems directly, reducing the presence of the weed the following year. You’ll want to make sure this is done before the ground freezes.  Waiting until the CRP vegetation has gone dormant is very important.  If you broadcast spray too soon you will damage or kill the CRP vegetation you are trying to protect. 

In addition to these phases, regular spot checking and treatment should be done throughout the year to prevent sudden outbreaks. Even after multiple years of herbicide application, Canada thistle may not be completely wiped out. 

This is why it’s very important that you buy quality CRP seed with high germination rate that has been tested for noxious weeds. While it won’t keep all weeds out of your CRP establishment, it will reduce their presence while providing native vegetation that is more resilient.  

You can browse our exclusive CRP seed mixes here. We can also provide a quote for seed mixes developed by NRCS here. If you need any assistance, don’t hesitate to contact us at 888-224-2004 or quote@allnativeseed.com.