Canada Thistle Control Recommendations

Canada thistle is a perennial that reproduces from seed and by an extensive root system. It is dioecious with the male and female flowers on separate plants. For viable seed to be produced, both male and female plants need to be present. The number of seed produced per head will vary from 1 to 100, with a large plant being capable of producing 5,000 seeds.

Root system
The root system of Canada thistle allows the plant to spread rapidly once it has become established in an area. Nearly all parts of the roots can produce buds which gradually develop into shoots that grow and form new plants. Root segments as small as 1 inch can produce new shoots. Canada thistle seedlings that have four true leaves and are 20 to 30 days old can regenerate by their root system. Tillage equipment operated through Canada thistle can easily spread pieces of roots to non-infested areas and result in new infestations.

Timing of chemical control
The two most effective times for herbicide application to Canada thistle are at the bud stage and during re-growth in the fall. Results from experiments conducted in western Nebraska indicate that herbicides applied in September have generally provided 15 to 20% more Canada thistle control than herbicides applied in June.

Herbicides
Herbicides such as Ally/Escort, Amber, Banvel, Curtail, Glean/Telar, Roundup, Stinger, and Tordon have all been successfully used for Canada thistle control

Persistence is the key to a successful Canada thistle control program. You must use multiple herbicide treatments to achieve control. Choose control measures that can be used for at least two to three successive years. Thoroughly plan your control program in advance and adhere to it until control is complete. Some examples of possible control schemes are as follows:

1. Control in Corn. Apply atrazine preemergence to corn growth; follow up with Banvel, Marksman, or Stinger postemergence before corn is 24 inches tall. Treat Canada thistle again in the fall of the year with Banvel, Curtail, Roundup, or Stinger. Follow this program for two or three years.
2. Control in Pasture. Apply Banvel, Curtail, or Tordon in the spring of the year when Canada thistle is about 10 to 20 inches tall. Follow up with another treatment in the fall if active Canada thistle growth is evident. Follow this program for two to three years.
3. Control in Winter Wheat. Apply Ally, Amber, or Curtail in the spring to growing wheat before it reaches the boot stage of growth. Treat Canada thistle again after wheat harvest in the fall with either Banvel, Curtail, or Roundup. Follow this program for two to three years.
4. Control Near Water. Apply Rodeo plus surfactant in the spring and again in the fall. Follow this program for two to three years.
5. Control in Lawns and Residential Areas. Apply a broadleaf weed killer which includes 2,4-D and Dicamba in the spring and fall. Use labeled rates. Some products available include Trimec, Super-Weed-No-More, and K-Gro Broadleaf Weed Killer. Confront is an effective product, but only available in larger quantities. For control in and around trees and shrubs, apply a glyphosate product such as Roundup only to active growing plants in spring and fall, taking care not to get chemical on desired plant.