Those underground rhizomes! There is as much living material underground as above.
A perennial weed with a super strong root system, Canada thistle does not emerge in time for a pre-seed burnoff. If allowed to mature, it is instantly recognizable with its spiny rosette and trademark purple flowers. It grows in dense patches with many plants sharing the same root system.
HOW TO DEFEAT THIS VILLAIN
Canola - Use a high registered rate of herbicide (especially in Roundup Ready® canola) and you will get season-long control with enough regrowth to get them in fall.
Cereals - You have two options: 1. Burn off the top of the weeds in-crop, or; 2. Use recommended products in-crop for season-long control, allowing for enough regrowth in the fall that the plants will take up a post-harvest herbicide application.
Peas & Lentils - Choose a field with little to no Canada thistle because there's no hope of controlling in-crop.
A high rate of Liberty® (1.6 L) or a two-pass strategy in canola will burn off the top. *Pro Tip: a water rate of 12-15 gallons will take Liberty's control to the next level.
- In Roundup Ready canola, a two-pass strategy with Roundup Transorb® at 0.33 L (twice), then a 1.5 L rate post-harvest is your best bet for control.
Cirpreme® will control Canada thistle in-crop.
While it does add cost to your weed control regime, the one-two punch of herbicide application to burn off the top of Canada thistle followed up with a post-harvest application of Roundup Transorb at 1.5 L/ac is your best bet for control.
It’s best to control Canada thistle in the fall, when the plant is moving sugars down to the roots. It will move herbicide to the roots as well. These weeds are tough and can be expensive to control as they require a weakening application in-crop and a second application to fully control them.
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