Thistles can be a real problem in pastures and the wet weather much of the state has experienced lately could be setting you up for a bumper crop next spring, especially if you’ve had them in the past. So, start looking now in areas where you’ve had thistles before.
Below are several examples of different thistle species in the rosette‐stage. Late January or early February is typically a good time to apply herbicide. Treating during this time gives more of the seeds a chance to germinate and you can still treat them before bolting occurs.
Thistles are easily controlled with just about any herbicide if they are treated in the rosette stage before the stems start to “bolt” or elongate. A rosette is a circular arrangement of leaves, with all the leaves at a similar height. At this stage, lower herbicide rates can be used. Individual plant treatments (IPT) are very effective for spot-spraying. Make sure to use a good commercial surfactant which is nonionic and has 80 or 90% or more active ingredients. Methylated seed oils (MSO) can also be used as a surfactant. Check MSO labels for the correct per concentration.
For more information on specific chemicals labeled for high thistle kill contact Chelsea Dorward at the Bosque County Extension Office, 254-435-2331 or Chelsea.firstname.lastname@example.org.