ENID, Okla. —
For the last three years, I have received a phone call from the same two individuals wanting to control musk thistle in May.
Each of those years and to each individual, I have discussed the limits of our success with trying to control musk thistle in the spring time. In our discussion, I always refer to our control options in the fall being better than in the spring and our options for products to control musk thistle being much broader. For those two individuals and other wanting to control musk thistle in the spring, please read this article.
Last week when the wind was much calmer than at the end of week, I got the chance to walk several wheat fields and evaluate the crop status. While out of the office, I got to look at several sites that to my surprise had more musk thistle than what I wanted to see. My first thought was that we had been too dry for musk thistle to get that much growth. Some of the rosettes were 6 inches or better in size.
There should not be a way that these could have gotten enough rain to have that kind of size. I then had to remember that musk thistle is considered in most weed book to be a bi-annual, which means it will spend two growing seasons in the rosette stage and then bolt to producer seeds in the second year of its life. The growth I was looking at last week were plants that had germinated last fall when moisture conditions were much more favorable than this summer and fall. Again, you have to understand the growth cycle of the weeds that are causing you problems to gain better understanding of how to control them.
Musk thistle is much easier to control in the rosette stage than when they have a seed stalk that you have to contend with. Herbicides that work well when musk thistle is in the rosette stage include 2,4-D, Grazon Next, Grazon P+D. Ally, Cimarron Max and a combination of 2,4-D and Banvel. The best time to utilize these products would be in the month of November when moisture conditions are favorable and the daytime temperatures exceed 60 degrees.
The before-mentioned herbicides used during the fall time frame have much less affect on other plants that may be much more susceptible to these herbicides in the spring it they go off target. For example, if you were to use these products in the spring time, you would have to be careful of crops like soybean or alfalfa and peppers and tomatoes in gardens near your spray locations. This scenario also holds true for landscape plants like oak trees, redbuds and pink velour crape myrtles.
Your Oklahoma Cooperative Extension Service ag educator will be able to address your questions concerning control options and timing of applications for the musk thistle problems that you are facing. If you do not have time this fall for the ideal spray time, the spring time applications can be made, but if the musk thistle gets a seed stalk on it, I will remind you of this article next spring and ask you why the fall or early spring time applications were not utilize.
Gribble is Oklahoma Cooperative Extension Service northwest area agronomist.