Over the past 20 years, we have seen more and more cocklebur becoming established on our farms and many farmers in the area have noted that as well. On Chris’ farm, I think it started when I fed whole shelled corn to my cattle out in the pastures to extend hay supplies in the winter. You would think this summer annual would be easy to control, but it is a challenge.
We recently finished a 5-year trial on timed mowing of pastures in the summer. A year after concluding the study, we went out to the site in September. It had not been mowed yet, and it was completely engulfed with cocklebur. No matter when or how often we mowed, after doing the same thing for five years, there was no difference.
One would think that if we went out and mowed a summer annual when the stem is elongating with immature seeds and cut below the seeds, we would kill the plant, and that still may be the case. However, how about the 10% that were too short to mow or still immature? During the trial, we noticed many cocklebur plants maturing only four inches tall with lots of seeds after mowing — very discouraging. Even then, we wondered why it kept spreading so much.
According to “Weeds of the Northeast” 1997 (and trying not to get too deep in the “weeds”) this plant blooms July through September, it has male and female flowers on the plant, and each bur (the seed cover we have to pull off of our dogs) contains two fruit, each with one seed. The discouraging part here is that the lower seed can germinate soon after the bur (or seed pod) splits open. The other seed can remain dormant for one to several years, meaning it may take years to eliminate.
Timely, repeated mowings may keep cocklebur in check or slow the spread, but if it becomes established, pastures will likely need herbicide applications. According to the 2022 OSU Extension Weed Control Guide, most broadleaf herbicides for pastures are very effective, as well as glyphosate for spot treatments. Before selecting one, consider the residual impact of the herbicide and how long one must keep animals out of the pasture after spraying. We are fortunate that there are options for short-term and long-term residual of the herbicides, and there are herbicides that may have short to no grazing restrictions depending on the class and type of livestock you have. As always, read and understand the herbicide label and restrictions before using, some have very strict grazing and haying requirements.
If you have pastures where cocklebur is becoming a serious problem, it will only get worse, so consider taking action. If you have some fields where you find a few rogue plants, consider pulling them out before they can get established. One plant today could become many next year.