The Weed Experiment Part 1 of 2

Weed management is always on the minds of local ranchers. Frequently I am asked about weed control and there is no standard answer. Variables like weather, grazing practices, soil fertility and mechanical weed management makes giving a definitive answer impossible.

I use a five foot mower (shredder) as a counter weight when carrying things in the bucket of my front end loader. So, I often mow a patch of weeds on the return trip to the barn where I store the tractor. Over the years, I have observed the rate at which the weeds return. One year, a single swarth of the mower removed the weeds and they did not return in that location until the following year. It got me to thinking what caused this to happen. Was it the species of weed mowed? Was it the way I grazed the pasture following the event? Was it the weather?

During the 2024 and 2025 growing seasons, I decided to try weed management in one pasture based on mowing practices only. As many ranchers do, I experiment with weed management using grazing methods, soil supplements and mechanical methods to reduce weed pressure. I never use toxic chemicals. The following are my observations, and as the commercials state, “Your results may vary.” This experiment has been many years in the making.

The experimental pasture is a nine acre rectangle. I have the pasture divided down the center with a few posts where I have intentions of installing electric fence. The pasture is fairly uniform with Bermudagrass and Bahia grass mix. In the spring the pasture has some clover and winter grasses throughout the area, but the Bahia grass reduces the amount of winter grass and clover mix.

Fall rains usually provide the moisture needed for early growth of winter grass mix prior to any freezing weather. The winter grass mix is rescue, rye and ryegrasses. I try to stockpile summer grasses for winter grazing but rely on the winter mix for green forage grazing during the coldest months.

Fall rains are critical for stockpiling and winter grazing. Without them, winter grasses do not germinate or grow. Droughts in our area typically start in November. Little or no rain in this month can be an indicator of a dry summer coming, no matter how much rain falls in the spring. I am 77 years old, but I don’t remember many years when November was dry. So, when the fall months of 2024 and 2025 were dry, beginning in September after a dry summer, I got to see what weed management would look like after mowing practices were in place.

I decided to mow a single strip of weeds every other week from mid-April to August. I would monitor the number and type of weeds. I typically avoid mowing weeds in August because, as I have found, this leaves a bare spot in the pasture. Grasses and weeds do not like mowing with little water available for regrowth.

All grasses and weeds were mowed at four inches on the pass to the end of the pasture and six inches on the return pass. This meant that some weeds that were higher than the grass to start were cut even with the tops of the grass cut. Weeds that were lower than the tops of the grass had to compete with the grass for sunlight to grow. Variable mowing heights meant that some grasses and weeds were cut, and sometimes only tall weeds were cut.

My main weeds are western ragweed and dove weed. There are two species of dove weed present. These are the two weeds that cattle tend to avoid. Western ragweed is occasionally eaten, but dove weed is avoided. Western ragweed spreads by seed and rhizome, while dove weed spreads by seed. Dove weed is an annual, while ragweed is a perennial.

One half of the pasture was used for the experiment in the months of April to mid-June, while the other half was used as a control: no mowing. I began on the outside and mowed inward toward the control area.

Results: The areas mowed in April to mid-June showed some signs of weed control for dove weed, but more control for Western ragweed. I thought this strange, but it seemed that the competition from Bermudagrass and Bahia grass seemed to crowd out the Western ragweed. This was not full control, but it did suppress the weed enough that cattle seemed to graze it more while eating the other grasses and forbs.

Areas mowed from late June to August showed almost no effect on Western ragweed growth, although growth did slow due to less rainfall and higher temperatures. Ragweed spread less in Bahia grass than in Bermudagrass. The thicker growth habit of Bahia grass competes well with all weeds.

In all areas, the dove weed was suppressed by Bahia grass. Fewer dove weed seemed to germinate in thick patches of Bahia grass no matter the time of the year. But dove weed germination was unaffected in Bermudagrass areas. I have a pasture of Jiggs Bermudagrass for comparison. Even the thicker growth of Jiggs compared to common Bermudagrass did not seem to greatly deter germination of dove weed.

While you may or may not find this experiment interesting, please read Part 2 of this article in an upcoming issue of the Fayette County Record. I think you will be surprised with what I have to report.

David E. Will is a local rancher and consultant. He can be reached at (830) 629-9876.