Cows head for fewer weeds
MU study shows investigates cows’ grazing preferences
Keeping pasture in condition in the Midwest is a perennial challenge. And it’s one that often falls low on the priority list for diversified farms. But research from the University of Missouri shows that modest weed management on continuously grazed pasture can pay dividends in forage production and certainly makes a difference from a cow’s perspective. She likes fewer weeds.
That cows prefer grass over weeds may seem like a good dose of common sense. The idea behind a three-year study from University of Missouri Extension weed scientist Dr. Kevin Bradley and graduate student Bryan Sather was to better understand the effects of a mid-grazing-season herbicide application on a herd’s grazing habits.
Bradley and his student used GPS collars on representative cows in several herds to see where they spent time grazing throughout the season. Across three sites in Missouri, the research team split continuously grazed pasture into herbicide-treated and untreated sections. They took care to make sure the topography, water sources and shade availability were as equal as possible in each section. And, before the project started, herd movement was tracked to get a baseline of grazing habits for each pasture.
“In our pasture weed management research, we’ve been slowly working toward this project for the past several years,” said Bradley.
“We’ve done research that explains how weeds impact forage yield and forage quality, but we have never done research that focused specifically on how weeds impact grazing distribution and grazing preference.”
As you can see from the graphic on the opposite page, cows in the study spent significantly more time on the herbicide-treated side of the pasture.
According to Bradley, findings from the study show some change to yield and detectable forage quality difference, but of particular interest is the fact that a cow votes with her feet.
And that’s an important factor to consider for livestock producers who worry about the legume content of pasture being lost to herbicide.
“Based on this research, it’s more important to the cow to be in a weed-free grass environment than it is to be in a weedy environment with legumes,” said Bradley.
He went on to say that often times, the legume population in a pasture is something less to worry about than a weed population that often out-performs even the fescue.
Herbicide treatment dates varied depending on the weed species in the pasture, but typically fell in the month of June with some stretching into July.
As graziers in the Midwest know, tall-fescue pasture goes through a spring flush that overwhelms broadleaf weed emergence. As the fescue slows down, the broadleaves get a chance to germinate, thus the early summer treatment dates.
Bradley said that regardless of a broadleaf weed like ragweed’s nutritional value, if cows avoid it, ragweed and other weeds have the propensity to overrun grass.
“I put ragweed in the top five of the most common weeds in Missouri pastures. If grazed young it is acceptable, but often, late in the season, pastures turn into ragweed pastures. Cocklebur fits into the category as well. These are weeds that we can control relatively easily.
“What you don’t see from our initial reports is the measurements we’ve taken in the spring following the treatments. These show reduced weed pressure in the pastures that were treated with herbicide. In the pasture that didn’t get treated, weed pressure is the same or greater than the year before,” he said.
Weed management in pasture is affected by economics, and is often an early cut in expenses. “If somebody asked me what the percent of treated pastures in Missouri was, I’d say it’s pretty low, probably less than 10 percent,” said Bradley. And for all the research and producers meetings that show the benefits of management-intensive grazing, pasture acreage under that practice remains low.
The research by Bradley and his team shows that there are gains to be made in the middle of the management continuum.
“The million dollar question,” said Bradley, “is if you are going to treat pastures as we did in the study, how often do you need to do it?”
“The seed bank in a pasture is rich, and you will see emergence of weeds that you might not have seen recently due to events like drought conditions and over grazing.
Regardless of what causes that pasture canopy to open, we get weeds as a result. The best thing I can say is that the more you maintain your grass as a healthy stand with proper liming and fertility and by not over grazing, the less opportunity you give weed seeds to compete. But it is a never ending battle.”
Bradley added that aside from the herd’s obvious preference for weed-free grazing, over the course of the study’s three years and three locations, forage yield data was variable, but areas that were treated for weeds offer a starting point for better grazing.
“I would say that after looking at our one-year-after treatment data, it looks consistent. The spring after treatment we see the untreated pasture with greater weed content and the treated sections with fewer weeds and a greater grass component,” he said.
For producers ready to get legumes back into the mix, that might be the right time to start anew. “It’s hard to bring legumes back in the same season you control the weeds due to residual control from the herbicides used,” said Bradley. “But we can frost seed the next season and have good results.”
Weed ID questions?
If you have questions about what type of weeds you find in a pasture or row-crop field, University of Missouri Extension has answers waiting online. Check out http://weedid.missouri.edu. Kevin Bradley, has amassed a database of some 400-plus weeds, including pictures and detailed descriptions.