Almost no one argues against clover in pastures. The legume just has too many benefits, improving both soil fertility and animal performance.
Unless, that is, you can’t see the forage for the weeds.
Then if zeal to save the clover keeps you from spraying a significant weed problem, Kevin Bradley respectfully will suggest that the grazing lost to weed pressure might outweigh the benefits of the clover.
Spraying usually takes out the clover, at least for a season, concedes the University of Missouri weed scientist. But clover can also be replaced after a weed problem is under control.
Bradley knows cows prefer to graze clean grass versus a weedy mixed pasture. He’s studied grazing preferences when cows could choose.
In a series of trials, Bradley fitted cows with GPS collars that recorded when and where cows actively grazed. After establishing a baseline of their grazing patterns in a particular pasture, he sprayed half the pasture and documented changes in their grazing.
Weeds and grazing preference
Before he sprayed his Albany, MO, site, cattle grazed the weedy 90 acres of fescue and clover evenly. Then for a month after he sprayed half the pasture, their grazing remained evenly distributed.
But as treated weeds died and untreated weeds grew larger, preferences changed.
For the next three months, cows grazed the treated half of the pasture 73 to 84 percent of the time. Averaged across the grazing season, cows grazed the treated pasture 74 percent of the time, versus 26 percent on the untreated side.
The cows clearly preferred clean fescue to a mix of weeds, fescue and clover.
Forage yields also were higher in the treated side.
“In a lot of our sites, on our untreated side where we didn’t spray a herbicide, the weed component of that total yield was 50 percent or more,” Bradley says.
So how bad do weeds have to be to justify spraying for weed control that will also sacrifice the clover?
That’s tough to pinpoint because of all the variables, Bradley says. But it’s probably before weeds reach 50 percent of pasture production by weight, he says. “Although there’s very little research that’s been done in this area, it’s very likely that the threshold is well below that level.”
Weeds out, clover back
Of course, few producers will take and weigh clippings as Bradley did. If you estimate pasture composition by eyeballing the canopy, it won’t take 50 percent weed canopy to equal 50 percent of pasture production by weight.
“If you see 50 percent of a given area in weeds, then probably more than 50 percent of the harvested forage will be weeds,” he says.
When weed density is significant, spraying presents a real opportunity to improve productivity, Bradley says.
When weeds are bad, he recommends solving the weed problem and then bringing back the clover. Many soils will have a native supply of seed that will produce a year after you stop spraying. Or you can spend a few dollars and seed new clover into the system.
From there, the key is keeping a canopy to shade the weed seed in the soil and keep it from germinating.
“As long as we’re maintaining good health and vigor of the fescue through good fertility and good grazing management, you can likely go years without having weeds germinate again,” he says.
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