January 25, 2019
As surely as spring will come no matter what winter has wrought, it is nearing the time to start scouting pastures for emerging sericea lespedeza. And now is the time to get the best practices in place to control that perennial pest when it shows up, says Scott Flynn, a field scientist with Corteva Agriscience, Agriculture Division of DowDuPont.
“It’s not necessarily that there is a perfect answer with herbicides or with grazing or with burning, Flynn says. “It’s more that we know that integrated pest management works. You have to have options available if an event such as weather robs you of your preferred method of control.”
When the plant is very small in the early spring, intensive, rotational grazing may work to weaken its position in the pasture. But as it grows more stemmy and woody, it becomes less desirable and cattle find it so distasteful that they will literally eat anything else first, Flynn says.
“What forage agronomists have learned, is that you can get some control with rotating large numbers of cattle onto small pasture paddocks. In that scenario when you get it grazed down, the regrowth comes back palatable and it doesn’t hit that woody stage that they won’t touch,” Flynn says.
In pastures where that isn’t practical — or where it’s already too late for that approach, it may work to apply a herbicide such as PastureGard HL which can be applied from the time it is about 8 inches tall to early September and provide good control, he says.
“One thing that’s good about PastureGard HL is it doesn’t have any grazing restrictions and it won’t damage the native grasses,” he says. “Early in the season, you can apply about 12 ounces to the acre in most of Kansas, Missouri and Nebraska. Later, when it is bigger, it is good to increase the rate to about 16 ounces.”
For ranchers in areas where it is practical, late summer burning has been shown to be an effective control to prevent sericea plants from setting seed.
“In areas where you have enough fuel out there to complete a late-season burn, that really works well. But there are areas in any given year where it has been drier, or pastures have been grazed more heavily, and there just isn’t enough fuel load to complete an effective burn. That’s when a product like Chaparral can be used in late summer or early fall to kill it and prevent it from spreading seed,” Flynn says.
Finally, he says, the best protection against any weed pressure, including sericea lespedeza, is a good, dense stand of competitive forage.
“If you have desirable forages that are healthy and lush, it can help suppress weeds,” he says. “You can use a herbicide such as PastureGard HL to control the emerged sericea and give your desirables a competitive advantage.”
He warned, however, that because sericea is a very hard-seeded plant and seeds can live in dormancy in the soil for a couple of decades and then germinate and grow when conditions are favorable.
“I’ve seen cases where there are pastures that haven’t been hayed or grazed in three years and where there is no sign of sericea. But as soon as you graze it down or mow it, you’ll see the sericea popping back up. It’s a tough weed.”
That, he says, is why ranchers need to be prepared to use more than one method of control.
“There’s always the temptation to just do what worked last year,” he says. “The problem is conditions may be different this year, and you have to be prepared to do whatever you need to do to manage it this year.”
That may mean that you take advantage of an opportunity to use whatever works at the time to knock it back, he says.
“You may hit it with herbicide in mid-June, intensively graze pastures into the summer then let them rest and regrow enough fuel to burn in the fall. It’s more of a matter of managing the problem. At the point we are now, eradicating it may not be possible. We just have to learn to control it so it can’t take over,” Flynn advises.
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