Pasture weed problems result from management errors, says a Texas A&M Extension range specialist.
“Plants respond to management practices,” says Barron Rector. “If a weed problem exists, man created it.”
Rector, speaking at the 2004 Ag Technology Conference on the Texas A&M-Commerce campus, said the way a rancher manages his forage grasses determines what weed problems will occur.
“If he does not leave enough grass, he opens up the land for weed invasion,” Rector says. “On open land, when rainfall hits the soil, it helps weed seed to germinate. And what a rancher does in the fall determines what happens in his pasture next spring. He must leave enough grass to make it through winter. It's imperative that ranchers understand the impact that grazing has on weed populations.”
Rector says when prairies were undisturbed, when only bison and elk grazed, weeds presented no problem. “Those animals grazed differently than do longhorn cattle,” he says. “Before Europeans settled, there was no weed problem. Now, we have no pasture without resident weeds and brush. Human impact is the reason, so we need to learn how to manage the soil better. In much of Texas we manage for drought and stay ready for flood.”
Rector concedes that little rangeland will revert back to its native state, so ranchers need to develop management strategies that allow introduced grasses and native species to compete as much as possible against invasive weeds.
Along with managed grazing, chemical control may be necessary for some species, Rector says. Weed identification also plays a crucial role in management.
He says the top 10 weed problems in Texas rangeland include: purple scabiosa (pincushion), broadleaf sump weed (marsh elder), Carolina nightshade (horse nettle), dewberries and blackberries, green briar, Eastern persimmon, honey locust, goat weed or croton, bitter sneezeweed and Texas squaw weed.
Other problem weeds include rattail, smutgrass, grass burs, bull nettle and milkweeds.
“Look at a balance,” Rector says. “Milkweed, for instance, is harmful to animals but is important to Monarch butterflies.”
He says purple scabiosa is highly invasive “but only with mismanagement of the land. Native grasses compete well against it. Mechanical controls may be effective but are costly. Mowing and shredding may cost $15 to $20 per acre. Other options may be more efficient and cost-effective.”
A new chemical, fluoxypyr, holds promise for several hard-to-control weed species.
“It's a systemic material with soil residual activity,” Rector says. “Water solubility is low.”
Target species include siricea lespedeza, blackberry, prickly pear, locust and others. He says the material is included in PastureGard. Rates should be higher for brush control than for herbaceous weeds.
“We've gone 25 years without a good control (of some of these tough species we can spray on leaves.”
He says a 2 percent PastureGard application early in the summer, when targets are 3 to 4 feet tall, offers good control.
Surmount, a Dow product, also shows promise on woody species as well as broadleaf and annual weeds. Rector says a 3 to 6 pints per acre rate may be necessary for brush control. For weeds, 1.5 to 4 pints per acre may be adequate. Targets include prickly pear, honey locust, Eastern red cedar, Arkansas juniper, persimmon and Osage orange.
Spike 80 DF, applied with a boom, controls green briar.
Rector says other new options are coming along but a total management program continues to be the best rangeland weed control strategy.
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