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Rangeland weed control: Options may be limited but are effective

Farmers and ranchers who have sneaking suspicions that telephone sales pitches for pasture and rangeland herbicides might sound just a bit too good to be true should trust their gut instincts.

“I know of no reputable companies using tele-marketing to sell herbicides,” said Allan McGinty during the recent Ag Technology Conference at Texas A&M-Commerce. “Most phone solicitations offer watered down versions of herbicides,” said McGinty, a Texas A&M range specialist from San Angelo and a co-developer of the Texas “Brush Busters” program.

He also cautioned producers to shy away from recommendations that lack a legitimate seal of approval.

“The Extension Service and the Natural Resources Conservation Service provide sound, dependable recommendations. But be wary of your neighbors. Some of the concoctions they might recommend could be illegal or toxic to animals.”

He also urged producers to distrust recommendations by retail outlets with little experience in rangeland weed control.

Even with those caveats, ranchers have, if not abundant options, at least some materials that work.

“The key is to know the herbicides,” McGinty said. “There are not that many available for rangeland and pasture.”

He said 2,4-D, a standby for years, remains an integral part of rangeland weed control. “It has survived a lot of changes in regulations.”

He explained that 2,4-D comes in numerous formulations, broken down into two basic groups, amines and esters. “Oil-based esters cost more but are a little stronger,” he said.

Water soluble amines cost less and control a more narrow spectrum of target plants. “In West Texas, esters might work better. In East Texas, producers use amines more often because drift is less likely.”

Soil activity with either is unlikely, but McGinty cautions about volatization, especially on hot or windy days. “Volatization could burn leaves or kill non-target plants, even miles away” he said.

Primary targets for 2,4-D are annual weeds. “We see little activity on most perennial weeds.”

McGinty said Banvel (dicamba) works better for perennials.

“We've used it in rangeland and pastures for years. It provides good control. Banvel has significant soil activity, so users should be careful when making applications near the rootzone of non-target plants.”

Drift potential is minimal and Banvel offers a broad spectrum of control. It's also more expensive, approximately $80 per gallon compared to $20 a gallon for 2,4-D.

Tordon 22K (Picloram) fits a niche that no other herbicide fills, McGinty said. “It kills succulents such as prickly pear, cholla, tasajillo and dog cactus. It has soil activity so be careful and do not apply near the rootzones of non-target plants.

“This herbicide needs rainfall to move into the soil and breaks down quickly if exposed to sunlight. Whatever a producer mixes up he should use as quickly as possible. Tordon 22K may not be a good choice during long dry periods.”

Ally, the only non-restricted use herbicide McGinty mentioned, poses little drift problems, but is not effective on prickly pear. Its primary use on rangeland is for broadcast applications to control annual and perennial weeds.

McGinty said herbicide combinations offer advantages and have been around a long time. Weedmaster is a combination of 2,4-D and dicamba. “Grazon P+D is a combination of 2,4-D and picloram. Both sell for approximately $26 per gallon making either an excellent choice for use as a general weed control herbicide for rangeland McGinty said.

Woody plant control requires different herbicides, McGinty said.

“Remedy is the Roundup of the range market. If I was restricted to only one herbicide for rangeland woody plant control, this would be the one I'd pick. It offers flexibility and is almost foolproof.”

McGinty said Remedy can be mixed with oil, either diesel or vegetable. “Apply it to basal stems or spray on cut surfaces along fencerows.” Used in this manner, Remedy will control most woody plant species.

Controlling woody plants, he said, requires a bit more effort than annual weeds. “Most woody plants are sprouters,” he explained. “When they're top is removed, they sprout back from an underground budzone.

“We have to get the herbicide to these buds. That's the secret to control.”

He said Remedy and diesel is a good choice year-round. “But summer, with temperatures above 90 degrees, is ideal. The usual recipe is 15 percent to 25 percent Remedy and the rest diesel.”

The process: Cut stumps and spray the outside edge, the cambium layer. That's where the herbicide translocates to the buds.

“If a spray just misses a corner of the stump, it will sprout. We have to cover it all the way around.”

He also recommends a flat cut. A cut that slopes allows the herbicide to flow away from the high edge.

McGinty said Remedy has “almost no soil activity. But it can volatize on a hot day.”

He said Reclaim mixed with Remedy can be sprayed on mesquite leaves and from there translocates to the roots.

“Timing of the application is critical,” he said. “Don't apply when the plant is dormant. When mesquite puts on new leaves, the sap (carbohydrates) begins to move up. If a rancher sprays too early, he'll kill the top but the plant will resprout the next year.

“Wait until mesquite leaves reach a dark green color, about 45 days after bud break. At this time, carbohydrates start translocating down to the root system, so an application will produce a good root kill.”

He said an application too late, would hit the foliage when there is less downward flow and control would not be as good. Hand-applied leaf sprays of Remedy plus Reclaim can be made from 45 days after bud break through July in East Texas and South Texas.

The spray period can exend into September through the rest of the state.

McGinty said Reclaim is the key to killing mesquite through the leaves. “Remedy alone will not take out mesquite through the leaves.”

He said other herbicides have specific niches. “Velpar L is very effective for cedar control, but is also deadly on oaks and other desirable woody plants. As such it should be used with caution.”

He said Spike 20P is a pelleted, soil applied herbicide used a lot in West Texas for control of catclaw, creosotebush, tarbush and whitebrush.

“Watch its soil activity, though. This herbicide will also kill desirable woody plants such as pecan or oaks if it is picked up by the plants' roots.”

McGinty said adjuvants are important ingredients in rangeland weed control recipes. “Options include diesel, oils, emulsifiers, penetrants and surfactants.

“Most herbicides are applied to plant leaves. Leaves have a waxy coating and water-based products tend to bead up and roll off. One of the most common and important adjuvant is a Surfactant which destroys the surface tension of water based sprays, improves wetting and thus uptake.

“I always recommend surfactants in water-based herbicides. Something as simple as liquid dishwashing detergent will work in a pinch.”

McGinty's final caution was that users, regardless of the herbicide, the locale or the target plant, should “read the label and stay within the prescribed uses.”

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