Recent Rains Bring Problems with Rangeland Weeds and Brush
Date: Aug. 20, 1997
Editor: D'Lyn Ford (505) 646-6528, dlford@nmsu.edu
LAS CRUCES -- Recent moisture has caused almost everything growing on the state's rangelands to green up, including some undesirable plants, said a brush and weed specialist with New Mexico State University.
"With more precipitation, we have more plants growing, so we have more weeds," said Keith Duncan of NMSU's Cooperative Extension Service. "With a wet year, we also tend to notice the brushy plants more, because they're growing faster."
Unusual growth in weeds and brush can cause problems for farmers and ranchers. This year, weeds are coming up that are totally unfamiliar to ranchers or have not been seen in many years. "We've had weeds showing up that even the best of us had to go back to the books and look up," Duncan said.
Cocklebur, filaree, pingue and several yellow-flowered plants from the sunflower family are some of the weeds that have shown up this year. The first step in weed control is to correctly identify the weed problem. Herbicide rates and application processes vary according to plant species and growth stage. "If you can't identify a weed, the best thing to do is pull some samples and get it identified, so you'll know if it is a problem or not," Duncan said.
When spraying weeds, ranchers should be sure the sprayer is properly calibrated. This prevents both waste and expense of over- and under-application, he said.
Different weeds are more susceptible to herbicides at different times, Duncan explained. Annual and biennial weeds should be sprayed when they are growing rapidly and before flowering. The susceptibility of perennials and woody plants depends on the species and herbicide used.
Brush also has gotten a boost from the moist weather. "Because of the wet year, the brushy plants produce more fruit," Duncan said. "Russian-olive is making a bigger fruit that's showing up more. We're noticing the mesquite pods more, because they're really making a lot more beans."
On the positive side, brush provides browse and cover for wildlife and livestock in pastures. If too dense, however, brush can reduce grazing, degrade wildlife habitat and decrease the lifespan of fences.
"If brush gets in the wrong spot, then it becomes a weed problem," Duncan said.
Unlike weeds, the woody plants are perennials, with deep root systems. For the most effective control, herbicide treatments should be matched to specific brush problems.
Along fences and in scattered stands of brush, Duncan recommends a high-volume foliar spray. This involves spraying the plants with herbicide until dripping wet, usually in late spring or early summer.
Basal bark treatments can be used on smooth-barked plants with less than a six-inch diameter. The lower 15 to 20 inches of the stem should be wet with the herbicide solution, but not to the point of runoff. This technique is very accurate and can be used any time of the year except early spring.
On smaller, smooth-barked plants, herbicide solutions should be applied with a straight stream nozzle in a six-inch band around the stem, Duncan said. This band should be 12 to 24 inches above the ground.
When brush is very dense and covers a large area, an aerial broadcast spray works best. While plant mortality rates may be lower than with individual plant treatments, a larger area can be covered with less labor. Optimum timing depends on the plant species.
For more information or specific management recommendations, contact your county Extension agent.