Writer: Norman Martin
TUCUMCARI - In the space of a century, drought-tolerant field bindweed has overrun New Mexico, spreading with abandon from suburbs to sun-drenched fields.
To fight back, New Mexico State University scientists are combining a microscopic bug from Greece and chemical herbicides.
"Once this weed gets a foothold, it flourishes," said Mark Renz, a weed specialist with NMSU's Cooperative Extension Service. "And if the conditions aren't good, it can wait more than 50 years to germinate." At its worst, field bindweed forms dense mats that block sunlight and nutrients, reducing crop yields and causing significant harvest problems.
A cousin of the morning glory, field bindweed came to the United States from Europe in the late 1700s. The pest likely arrived in New Mexico in the 1890s along with other adventurous pioneers. Two decades later, it had infested eight counties. Today, it's in all 33 New Mexico counties, Renz said.
One factor that makes field bindweed such a pest in New Mexico is its drought resistance, thanks to a massive root system, said Leonard Lauriault, a forage agronomist at NMSU's Agricultural Science Center at Tucumcari. While two-thirds of the plant's roots remain in the top two feet of soil, the weed's taproots can power down more than 30 feet, the height of a three-story building.
Stopping such a toughie isn't easy. Chemical control alone is difficult and expensive. But two decades ago scientists discovered that a microscopic mite from Greece was effective for biological control. After being quarantined and tested, the tiny bugs were first released in Texas in 1989. Tests began at NMSU's Tucumcari science center 12 years later.
The parasitic mites feed on field bindweed, damaging the leaves. Virtually invisible to the naked eye, they're introduced to new areas either naturally or by placing mite-infested bindweed plants in the field. But they're not a perfect solution because they're parasites.
"And a parasite is not going to kill off its host," Lauriault said.
This is where NMSU's new integrated pest management program comes into play. Biological controls like the mite are being combined with herbicide treatments. Cultural practices such as mowing and grazing are being used to defoliate the bindweed and force the mites to concentrate on the weed's roots.
"We need the mites to move," Lauriault said. "As long as they're happy on the plant, they're not going anywhere. Now, we're trying to combine herbicide treatments with mites to get a synergistic effect."
The mites normally feed off the plant's roots during the winter and move back to the leaves in the spring. This season, NMSU researchers are testing a variety of herbicides to kill the top of the weed and push the mites toward the roots. The scientists' goal is to kill the top of the plant and still allow the slow moving mites to mosey along. Normally, the mites don't move much more than one foot a year.
To learn how far the mites move down into the root system, Lauriault and his research team in Tucumcari are evaluating the effectiveness of several herbicide treatments this summer using 8-inch diameter soil probes. The probes will also allow NMSU entomologist Dave Thompson, based in Las Cruces, to measure the number of mites that have migrated to the weed's roots.
Using NMSU's specially equipped quarantine laboratory in Las Cruces, Thompson meticulously counts the mites, which can number in the hundreds, from samples of the plant's leaves, crown and roots. "Let's just say it involves a lot of microscope time," he said.
The information could be even more valuable when New Mexico's five-year drought subsides. "With this drought, a lot of producers have simply stopped farming their land and the field bindweed has taken over," Renz said. "If we ever do get water, then we're going to have even more problems."
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