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New Mexico State University

New Mexico State University

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Snakeweed's Genetic Makeup Could be Key to Better Control Methods

LAS CRUCES - Broom snakeweed populations found in northern New Mexico have more compact architectures than the larger, more open brooms found in southern New Mexico snakeweed populations. These morphology differences translate into genetic differences that may help ranchers better control this weedy shrub that infests about 60 percent of New Mexico's rangeland.

Broom snakeweed is a major range weed in New Mexico, as well as throughout the western United States. "It can exist under many environmental conditions. It's a problem because it's poisonous to livestock and competes with more desirable forage," said Tracy Sterling, a weed scientist with New Mexico State University's Agricultural Experiment Station. "We were interested in finding out snakeweed's level of genetic variability, which might affect how sensitive certain snakeweed populations are to biological controls."

Biological control is the control of undesirable plants and animals by devising ways to break their reproductive cycles or by introducing predators and diseases. It is an alternative or supplement to chemical and cultural control.

"Snakeweed is difficult and expensive to control using mechanical and chemical approaches in large, rangeland areas," Sterling said. "That's why biological control with insects or plant pathogens may be a more practical and economic approach to reducing broom snakeweed populations in the long term."

In her study, Sterling looked at the genetic makeup of 60 broom snakeweed plants collected at random from the following rangeland areas in New Mexico: Bayard, Clovis, Corona, Des Moines, Las Cruces, Lovington, San Simon Sink and Tatum.

"We found a lot of variation between different populations across the state," Sterling said. "But when we looked within a population, those individual plants were very similar to one another."

She said this makes sense because snakeweed is usually cross pollinated by insects. "If there's a large geographical distance between two populations, it's hard for the pollen to be shared, so you see more variability between populations than within populations," Sterling explained.

Next, she plans to study whether certain biological controls work better for particular snakeweed populations. A weevil and the red-kneed grasshopper are the most promising biological controls for snakeweed, she said. The grasshopper defoliates entire snakeweed plants. The weevil lays its eggs in the roots or stems of snakeweed plants; when the larvae hatch, they eat the roots and kill the plants.