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New Mexico State University

New Mexico State University

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Drought Increases Bark Beetle Infestation throughout New Mexico

ALBUQUERQUE - Two years of severe drought have intensified bark beetle outbreaks throughout New Mexico, causing fatal infestations of thousands of acres of evergreen trees, a forest entomologist with New Mexico State University said.

Aerial surveys this summer showed that engraver beetles killed more than 13,000 acres of ponderosa and piņon pines in patches throughout the state, and more damage has been detected since September, said Bob Cain with NMSU's Cooperative Extension Service. Other species of bark beetle that attack high-elevation conifers have infested another 33,000 acres, killing ponderosa pines, spruce, and Douglas and white fir trees.

"We're seeing a tremendous increase in the number of areas affected plus a severe intensification of attacks in the infested zones," Cain said. "Certain parts of the state have experienced two years of acute drought during the winter and summer, and it's led to an immense buildup of bark beetles in wooded areas."

The largest outbreak is near Quemado in Catron County, where a new housing development is planned on about 3,000 acres of wooded area. Engraver beetles in that zone have killed more than 1,000 acres of piņon pines, Cain said.

"It's a pretty significant outbreak," Cain said. "In that area, we're seeing all sizes of piņon being killed by beetles, from sapling size to trees over 20 inches in diameter. It's devastating the wooded areas because wherever the beetles attack it's basically 100 percent mortality? they're not leaving anything behind."

Other infested regions include an area in the Guadalupe Mountains near Queen in Eddy County, and zones in Ruidoso, Santa Fe, Pecos and Las Vegas. Beetle infestations are also increasing around housing construction sites in the east mountain areas of Albuquerque, Cain said.

Bark beetles feed on the phloem tissue, the substance just beneath the bark that moves the sugar from the foliage to the roots. The beetles, which are slightly larger than a pinhead, also introduce a fungus that blocks water movement from the roots to the top of the tree.

Healthy, vigorously growing trees are best equipped to withstand beetle attacks because of their active resin systems that deter beetle colonization. When the beetle bores into a healthy tree, resin exudes through the wound and may prevent the beetles' entry.

Consequently, the beetles prey on water-stressed trees, taking advantage of drought conditions that severely weaken natural defenses. Many trees are weakened by rocky soils, excessively sandy soils or mechanical injuries to roots or trunks caused by construction. Drought exacerbates the problem, attracting more beetles and causing more intense infestations.

Once bark beetles have successfully colonized a tree, it cannot be saved, Cain said.

"Infested trees should be removed, burned or run through a wood chipper as soon as possible to protect surrounding trees from attack by emerging beetles," he said.

Homeowners should also check green firewood because bark beetles emerging from infested firewood account for many tree losses near homes and in urban settings. If firewood has been stored for at least one season, the beetles won't be present, but homeowners should take precautions with green firewood collected or purchased in summer when temperatures are high, Cain said. Infested firewood should be stacked in direct sunlight and covered with clear plastic in piles no larger than 4 feet by 4 feet by 4 feet, which creates a greenhouse that can kill the beetles.

Tree thinning in overcrowded wooded areas is also a good precaution against bark beetles, because it reduces the need for trees to compete for scarce water.

"A lot of beetle outbreaks occur because the forests are dense," Cain said. "Thinning the forests will make the trees less susceptible to beetle outbreaks during future droughts."