Wet weather a boon for piñons

Much like humans, healthy trees are better able to ward off “bugs” that threaten their well-being. That’s why after years of drought, this year’s wet winter bodes well for piñon trees across northern New Mexico, at least in the short-term.

“Drought stress is the primary factor that sets healthy piñons up for attack by beetles,” says Santa Fe arborist Tracy Neal. “Loss of foliage and the corresponding loss of energy— the result of continued attacks by piñon needle scale — is another thing that makes piñons more susceptible to bark beetle predation. I don’t expect the cold this winter to have any real effect on bark beetle populations. The rains last fall and the snow this winter will do a lot more to help the trees resist bark beetle attacks in the coming season, at least in the spring.”

Scott Ferrenberg concurs. The assistant professor of biology and director of the Global Change Ecology Lab at New Mexico State University said, “Drought stress combines with warmer temperatures to leave trees less defended and easier to kill.” NMSU is home to the state’s Extension Master Gardener program, which has chapters in 15 counties, including Santa Fe County.

There are hundreds of species of bark beetles in the United States. The majority are native and cannot or do not kill trees, instead utilizing already dead wood or small portions of living trees, according to Ferrenberg. The Ips confusus bark beetle is the one that most commonly preys on New Mexico’s piñons and is among many dozens of species that kill trees worldwide.

Bark beetles bore straight into the bark, leaving a small round hole on the surface. In some cases, the tree will defend itself with what is called a “pitch tube,” a drying blob of resin that shows the tree’s efforts to expel and mire the beetle. Even as many as 10 of these attacks typically are not enough to really harma pine tree, Ferrenberg asserts. But these early attackers will cause the production and release of certain tree chemicals that will signal distress and attract more beetles.

If you see evidence of bark beetle activity and can intervene, you might save the tree, says Ferrenberg. “Killing the beetles when or where they are visible, wrapping the trunk and stem of the tree in anything that keeps the beetles off the bark (such as nylon window screen), and getting water to the tree’s roots are the best options if the attack is in progress.”

“Getting water to trees that are drought-stressed is the key to avoiding or reducing attacks in the first place,” he explains, noting the need to balance watering practices with current precipitation patterns and drought conditions.

Neal agrees. “Inwarm, dry winters such as the one we had last year, it’s helpful to water trees once a month,” he says. “This winter that won’t be needed in most areas. Once the heat arrives and the soil dries out, usually in late May or June, it’s a good idea towater every two to threeweeks to keep the trees sufficiently saturated. This approach is recommended at least through September, barring any significant rains.” If bark beetles start to build up again, Neal recommends watering every two weeks during a hot, dry period. He adds, “Newly transplanted trees that do not have a well-developed root system will need to bewatered every three to four days to keep them hydrated. The stress from root loss at transplanting makes them especially susceptible to bark beetle attacks.”

For a water-wise guide to planting and watering trees in New Mexico, check out this pdf from the State Engineer’s Office: www.ose.state.nm.us/WUC/PDF/TreeBrochure.pdf.

The U.S. Forest Service has compiled some of the most frequently asked questions about bark beetle activity in the Southwest, available here: www.fs.usda. gov/detail/r3/forest-grasslandhealth/insects-diseases/?cid=stelprdb5228384.

Kathy Haq is a Master Gardener; she returned to Santa Fe about a year ago after living in Southern California for nearly 20 years.

photo courtesy James St. John