TLC for trees

Caring for our trees

TREES ravaged by the piñon bark beetle that swept across Northern New Mexico a decade-and-a-half ago still dot the Sangre de Cristo foothills. Their stark skeletons stand as reminders of what could happen during another infestation. The piñon bark beetles, also known as Ips or engraver beetles, are wood-boring insects. Although always present in the area, they become more populous — and more deadly to area trees — in cycles. Ryan Brenteson, a Santa Fe arborist who owns Very Good Tree Service with his wife, Rebecca Sobel, says Santa Fe is probably due for a bark beetle boom. He’s already seeing a big outbreak on the southside of town, off Old Santa Fe Trail. The beetles kill trees as soon as they invade them. The best protection against them, Brenteson says, is healthy trees. “The biggest problem plaguing our trees is drought and climate change,” he says. “We’ve had more, extended periods of dryness. We’re coming off a multiyear drought.” As the dry conditions stretched on through 2020 and early 2021, the U.S. Drought Monitor (USDM) classified Santa Fe as being in extreme or exceptional drought.

These multiyear droughts, dry spells and hotter temperatures put healthy trees at risk. “Most pests don’t attack perfectly healthy trees,” Brenteson says. “Most trees provide their own protection against pests, but they can only do that when healthy. 2020 was a tough year to be an arborist. There’s only so much I can do for trees without nature helping me.”

Keeping trees healthy means keeping them watered. The Santa Fe Municipal Tree Advisory Board, which advocates for the health and proper care of the urban forest, publishes a document with recommendations for watering. “Even old established trees that grew acceptably with no irrigation in the past may need to be irrigated in the future,” it says.

The document, which is available on the advisory board’s website (see sidebar on facing page), also makes recommendations on the depth, area and duration for proper watering techniques. The board advises saturating the top 18 inches of soil at each watering, reaching down to where the root systems of well-established trees live. This method better delivers water to where the roots can absorb it. Watering too close to the surface also creates a habitat for fungus, which thrives in the moisture-rich environment. Eventually this fungus can infect the tree.

Since there are few water-absorbing roots near the trunk, the board also recommends watering far beyond the base of the tree. “Water should be applied starting two to three feet from the trunk and extending out as far as is practical,” it writes. Watering too near the trunk can cause the tree to become rootbound as it draws its roots closer to the base. Decreasing the size of its base means the tree can more easily tip during windstorms.

Soaking the ground sufficiently can take a couple days and may require using devices that will lessen run-off, particularly on hillsides and at homes with clay-like soil, which requires even more water to penetrate. Devices that apply water more slowly include drip emitters, soaker hoses, bubblers and root soakers. In summer, Brenteson advocates watering every other week, particularly if it’s during a period between rainfalls. Residents need to water more often in sandy soil, since the water will just run through the porous ground. He recommends watering once a month during winter. Newer trees require more frequent watering than established trees.

In addition to watering consistently, Brenteson advises applying organic mulch. “We don’t have tons of organic matter in the soil in New Mexico,” he says. “To counter that, put wood chips around the base of the tree. Don’t push the wood chips up against the trunk. Any arborist in town has woodchips. Some will drop them off for free; others charge.”

Other types of organic mulch include shredded leaves, coarse compost and tree trimmings. The municipal tree advisory board recommends building up the mulch to two- to four-inches deep under the tree and beyond the canopy.

If shoring up the health of a tree doesn’t seem like enough insurance against the threat of pests, certified arborists can use trunk injections to further protect prized piñons. However, those injections tend to add up, so most residents pick out a few trees to protect with this method.

Piñons can also be subject to scale, which is a sap-sucking insect similar to an aphid. It drains the trees and stresses them, but the scale doesn’t kill them. Brenteson recommends inspecting trees for the telltale tufts at the end of the branches, which look like cotton under the needles, then spraying off these egg masses. A dormant oil spray can also be applied, though that has to be done at a precise time in the spring. The same goes for a soil injection to protect against this type of pest. Pesticides are a last resort, Brenteson says.

New Mexicans have a special affinity for piñon trees, but Brenteson says a threat to another type of tree is also on the horizon. Native to Asia, the striking green emerald ash borer has decimated trees along the East Coast. First discovered in Detroit in 2002, it is thought to have entered the U.S. on wooden packing materials. It’s only the size of a dime, but it feeds on and kills ash trees many times its size.

Like the piñon bark beetle, once a tree is infested with ash borers, there’s nothing that can be done to save it. Unlike the bark beetle, the emerald ash borer attacks fully healthy trees. The pest has moved into surrounding states, like Colorado, so Brenteson says it’s just a matter of time until the insect finds its way into New Mexico. He recommends watering and mulching to keep all trees healthy and — for trees with particular emotional importance to their owners — he recommends preventative treatments such as trunk injections.

Regardless of the type of tree or the threat, Brenteson says residents should regularly inspect their trees for changes. Dieback throughout the tree or rapid growth at the base can both be signs of major stress. People should also look for holes in the bark to see if insects are boring. He doesn’t recommend using herbicides anywhere, since these products kill both pests and valuable insects and fungus, and suggests avoiding weed cloth, which can prevent moisture from getting into the ground. At the end of the day, it all comes back to water.