Piñon Needle Scale – Part 2: Suppressing Pest Populations

Question:

I took these photos on one of the piñon trees nearest our house. We have thousands of piñon here on our land and our neighbor’s land, some of which have died within 12–14 days of turning brown. We would hate to see an epidemic, but it does seem to be spreading. What is it and what should we do?

- Paula P., Mora, NM (submitted via NMSU Extension Agent for Mora County, Suzanne DeVos-Cole)

Answer:

Last week, NMSU Extension Entomologist/NMDA State Entomologist, Dr. Carol Sutherland, and NM State Forestry Forest Health Program Manager, Dr. John Formby, explained why timing is crucial for controlling an infestation of piñon needle scale (PNS). As with most pest problems, the goal isn’t 100% eradication, partly because that’s impossible and not necessary. The winning strategy is to suppress pest population levels.

Black specks on these older, browned piñon needles at a park in Albuquerque back in in March 2018 are a sign of a piñon needle scale infection. Photo credit M. Thompson

As Dr. Formby pointed out, PNS has been reported in forest piñons around the state, but the damaging infestations tend to be more of an urban issue, “especially because these areas experience chronic, epidemic populations” and because urban piñons tend to be stressed in our landscapes. The main stressors are water, not enough rooting area, soil compaction, water, and water. Piñons are native to higher elevations in New Mexico and are drought-tolerant, but even native trees need supplemental water when planted in yards and parks. For tips on how much to water and where to apply the water (hint: not just at the base of the trunk!), visit https://nmsudesertblooms.blogspot.com/, type “water” in the search prompt, and check out those top three columns.

The assignment from last week was to get close to the piñons near you and to look for “little black beans” (female PNS live under those tiny bumps) on the needles and “dryer lint” (waxy filaments and egg masses laid by the females) on the trunk and branches. That “dryer lint” is what you’re going to focus on at this time of year. If you see the black spots on needles but don’t see the “dryer lint,” check back in a few days. Depending on temperatures, you’re likely to find the “dryer lint” (if your tree is infested) between February and April—earlier in southern New Mexico and later in northern parts of the state.

Here are Dr. Sutherland’s recommended steps for getting PNS under control using non-chemical means once the “dryer lint” is visible:

1. Using a garden hose with a pressure sprayer, give each tree a periodic “power shower” as long PNS is active. Crank up the water pressure as high as you can. Starting at the top of the tree, use a forceful drenching spray on the foliage, twigs, branches, limbs, and trunk. Work your way slowly and thoroughly around the tree as best you can, from top to bottom—don’t forget the trunk or any other areas where that “dryer lint” is.

2. Let the tree drip for, say, 20 minutes before raking and bagging whatever fell off it during the shower. You’re removing adults, eggs, and crawlers—but nowhere near 100% of them in one shower.

3. Wait about a week and repeat on each tree.

4. One small purchase that will be really worth your while for monitoring PNS during the year—and other insects, too—is a white dishpan. Use this as your “beat bucket.” Find something you can use like a bat to whack branches and foliage over your white dishpan. Look in the dishpan for minute crawling insects. Adults will not look much different from very young crawlers. After a moment, the live ones will struggle to their feet and start moving—easy to see against a white background. As long as they’re moving this spring, they can be treated (high-pressure water) OR by another means (see below).

5. As long as you’re finding crawling things, rake under the tree after the “power showers,” bag the debris, and dispose of it.

Piñon tree in an Albuquerque park (March 2018) has browning needles, but it wasn't until I got close that I could see the piñon needle scale evidence. Photo credit M. Thompson

Sutherland adds, “If ‘power showers’ aren’t a possibility for some or all trees of concern, then it’s time to consider insecticides. Their effectiveness varies. No matter what product you consider, Read the labels on all products before you do anything and re-read these product labels before using them again . Some products may be phytotoxic to needles, so do not use them on any new green growth—the brown, dead needles will fall anyway. Among the active ingredients to consider in an insecticide are horticultural oils, insecticidal soaps (NOT dish detergent), possibly dinotefuran, and imidacloprid. You’ll need application equipment for these products as well as all safety gear recommended on the label.

“There is no once-and-done treatment for these insects. This whole monitoring and treatment program will be an annual project for you, so keep the dishpan handy, perhaps tapering off after several years. While you’re getting this treatment program going, don’t forget to make provisions for irrigating your valued trees. They’re already stressed by insects as well as by environmental conditions over the years.

“Good luck with this challenging pest!”

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!