Southwest Yard and Garden
by Marisa Thompson
Figure 1. Adult emerald ash borers are shorter than a penny (Howard Russell, Michigan State University, Bugwood.org).
I’m concerned about the threat of the emerald ash borer in New Mexico. Should residents and cities be planting ash trees?
- Concerned Citizen of Otero County via County Agriculture Agent, Sid Gordon
The first step in dealing with what looks to be an imminent invasion of emerald ash borer (EAB) in New Mexico is educating ourselves on how this pest works, what to look for, and how to report anything suspicious.
Since 2002, when EAB was first identified in Michigan, it has killed or harmed hundreds of millions of ash trees in 31 states, including Colorado, Texas, Louisiana, and Oklahoma. Many experts believe New Mexico could be next on the list, especially considering the major interstates that connect New Mexico to Colorado and Texas. Scarier still, it could already be here and just not have been identified yet.
The EAB is a pretty, narrow-bodied, metallic green, wood-boring beetle (Fig. 1) that may cause minor foliar damage while in its adult stage, but the larvae feed on the inner bark (vascular system) of ash trees and are so aggressive that even healthy ash trees can die within two years. Another scenario is that the EAB larvae kill an ash tree slowly, taking up to four years before symptoms are even visible. That information is from the Colorado State Forest Service, and they should know since the EAB was confirmed in Boulder, CO, in 2013.
Dozens of ash species can be found across Europe, Asia, and North America. One species native to New Mexico and found mainly in the southwest part of the state is the Arizona or velvet ash (Fraxinus velutina). Green ash and white ash are native to other parts of North America and have been planted widely in New Mexico. Raywood ash is a commonly found ash cultivar native to the Mediterranean. And the popular Modesto ash is actually a cultivar of our own Fraxinus velutina.
There is promising USDA breeding research on the development and testing of new ash hybrids that may be resistant to EAB. Until they are fully tested and readily available, what can and should we do about EAB risks in New Mexico?
I checked with city parks experts from Santa Fe, Albuquerque, and Las Cruces about their EAB concerns. I also interviewed NMSU Extension Agents from Bernalillo and Doña Ana Counties, six nursery owners and managers from all over the state, and several NM Department of Agriculture and NM State Forestry experts for recommendations. Here’s what they all agreed on:
1) Now is a good time to decrease new ash plantings and consider removing ash trees that are not performing well because those are likely more attractive to EAB than healthy trees. Provide existing ash trees with adequate irrigation. Examine ash trunks and major limbs for possible evidence of EAB infestation.
2) Ash trees have become too popular in our municipal and residential landscapes in New Mexico (and across the country), increasing the vulnerability to EAB attack. So many ash trees have been planted in our cities that the situation in Boulder County, Colorado could be repeated here. In order to diversify our tree populations, select native or adapted species that do well in your area. We should NOT be planting invasive species like saltcedar (Tamarisk spp.), tree of heaven (Ailanthus altissima), or Siberian elm (Ulmus pumila).
3) Do not move firewood to or from another state—always buy local and burn it where you buy it. This rule is not just true because of EAB threats; other borers and pests can be hitchhikers too. As Tom Zegler, NM State Forestry Special Projects Forester, says, “The emerald ash borer infestation in New Mexico is only one load of firewood away.”
Dr. John Formby, entomologist and Santa Fe-based Forest Health Program Manager with NM State Forestry, warns that the potential problems associated with EAB increase when ash trees are planted together with minimal species diversity, almost as a monocrop, which is unfortunately common in public areas. Formby suggests that if residents know the risks involved with EAB infection and still want to use them in the landscape, select a diverse mixture of trees with only a few, say 10%, ash trees, and be sure to space them out.
NMSU Extension Entomologist and NMDA State Entomologist, Dr. Carol Sutherland, offers encouraging advice that can make an EAB scout out of all of us. “Keep looking,” she says, “and take samples and photos of anything different or unusual occurring on your ash trees. When EAB arrives, it will most likely be YOUR problem in YOUR ash trees, not someone else’s. Dead and dying trees of any size can be dangerous, difficult, AND expensive to remove. Since ash has been a popular urban tree in several New Mexico cities for several decades, their continuing loss could definitely change the appearance and ambience of neighborhoods, parks, and recreational areas. What EAB confirmation takes is for an interested, involved citizen somewhere in New Mexico to pay close attention to his or her ash trees, starting again this spring when trees should produce a full canopy of leaves. Photograph D-shaped emergence holes (Fig 2) in ash tree bark, any increasing die-back in the canopy, and any peeling bark. Photograph loose bark from above and especially on the underside if you see any broad, flattened, winding tunnels. Promptly submit these photos plus your contact information to one of our many professionals who are trained and ready to help with the next steps. Chances are, we’ll contact you for a field visit to collect more specimens for verification.”
These trained professionals can be found at NMSU County Extension Offices (find your county’s Extension Office at http://aces.nmsu.edu/county/), the NMSU Plant Diagnostic Clinic (http://aces.nmsu.edu/ces/plantclinic/), any of the six NM State Forestry District Offices, or other NM State Forestry Programs, including the Forest Health Program Office in Santa Fe. We are all taking the EAB threat seriously. Remember, it is important to get a positive EAB identification before cutting down trees.
Dr. Sutherland adds, “Don’t expect to see actual EAB beetles first and damage second. These beetles and evidence of their initial attacks are easily overlooked.”
Colorado State Forest Service Emeral Ash Borer Information Site
City of Boulder Colorado Emeral Ash Borer Program
City of Boulder Colorado Emeral Ash Borer Program
Photos of ash trees in my neighborhood:
Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at email@example.com, or at the Desert Blooms Facebook page (@NMDesertBlooms)
Please copy your County Extension Agent and indicate your county of residence when you submit your question!
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/
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, office: 505- 865-7340, ext. 113.