Taking Action for Ash Trees: Organic Inoculation

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What can we do about emerald ash borer? From what we know at this point, inoculation tops the list of tangible actions.

Community members have responded to the news of emerald ash borer (EAB) in Addison County with grief and concern. They’ve also responded with a recurring question: What can we do? From what we know at this point, inoculation of key ash trees is an important tangible action.

Here is what we currently know:

  • Emerald Ash Borer kills more than 99% of ash trees in its path. Green, black, and white ash are all susceptible.
  • Unlike its behavior in its native range of eastern Asia, where EAB appears to infest only weakened ash trees (the Manchurian ash), EAB attacks healthy ash trees in North America and is able to infest and kill ash trees of all sizes, from saplings (>1 inch DBH) to mature trees. 
  • Infestation typically begins in the crown, so that’s where you’ll first see foliage die-back.
  • EAB can kill a healthy ash tree in 2-4 years.
  • Ash seeds persist in the soil for just 2-3 years. Research shows that in midwestern sites that were infested with EAB more than a decade ago, ash seedlings were at first abundant (more than 2000 seedlings per acre), but declined to zero after several years on sites with no mature trees to disperse seeds. 
  • Healthy ash trees disperse plenty of seeds during mast years and the seeds germinate well, so if a small number of mature ash trees survive, they can produce abundant seeds for regeneration.
  • Green and white ash are dioecious, meaning that individual trees are either male or female, so seed production requires individuals of both sexes growing within a few hundred yards of one another. Black ash may be monoecious—with both male and female flowers on the same tree—or dioecious.
  • Even healthy ash trees don’t produce seeds every year—some years are “mast years,” with heavy seed production.
  • Inoculating ash trees has proven very effective against EAB mortality.

Our conclusion? Inoculating a small number of ash trees is a concrete action we can take—a small gesture toward protecting a few seed trees. For some, inoculating a beautiful yard ash may be a matter of aesthetics or economics (since it’s cheaper, at least in the short run, to inoculate a tree than to pay to have it removed). But beyond that, in our family forests, inoculating a handful of trees is a gesture toward helping the species persist, an intention to give back to the trees that give so much to us. 

Richard, from Trees Vermont, inoculates ash trees in Bristol with the organic pesticide, Azasol.

From our perspective at Vermont Family Forests, inoculating only makes sense if the pesticide being used does not do more harm than good in its production and application. Vermont Family Forests only recommends organic pesticide treatments. Our specific organic pesticide recommendation for EAB treatment at this point is TreeAzin or Azasol, both organic pesticides whose active ingredient, Azadirachtin, is an extract of neem tree seeds and appears to be highly successful in protecting ash trees from EAB infestation.

Azadirachtin acts by interrupting feeding and growth of EAB larvae. A report by the Canadian Forest Service (CFS) states that the active ingredient, azadirachtin, has very low toxicity to mammals, birds, and other wildlife, including soil decomposers. They do state that azadirachtin can affect (which we interpret to mean “harm”) non-target leaf-eating insects. 

Here’s how the CFS report assesses TreeAzin treatment protocol and result: 

“ TreeAzin treatments are very likely to sustain healthy, fully functional trees over extended periods of time at a cost that is equivalent to or less than that for removal and replacement of an urban tree. In the longer term, it is hoped that either natural or augmented biocontrols will be developed and become available to suppress and maintain EAB populations at less damaging levels.”

Acting together: Cost effective and empowering

This past week, David Brynn, VFF executive director and conservation forester, had three of the ash trees in his family forest inoculated with Azadirachtin (brand name Azasol), applied by Richard from Trees Vermont. You can read about his experience and thoughts about the inoculation process in his recent blog post.

Knowing that the costs associated with inoculation are high when people act alone through a commercial pesticide applicator, we’ve jumped into the process looking into the possibilities for collective action. Ash tree inoculation requires a pesticide applicators license, and our search for a local certified applicator has come up empty. Inspired by his experience of having his ash trees inoculated, David Brynn has decided to become certified in pesticide application, specifically for applying the organic EAB pesticide. 

We hope to partner with the State on research into the methods and equipment for best practices in organic treatment. The state is currently focused on “Slowing the Spread” of EAB. We’d like encourage a focus on maintaining a healthy remnant population of green, black, and white ash trees across the landscape. 

While we don’t yet have specific costs laid out, we’re hoping for less than $7 per DBH inch, which is less than half of the current commercial rate.If you have one or more ash trees you’d like to inoculate, please let us know. Springtime, as leaves bud out, is the most effective time to inoculate. Between now and next spring, we’ll be teeing up landowners interested in inoculating one or more of their ash trees.

Choosing trees to inoculate

If inoculation interests you, now is the time to determine which ash trees you’d like to treat. Here’s what to look for:

  • Health. Ash trees in excellent health, with vigorous, deep crowns, smooth bark with no nicks, not too close to roads, and not too close to the edge of forest, so as to be protected from winds. 
  • Sex. Mix of tree sexes, if possible. Ash trees are dioecious, meaning that individual trees have either male or female flowers, and that only female trees produce seeds. (Note that you may not be able to tell the sex if there are neither flowers nor seeds on your trees—ash trees don’t produce seeds every year).
  • Species. If you have black ash, consider making that a priority for inoculation. Check your forest management plan. If you have black ash in your woods, consider inoculating one or more. Beyond its ecological role, black ash has immense cultural value. Long before European settlement, Abenaki people used black ash wood for basketry. If we lose this species, we lose a remarkable indigenous tradition and skill.
Abenaki basketmaker, Aaron Wood, pounds a black ash log to loosen the wood along its growth rings for creating basket splints.

If you’d like help identifying the best trees to inoculate, we’ll walk your woods with you. By next spring, we aim have a sprinkling of small ash groves marked across the Center-West Ecoregion, ready for their first inoculation. 

Let us know if you’d like to take part!