Red oaks have shed most of their leaves now, as autumn eases towards winter.

In a Hamlin Township woods where oak wilt has killed red oaks in recent years, Forestry Assistance Program Forester and Wildlife Biologist with Manistee and Mason-Lake Conservation Districts, Joshua Shield, this fall for the second time injected 68 trees with a chemical designed to prevent oak wilt from killing them or spreading through their interconnected root system.

The trees were first injected in 2019 and will get a third round of injections in 2023. Then Shields, a Ph.D. and certified arborist and pesticide applicator as well, will wait and monitor to see if the treatment succeeds to save the trees and prevent the disease from spreading to adjacent ones.

The treated red oak surround two previously killed by oak wilt, the first in 2017.

Chemical injections to treat for oak are available from licensed applicators using pumps to force the fungicide into the tree. Current practice calls for three treatments each two years apart to treat a tree within an outbreak area to protect it.

Shield’s experiment seeks to determine if treatment using Australian-made Chemjet applicators is effective for do-it-yourself use by property owners as a less expensive means to save red oaks, the tree most susceptible to oak wilt.

Oak wilt spreads from infected trees by air transport of spores blowing in the wind or carried by picnic beetles to wounds from pruning or accidental damage to otherwise healthy oaks or through contact of intertwined roots.

An infected red oak can suddenly die and drop its leaves in mid-to-late summer or early fall. While oak wilt affects other oak species, red oak is most susceptible to dying.

“If somebody thinks they might have oak wilt, it is important to get a proper diagnosis from a professional like myself,” Shields said. “If a diagnosis shows it is in fact oak wilt, it is important to get advice from a professional who has training in oak wilt given that treatment costs for oak wilt can be quite expensive when done properly and even then, there are no guarantees that oak will not return.”

Chemjet applicators are reusable, spring-loaded plastic syringes for injecting the fungistat propiconazole into trees. Small holes, about an inch deep, are drilled at breast height every three inches around the diameter of a tree into its xylem tissue (sapwood). The applicator is pressed by hand into the tree about half inch into the sap wood. A lock is released and the spring slowly pushes so propiconazole may be taken into the tree over the course of an hour to several hours or more.

The tree’s vascular system takes up and transports the propiconazole throughout the tree moving it with water up to the canopy and down to the roots.

According to the company’s website, the reusable applicators cost about $12 to $15 each depending upon how many are purchased.

A tree ringed with injectors makes for a startling sight.

“The goal of the experiment is to test the efficacy of using a do-it-yourself injector such as Chemjet to treat oak trees that haven’t died yet that are adjacent to trees that died from oak wilt,” Shields said.

“The trees chosen were based on a scientifically-tested model called the Bruhn model.”

Johan Bruhn is a University of Missouri professor emeritus who studies and develops models and techniques for root graft barriers especially concerning oak.

The Bruhn model predicts the potential for oak wilt from an infected tree to spread through root grafts with other red oaks its roots intertwine with. All red oaks within the predicted range are considered susceptible to being infected by transfer from the infected tree’s roots.

Another oak wilt treatment option involves using a rotary plow to cut through roots to five feet of depth along the outline of the polygon surrounding an infected tree and then removing all oaks within the polygon. That had been done earlier to contain a larger outbreak in the same woods.

However, two trees in the woods hundreds of feet away later developed oak wilt presumably by air- or beetle-transport since trees in between the new and old outbreaks didn’t get oak wilt. Once in red oak, the disease is fatal.

Hamlin Township has been particularly hard hit by oak wilt, which is widespread.

“You can go to the Michigan Department of Natural Resources (DNR) oak wilt viewer to examine detections that have been reported,” Shields said.

Chemjet applications might offer a property owner seeking to save favorite trees in a yard a less expensive do-it-yourself option to save selected trees.

“Not only am I tracking the trees that have been injected, but I will monitor the site to see if oak wilt spreads underground beyond the trees that were injected and into trees outside the treatment polygon. …

“Thus far the experiment is going well. Only two trees inside the treatment area have died and they did not die from oak wilt.

“During the treatment in 2021, some trees did appear to get some phytotoxicity from the injections, but these trees will likely be just fine in 2022.”

Shields plans to examine those trees during the 2022 growing season.

Getting advice from someone with proper training is important, he said.

“Given the wide range of recommendations that landowners are given, including recommendations from those who lack proper training in oak wilt identification and management, my suggestion is that landowners communicate with a professional who has training in oak wilt. I am somebody they can reach out to.

“One very important preventative practice is to restrict pruning of susceptible oak trees to the dormant season, or at the very least not to prune from April 15th to July 15th per the Michigan DNR’s recommendations,” Shields advises.

“If pruning must take place during a risky part of the year, then applying a pruning sealer to the wound is critical to create a physical barrier between the wound and sap-feeding beetles that spread oak wilt spores aboveground.”

Joshua Shields can be contacted at 231-889-9666 or by email, joshua.shields@macd.org.

The Managing Editor for the Ludington Daily News since June 2018 and on the staff since Oct. 2011, taking over for legendary Lloyd Wallace. Previously with The Chippewa Herald in Chippewa Falls, Wis., and the Tuscola County Advertiser in Caro.

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