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Avoid trunk injections unless justified

February 19, 2019 GMT

Trunk injections are one method for treating trees for certain issues. Unfortunately, trunk injection may be used when not needed, leading to unnecessary tree damage and shortening a trees life.

Trunk injections can effectively control some pests and treat iron chlorosis if used correctly. They can also result in less pesticide being used and lowered contact of nontargets, like beneficial insects.

However, trunk injections have drawbacks. For this reason, trees should not be injected unless there is a justifiable reason for doing so. Injecting a tree is not equivalent to people receiving an injection.

Most injections are applied by drilling holes into the trunk. A healthy tree will seal or compartmentalize these wounds, but the wounds remain as dead tissue. Repeated drilling eventually creates numerous wounds that negatively impact a tree since previously used holes cannot be re-drilled and injected into.

Injection wounds opens the trunk to insect pests and decay fungi. The drilling may also break through internal barriers within the trunk the tree has made to wall off decay. Decay may then spread within the tree or from the inside out through injection wounds.

The pesticide being injected into the tree can also cause internal damage that may accumulate over years of repeated injections and potentially kill the tree, even if the pest is controlled.

When trunk injections are used for a justifiable reason, trees should not be retreated until the injection wounds close over. And remember, the wound has sealed but remains in the wood. Tree wounds do not heal like wounds on our own skin. This is why lumber has knots.

One reason for trunk injection is to treat iron chlorosis. If a tree needs treatment, the leaves will be pale green or yellow. Trunk injections are often used on pin oak and silver maple to treat for chlorosis, but unless the leaves are yellow, there is no reason to inject and create permanent wounds.

Treatment for borers is another reason to use trunk injections; but again, unless a tree has a borer issue, it should not be injected. In the case of emerald ash borer, injection is not recommended until the borer has been found within 15 miles of a tree.

In some cases, trunk injection may be the best treatment to use despite the damage it does to a tree. But do not agree to have a tree injected unless there is a justifiable reason for doing so.

If trunk injection is recommended, ask what the tree is being treated for and why trunk injection is the best choice. Ask if there are other less invasive and damaging methods to use. Ask what is being injected into the tree and what potential risks are associated with the product.

If trunk injection appears to be the best choice, make sure the person injecting the tree has experience and uses the correct equipment. For example, injection treatments that use small, shallow holes and smaller amounts of product are less damaging.

Inspect injection wounds and ask that additional trunk injections not be done until the wounds have closed completely.

Kelly Feehan is a community environment educator for Nebraska Extension-Platte County.