Protect your trees: Tips on avoiding damage from invasive insect pests this spring


By Sarah Hanson

Guess what time it is? It is time to protect your ash trees.

The emerald ash borer (EAB) insect has been confirmed in just about every Indiana county, including Brown, Johnson and Shelby counties nearby. To see a map of where the insect has been confirmed in Indiana, go online at

Let’s clear up the rumors: This invasive pest was not killed by the cold winter. Experts still are advising everyone to move forward with a management plan. Here are a few quick background facts:

  • EAB kills 99.9 percent of the untreated ash trees it attacks
  • The adult is a shiny green, winged insect that fits on a penny
  • The worm-like larvae hatch in July and feed under tree bark all summer
  • Early signs of EAB infestation include a thinned tree canopy, woodpecker damage and bark splitting
  • Later signs of infestation include branch dieback in upper third of tree and sprouts that appear at the trunk
  • The best insecticides for saving your ash trees contain imidacloprid and should be applied before June

If ash trees are not important to your landscape, planted in a poor site or show many outward signs of infestation, then saving it may not be your plan.

However, healthy ash trees that you want to keep can be protected by using insecticides. If more than 50 percent of the tree’s leaf canopy still is there, then the tree can usually be saved. Most treatments should be applied between April 1 and May 15 so that the tree can circulate the insecticides throughout all its branches and leaves. The systemic insecticides used for EAB control will impact other insect species that feed on treated ash trees, but ash trees that aren’t protected with treatment will be killed by EAB (which also impacts these insects).

Ash trees are wind-pollinated and aren’t a nectar source for bees. Ash flowers are produced early in the growing season and are present for only a limited number of days. The likelihood of bees being exposed to systemic insecticides via an ash tree is low.

If you invest in insecticides over the next few years, it can pay off. Remember that having a tree in your yard provides benefits such as adding value to property, increasing air quality, intercepting stormwater runoff, reducing soil erosion, blocking wind, providing shade, etc. Depending on the insecticide chemicals used, trees will need treatment every one to two years.

Spending money to prevent your ash trees from being infested truly is an investment. Some insecticides can be bought and applied by a homeowner. However, if you measure a tree trunk diameter at about 4.5 feet from the ground and it’s over 20 inches, you will need to hire a professional.

A local Purdue Extension office can give you a list of local tree care companies, and you can find tree care professionals online at

It is even possible to talk with neighbors or your homeowners association about getting a group rate on professional tree services. Also, if your neighborhood is interested in an educational program, I or another Purdue Extension educator can come out and do that.

Huge amounts of other great information are on the previously mentioned website as well. You can even use a “cost calculator” to determine your options for treating a tree versus taking it down and replacing it. Remember to plant a diverse mix of trees to increase resiliency to future pest problems.

Sarah Hanson is the Purdue Extension Johnson County director and the agriculture and natural resources educator. Send comments to [email protected].

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