Yes, when emerald ash borer is already killing ash nearby, as it is across much of Illinois, and the tree is healthy and worth keeping, since protection works best before borers settle under the bark. Once much of the crown has died back, treatment becomes far less likely to save the tree.

Why does early treatment work better?

Because a systemic insecticide, one the tree carries through its own tissues, has to move through healthy wood to reach feeding larvae. Once borers are established, control becomes extremely difficult and damage can keep increasing even after treatment.

Which ash trees are worth protecting?

Healthy, high value ash near homes and streets. Insecticides are typically considered only for valuable trees in urban areas close to an infestation, and untreated ash in an infested area are expected to die within about 10 years.

How is a healthy ash protected preventively?

With a yearly soil drench before the beetles fly. Where a trunk injection suits trees already under attack, Once A Year Insecticidal Drench is aimed at healthy ash, mixed in water at 1 ounce per inch of trunk circumference and soaked into the soil at the base each fall or early spring.

Frequently Asked Questions

How close does the beetle need to be before treating it?

General guidance often uses about 15 miles as the point to start protecting valuable ash.

Is replacing an ash better than treating it?

For small or poorly placed ash, replacement with another species is often the practical choice.

Does untreated ash next door put a treated tree at risk?

Not directly, but they keep beetle numbers high nearby, which is why yearly protection continues.

How is crown dieback judged?

By looking for thinning foliage and dead branches in the upper canopy, compared with a healthy ash of similar size.