Homegrown: Sick juniper tree
We have native juniper tree in our yard that is looking sick. The tree has a good sized limb that died. When you look closer, part of the dead limb has small bore holes, probably from some sort of beetle, I’d guess. The other limbs aren’t showing many bore holes (yet) but they seem to be a bit stressed. The tree is right out in the front of our house next to the driveway, so we’d like to save it if we can. What would you recommend? — George
You have some sort of engraver beetle working on your juniper, probably the western cedar bark beetle.
The adults are dark brown to black beetles and quite small, typically no more than 1/8-inch long.
The adults do some minor feeding on the green ends of branches causing some brown tips to the growth. This damage is unimportant to the overall health of the tree.
The significant damage this insect does is when the female constructs a brood tunnel. She bores into the trunk or branches an inch or more in diameter and excavates a tunnel that runs vertically, along the length of the branch. She will then lay numerous eggs along its length. When the young larva hatch out, they tunnel away from the brood tunnel at a right angle.
This tunneling activity is a major disruption to the vascular system of that stem, usually leading to its death.
The most important thing to remember with this beetle is that it is a relatively nonaggressive pest and is only attracted to plants that are under stress. The best prevention for this insect is to maintain your plants in a healthy and vigorous condition.
Our common native juniper is the singleseed juniper. If this was an existing native tree and you built around it, it is not uncommon for these trees to be stressed because of the construction activity nearby.
Believe it or not, these sorts of issues can appear years after the construction work was done. Those junipers have roots that go forever and I’m sure that there was some damage done. This isn’t the end of the world. It’s just something of which to be aware.
First, make sure that you are doing all you can to make the tree as happy and healthy as you can. Water it deeply but allow the soil to dry out significantly before soaking it again.
This juniper doesn’t like “wet feet” and keeping it too damp will lead to problems.
If the juniper was planted after the house was constructed, this still applies, just not to the degree that I outlined before.
In addition to this, there are some things you can be actively doing to help the plant.
First, cut off all the dead growth and dispose of it. Don’t leave the cut branches lying around the yard as the beetles will continue to feed in them and pose a threat to the junipers around. The cut branches can be burned, chipped up, or simply left in the trash for the garbage truck to haul away.
You can also apply some insecticide sprays to help protect the tree. You’re a little late getting started, but get going on it right away.
Apply a spray of 38 percent Permethrin mixed with water according to label directions. Thoroughly cover the bark of all branches 1 inch in diameter or bigger as well as the tips of the growth. I suggest you repeat the spray in about a month.
Next year, start spraying the first of July and repeat the first of August and again the first of September. Plan on doing this for the next three or four years until the tree has a chance to get back on its feet.
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