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5 Arborvitae Problems and What You Can Do About Them

Arborvitae trees are beautiful coniferous evergreens, boasting flattened, lacy, aromatic needles. They’re often used to add elegance to landscape projects and commonly appear in yards. They have a long life span and require very little maintenance. There are two commercially available cultivars: American and Japanese arborvitae.

With the prolific use of these trees in yards all over the Pacific Northwest, it’s important to know about the arborvitae problems that can occur. Let’s take a look at some of the issues that can occur with arborvitae trees:

1. Browning Leaves

The problem of browning leaves on arborvitae plants can be caused by a variety of factors, such as insufficient watering, over-fertilization, or excess or lack of sunlight.

If your arborvitae suddenly turns brown and dies, it may be caused by drought or root rot. Drought or underwatering is probably the culprit if your soil is hard and dry and your plants aren’t getting enough water. Arborvitae plants need to be watered regularly, and the soil should be kept damp at all times.

Fertilizing it too much can also lead to browning leaves on arborvitae plants.

2. Cyprus Tip Moth Miners

If a few fronds of your arborvitae tree seem to be turning yellow at the same time and then eventually go brown, it could be due to cypress tip miner moths (Argyresthia cupressella). These caterpillars are yellow or green in color and eat needles on twig tips. You should be able to remove them quickly if you shake the tree. 

Cypress tip miner moths are tiny, whitish moths that set up their cardboard-like cocoons in late summer or fall. These moths lay eggs on conifers such as Douglas firs and western red cedars in winter and early spring. Cyprus moths can be eliminated by handpicking or by cutting the branches of the trees that are infested.

3. Bagworms Infestation 

If notice little cocoon-like nests hanging off the tips of your tree branches, you might be dealing with bagworms (or Psychidae). The bagworm is one of the most common pests on arborvitae trees. While its damage might not be deadly, it can affect the appearance of your arborvitae.

The bagworm typically begins to infest a tree in early spring. It starts by laying eggs that hatch into larvae, which begin weaving together tiny, two-inch-long cones made of silk and plant matter.

Male moths emerge in late May to eat and mate. They make their nests out of leaves selected from the branches of your beautiful tree and begin to devour your trees.

If you think the problem is bad enough to stunt the tree’s growth, treat the issue with an insecticide with malathion, diazinon, or carbaryl. If you apply it to bushes or trees when the worms are still young larvae, it will kill caterpillars when they eat leaves or needles that have been treated with it. Only insects that eat the sprayed foliage are killed. You could also use Bt, or Bacillus thuringiensis, a bacteria that can be applied as soon as eggs hatch in the spring.

Before using any type of chemical on your trees, we recommend consulting with a professional tree service, such as Mr. Tree in Oregon, to ensure the safety and health of your plants.

4. Sooty Mold on Arborvitae

If you notice black, sooty mold on your arborvitae, it could be because of a scale insect infestation. Scale insects will suck sap, and nutrients, from the plant, stunting its growth and discoloring its leaves.

These little turtle-like critters are so small that at first glance, you might not notice them. Yet they can be so prolific that, if left untreated, they can eventually suffocate the tree and kill it. The easiest way to check for scale insects is by looking for brown bumps on the barks. This is a harmless fungal pathogen that grows on the insect’s excretions.

Luckily, eliminating them is easy. You can treat the issues and rid yourself of the scale insects by spraying plants thoroughly with Bugtrol and Maverik and pruning and burning the infested branches.

5. Root Rot of Arborvitae

If your arborvitae is turning reddish-brown and dying, check whether the soil is too wet. It’s best to water it in the morning so the ground has time to dry out during the day, and make sure there are no leaks or irrigation water nearby. Planting arborvitae in well-drained soil will keep them healthy.

You can get your soil tested for phytophthora root rot if you suspect an over-watering problem. Trees with root rot do not absorb sufficient water from the soil, and as a result, they wilt, appear dehydrated with thinning canopies, and slowly perish. To treat root rot in your arborvitae trees, it’s important that you use fungicides to kill off the fungus in the garden bed.

Occasionally,  root rot is so bad that organic fungicides may not be helpful. If this is the case, you must resort to chemical fungicides. If your tree already appears to be dying from root rot, there is unfortunately not much you can do to protect its health. However, you may cut a few clippings from healthy branches and propagate them.

How Can We Help?

Arborvitae trees look aesthetically pleasing, but even the hardiest trees must be cared for in the right way. If you have decided to plant arborvitae trees in your yard, you should learn the best practices to take good care of them. This will help sustain their health and make them grow beautifully.

If you need assistance with any arborvitae problems, lack the know-how to adequately care for your arborvitae trees, or just don’t have the time and would like some help, don’t worry. We are here to help. Go the extra mile to preserve your arborvitae by contacting the team at Mr. Tree Services. You’re sure to have a smooth tree care journey and great results.