Your arborvitae tree is dying because there is an environmental factor that is stressing the tree and causing a general decline in its health. If you suspect there is something wrong with your tree, you need to figure out what is causing the problem to be able to treat it appropriately.
The most common reasons your arborvitae tree may be dying are disease, drought, winter injury and pests.
In this article, we will discuss the different causes of a dying arborvitae tree and how to save it.
Why is my arborvitae tree dying?
One of the most common diseases that affect conifers is needle cast. This disease can spread quickly to your other trees if you do not treat it immediately. Symptoms of needle cast include dieback, excessive needle drop and chlorosis. Chlorosis is the abnormal loss of the green color in the needles.
You can treat needle cast most effectively by applying fungicide to new foliage, and anywhere symptoms have not yet appeared. Remove any affected foliage and destroy it by burning. Remember not to add this debris to compost piles. Apply fungicide to the pruned tree to protect it from infection as it recovers. Water the tree deeply once a week to support it.
Rusts is another disease, caused by fungi, and manifests as raised blisters that break open to release orange or brown spores. The color of the spores is how the disease got its name. You can tell the tree has rust when you see rust-colored powder all over the foliage and brightly-colored swellings, or galls, on the branches and twigs.
As mentioned above, apply fungicide on new foliage and on foliage where symptoms have not yet appeared. Remove all affected parts as well as any fallen debris on the ground, and burn it all.
Cercospora leaf blight is another disease that affects arborvitae. Browning will start on the lower branches near the trunk and make its way upward. The top of the tree is usually left unaffected.
Phomopsis twig blight
This disease starts at the tip of the young branches. Yellow spots will become light green and then turn brown.
Pestalotiopsis tip blight
This disease affects the ends of the branches, causing dead blotches and spots. The more the infection goes on, the closer it will move towards the base of the needles. The affected area will then become dotted with black, pimple-like structures. This infection is typically observed alongside another pathogenic infection.
Kabatina twig light
This fungal disease kills the tips of relatively young branches. There will be black, pimple-like structures where the living tissue meets the dead wood.
Drought can cause death, or at least severe damage, to the roots of the arborvitae tree. The root hairs and the feeder roots will die and will no longer be able to supply the tree with water up to the very top. Drought also makes the tree susceptible to other secondary infections or infestations.
The tricky thing about drought is that the symptoms normally do not present themselves until after a long time, sometimes even up to two years. Symptoms include a thinning canopy, dieback, cracked bark, browned needle tips, yellowing, wilting, drooping and needle drop.
You can save your afflicted arborvitae tree by removing all affected and dead foliage in order to avoid any secondary infections or infestations. Water the tree deeply once a week so that the water reaches 12 to 15 inches into the ground. If you only do light watering, the roots will grow too close to the surface and this will affect the tree’s stability. Make sure you water the tree deeply before fall ends, so that it does not suffer drought during the winter. You can also place mulch near the base of the tree to help the soil retain more moisture.
Your arborvitae might have winter burn if it starts to turn brown during the winter or early spring. This happens as a result of a combination of lack of water, too much sun, winter winds and cold temperatures. These factors all result in the plant drying out. The symptoms will appear on the tips of the branches and will progress inwards toward the center of the trunk.
You can prevent winter burn by using canvas or burlap to create barriers to protect the plant from sun and dry winds. Place stakes outside the drip line around the perimeter of the tree and wrap the material around the stakes.
Place three inches of mulch around the tree’s base. Mulching protects the roots from the cold temperature and keeps water in the soil for longer.
Deep watering is encouraged during the growing season to create a deeper root system. When trees have deeper roots, they can access moisture that is deeper in the ground.
You can also use your house as a wind barrier by planting your tree on the east or northeast side of your property.
Try to only plant arborvitae trees in the spring so that the roots get enough time to establish themselves before winter comes along and the ground freezes over.
Do not fertilize the tree in the late summer or fall. Fertilizing at this time encourages growth and may inhibit the start of dormancy.
Leafminers attack your tree by boring into the needles and feeding on them, hollowing them out from the inside.
Spider mites suck sap from the underside of the arborvitae tree’s leaves and can be very destructive. The needles will lose color and turn brown. These insects can be red, brown or black, and are about the size of a pepper grain.
The spindle-shaped cocoons of bagworms are quite difficult to tell apart from the tree’s evergreen foliage. The cocoons use twigs and needles from the tree to protect the bagworm from insecticides.
You can prevent pest damage by inspecting your tree regularly. Grow plants around the tree that naturally repel pests and insects, and make sure you keep the mulch at least three inches away from the base of the tree. Make sure you do not overwater the tree, as this can attract even more insects.
If you think your arborvitae is dying, you need to be able to identify the cause of the problem as soon as possible so that you can commence treatment immediately.
The most common causes of a dying arborvitae tree are disease, drought, winter injury and pests.
Arborvitae trees are relatively easy to care for and need very little maintenance. As long as you are able to provide their basic needs, they should have no problem thriving.
Image: istockphoto.com / Mkovalevskaya