Why Are My Emerald Cedar Leaves Turning Brown?

Browning on Arborvitae Branch Tips Can Be Signs of a Serious Problem

Arborvitae shrub
Kimberly Frost Photography / Getty Images

Emerald cedar arborvitae is a common tall shrub or small tree that works well for creating screens and borders. If your emerald cedar plant has leaves that turn brown, drought is usually the cause of the issue, but sometimes insects, diseases, or even dog urine can be the culprits.

Read on for the potential causes of emerald cedar arborvitae leaf browning, which is not the same as the normal shedding of its old foliage that usually occurs in the fall.

Potential Causes of Browning Leaves in Emerald Cedar Arborvitae

When you see dead foliage on the inner part of emerald cedars, it's generally not a problem. It's normal to see brown leaves in fall or spring, as emerald cedars shed old foliage. But leaves turning brown at the outer tips of branches can be serious if you see this browning pattern in the summer. Closely inspect the plants for insects or disease and investigate external factors like water and climate that can be the root cause.

Insect Activity

Several insects can cause leaf browning in arborvitae, such as aphids, spider mites, and tip miner moths.

  • Aphids: Inspect foliage closely for masses of these tiny, soft-bodied insects that can be orange, green, black, or brown. Specialized sprays are available to treat aphids, and you can also try some DIY options.
  • Spider mites: Check the tree for tiny spiders, usually red, brown, or yellow. You may also be able to see some tiny webbing. You can try using insecticidal soap on spider mites, but sometimes once they're identified, the problem is too advanced to cure.
  • Tip miners: Cypress tip miner (​Argyresthia cupressella​) moth larvae feed on the needles, turning the foliage brown. To eliminate the problem, you will need a systemic insecticide like imidacloprid or a broad-spectrum insecticide like carbaryl, according to the Agricultural and Natural Resources division of the University of California. Prune away dead or dying infected foliage.

Fungal Diseases

Stressors like being pot-bound or having too much or too little water or fertilizer can lead to fungal diseases. Spores spread by splashing water or overcrowding.

  • Blight: Look for tiny black spots on the foliage in summer. They may be caused by the fungi Phyllosticta thujae​ and ​Pestalotiopsis​. If you see them, remove infected branches to prevent further spread. If the problem persists, have your local garden center recommend an antifungal spray.
  • Rot: Crown and root rot is also caused by types of fungus, like Phytophthora​ and ​Armillaria. To prevent it, avoid overwatering and overfertilizing and plant in well-draining soil.
  • Canker: Cytospora fungus is often responsible for a canker disease. Signs of this disease include oozing from the bark, reddish-brown lesions, and sunken, soft spots in the bark. Cut away and remove affected branches. If canker disease has occurred in the main trunk, the plant will not likely recover and needs to be destroyed.

Environmental Factors

Climate issues are one of the biggest problems for most plants that are unprepared to handle temperature swings or harsh or unusual weather conditions.

  • Drought: If you inspect the brown leaves and don't see any spots or bugs, you can assume your trees are not getting enough water, so supply irrigation and use bark mulch around the trees. For established plants, a deep soaking every other week is recommended.
  • Poorly draining soil: Soggy soil can lead to root rot, crown rot, and other fungal issues. These plants prefer a well-draining loamy soil with neutral to alkaline pH.
  • Dog Urine: It can be challenging to landscape with dogs in the neighborhood. Urine spraying can be detrimental to plants. Your emerald cedar's foliage can turn brown if sprayed with dog urine. If your dog is the culprit, create a separate fenced-in area to let them run free, or opt to use a leash when taking them out. If there's a stray dog problem in your neighborhood, you can deter them from harming your plants with dog repellents.
  • Harsh winter weather: Frigid temperatures and intense winds can also cause brown arborvitae. As the temperature drops, the ground may freeze, causing the roots to freeze. The plant may dry out if the roots can't take in water. If the sun still hits the tree and it's dry, it can cause leaf browning when a plant is not wrapped or protected against intense weather.

Is Your Emerald Cedar Plant Salvageable?

If the plant has been damaged by drought, root damage can occur, which can eventually lead to dead plants. To check if your plant is dead or still alive, slice off a bit of bark with a knife. If you see green, the plant is probably living.

The plant has died if all you see is brown under the bark. It may take a few tries on a partially dead plant before you find green somewhere. It should be removed and destroyed (and not composted) if you suspect fungal disease or a bad insect infestation.

Sometimes, a branch that has turned brown will regrow with the coming of the spring season. Prune it in the spring just as the temperatures start to rise again. However, if the majority of the tree has browned, it might not recover. After you give it a chance to rebound throughout the spring season, and you haven't seen any significant changes, plan on tree removal.

Article Sources
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  1. Emerald Green Arborvitae. University of Washington Website