Identification

• Emerald Green arborvitae is also known as American arborvitae, white cedar and eastern arborvitae from the genus Thuja. Characterized by deep green foliage and a compact shape, these evergreens are often used as specimens or hedges. Emerald Green arborvitae thrive in full sun, but also grow well in partial shade. These plants are susceptible to a variety of diseases and insect infestations that can cause serious damage to the plant or cause its death.
  
  

Insect Causes

• Spider mites are a common pest of arborvitae that cause stippling of foliage, reduced vigor and premature leaf drop. Heavy infestations of these tiny spider-like pests can cause Emerald Green arborvitae to become stunted and die. Spider mites are typically found on the undersides of foliage, where they congregate to feed. Arborvitae weevils are common pests of arborvitae that damage plants both in their larval and adult forms. Weevils are nocturnal and usually hide during the day in the soil near infested plants or in leaf litter. These small, black weevils also damage arborvitae in their larval form, which is a white grub that feeds on the roots of infested plants from June until the following spring.
  
  

Disease Causes

• Winter injury can cause your Emerald Green arborvitae to turn yellow or brown, making it appear dead or diseased. Most arborvitae turn yellow for a short time during cold weather, as well. Butt rot is perhaps the most damaging rot disease of arborvitae, affecting plants at their base, which is caused by fungi that enters the plant through wounds. Symptoms of butt rot include dieback, small leaves or needles and black fruiting bodies near the bottom of the plant. According to Iowa State University Extension, butt rot is fatal to arborvitae and there is no cure once the fungus attacks the plant.
  
  

Control

• Spider mite infestations can be removed on arborvitae by washing the plant down with a hard stream of water two or three times each week. Heavy infestations may be controlled by applying miticides to infested plants. Arborvitae weevils are best controlled with insecticides that are pyrethroid based. Apply insecticides to the foliage and cover the entire plant thoroughly for best results. There are no chemical control methods for butt rot or winter injury in Emerald Green arborvitae.