The eastern white cedar, Thuja occidentallis, is a North American cold-weather evergreen commonly found in U.S. Hardiness Zones 6 to 2. It can survive in moderate and wet environments, but due to its inability to withstand dry conditions, it's rarely found further west than the Appalachian Mountains. This is one of the oldest species of evergreen in North America with a natural lifespan of up to 800 years. Throw in an extremely slow growth rate and shorter than average height of 50 feet once it reaches maturity, and the white cedar is popular as an ornamental tree. However, it is prone to infectious diseases.
Shoot blight is an infection caused by the fungus Pestalotiopsis funerea. This is a secondary invader that takes advantage of damage caused by frost, sunscald or broken limbs. It causes a yellow discoloration in leaves and cankers to form on twigs as it progresses from outer branches toward the white cedar's heartwood. This is normally only fatal in saplings, though it can slow growth and stress the tree. Treatment involves cutting away infected branches and applying fungicide where pruning is not feasible.
Juniper scale is a type of insect that can infest white cedar on contact and create a colony. They latch onto cones, needles and twigs and form white, button-shaped bumps between one and 1 1/2 millimeters in diameter. Each button survives by sucking the sap from its host. Over time this can stunt the tree's growth and, if the white cedar is young enough, kill it off entirely. Juniper scale is particularly difficult to kill with pesticide because the insects create a waxy outer layer that repels water-based suspensions. Instead, they can be killed by spraying them with horticultural oil, which sticks to their bodies and drowns them.
Armillaria Root Rot
Armillaria ostoyae is a species of fungus that works to break down the stumps of dead cedar trees. In this way it's a naturally occurring decomposer, but it can get out of hand. What happens is a colony of Armillaria grow into a singular mass inside a dead stump and then forms long, black tendrils called rizomorphs, which burrow up to 60 feet through the soil. Should a rizomorph touch a white cedar's root system, this becomes the point of infection, whereby the fungus moves to the living tree and begins to eat it from the inside out. If caught early enough, the infected roots can be cut away and the ground doused with fungicide, but there is no cure for Armillaria root rot once the entire root system has been compromised.