Evergreen – Arborvitaes

Thuja occidentalis) is a medium-sized evergreen tree native to the Northeastern United States and Canada. It has a pyramidal form, scalelike foliage and small, tan-or-brown cones. Homeowners cultivate them as windbreaks, screens and hedges. Unfortunately, arborvitae trees are susceptible to a range of disease and insect problems.
Foliage Blights

Several different diseases, such as pestalotiopsis, sclerophoma, kabatina and phomopsis, attack the foliage and cause needle or tip blight. The needles change colors, fading from green to brown, and gray lesions may form at the base depending on the fungus type. Diseased bark areas called cankers appear on the stems or trunk, while spores form on infected plant parts and spread through wind or rain infecting new trees. Water- or nutrient-stressed arborvitae are at higher risk of infection than are healthy specimens.

Sap-Sucking Pests

Arborvitae scale are immobile insects with rounded, waxy, external coverings. These pests do not resemble other insects, according to Bruce A. Barrett at the University of Missouri Extension. Homeowners often overlook them, which makes control difficult. Armored scale insects cause yellowed leaves, defoliation and dieback, while soft scales produce large amounts of a sugary liquid called honeydew. The honeydew attracts pests, such as ants and bees. A black fungus called sooty mold grows on the honeydew deposits. Aphids and spider mites drain sap from plants.

Foliage Feeders

Bagworms and leafminers attack arborvitae needles. Identify bagworms from the small bags they create from twigs and silk. Bagworm caterpillars live inside the bags and carry them around with them as they feed on the needles. Manually removing the bags controls this pest. Leafminers, which are the larvae of gray or tan moths, burrow inside the foliage and feed on the needles from inside. The needles become discolored and break easily. Prune the diseased tips for control.

Borers

Bark beetle larvae bore inside arborvitae trees creating tunnel-like galleries between the bark, causing branch dieback. Severe infestations kill stressed trees. Smaller Japanese cedar longhorned beetles are approximately 1/2 inch long, with curled antennae and bluish-gray bodies, while redcedar bark beetles are about a 1/16 inch long with black or light-brown bodies. Control infestations by drenching soil with imidacloprid and providing extra water during drought.

Read more: Arborvitae Pests & Diseases | eHow.com http://www.ehow.com/info_8778648_arborvitae-pests-diseases.html#ixzz2EsBnBZGK