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Plant NameTypeDescription 
Berckmann's blightArborvitaeDiseaseBerckmann's blight is a fungal disease of the leaves and small twigs of Oriental arborvitae. Growth at the tips of branches is infected first, turning brown in late spring. As the infection moves down the branch, foliage becomes grayish. Branchlets and twigs may be girdled and die back, with foliage above the dieback turning reddish-brown. Tiny black fruiting bodies of the fungus may be present on infected foliage and where twigs are girdled. Infected foliage drops from the plant. The fungus overwinters on infected tissues and can be spread by splashing water, insects, or air movement. Repeated severe defoliation will eventually kill plants.
Cedar flaggingArborvitaeDiseaseEvergreen plants naturally shed some old foliage each year. Stress factors, such as lack of sufficient water, hot winds, construction damage or other root disturbance, poor planting procedures, or recent planting can promote flagging. Brown foliage develops on the tree or shrub in mid- to late summer and is very obvious by early fall. The affected foliage consists of older growth formed in previous years. Foliage developed during the current year (at the branch tips) remains green. These brown branchlets are called flags and are generally spread uniformly throughout the canopy. Affected foliage may begin to drop during hot, dry weather. Most of the dead foliage is blown out of the plant by the wind in fall and winter, and the plant typically resumes its healthy appearance.
Leaf blightArborvitaeDiseaseLeaf blight is a fungal disease. The symptoms typically appear first in late spring as bleached spots followed by brown or black cushion-like fungal fruiting bodies. Infected foliage may be anywhere on the plant. Individual leaves are killed by the fungus and turn a light tan to gray color. As the fruiting bodies drop out of the leaves, deep pits are left in the dead tissue. The infected tissues often have a "scorched" appearance. Infected leaves often drop in the fall. Western red cedar (Thuja plicata) is most commonly infected, particularly the cultivars 'Atrovirens' and 'Excelsa'. A similar disease attacks junipers.
Shoot tip diebackArborvitaeDiseaseDieback observed on arborvitae is often caused by cultural or environmental factors rather than pathogenic diseases or insect infestations. Extensive foliar dieback of arborvitae suggests that the site is less than optimal for the growth of these plants. They require excellent soil drainage as well as air circulation around the foliage in order to thrive. When soils are saturated, roots become rotten and are unable to absorb sufficient water and nutrients for healthy plant growth. Poor foliar color and dieback often occur as a response to this limited uptake of water and nutrients. Excessive moisture on the foliage can promote dieback and can aggravate other problems.
Twig blightArborvitaeDiseaseTwig blight is a fungal disease of the leaves and shoots. Young leaves at the tips of shoots are infected first. This can occur any time tender young foliage is available. As the infection spreads down the shoots, leaves die and shoots turn dull red-brown. Branch tips are often girdled, with small gray lesions at the point of infection. Dead twigs turn gray and remain attached to the plant. Black fungal fruiting bodies develop on the girdling lesions. This disease is favored by moist conditions such as high humidity and damp foliage. The fungus can survive in killed tissues. This disease also infects junipers.
Cypress tip mothArborvitaeInsectThe adult cypress tip moth (cypress tip miner) is a silver-tan moth approximately 1/4" in length. The larvae are green, about 1/8" long, and tunnel in the one- and two-year-old shoot tips. Damage is typically limited to tips of twigs. In late winter, damaged tips begin to turn brown. The larvae exit the mined areas in late winter or early spring to make cocoons. The exit holes are dark and may resemble symptoms of leaf blight, a fungal disease. The cocoon is a white, somewhat papery structure made in dead or living foliage. The adult moths appear on plants around May-June. Repeated heavy infestations can cause severe damage. Junipers are also infested.
Flat-headed and shothole borersArborvitaeInsectFlat-headed borer attacks are most severe on declining plants. The 1/2" adults are either brown to metallic gray or black with red or orange markings, depending on species. The larvae mine under bark and may girdle plants. Weeping sap, depressions in the bark, and split bark are symptoms of feeding. Shothole borers are primarily a concern on weakened or declining plants. The adults are small (1/10"), red-brown to black beetles. They feed on twig tips of healthy plants, mining the terminal portions for about 6". Damaged tips die back, producing symptoms of flagging which may be conspicuous in ornamentals. The larvae (bark beetles) feed beneath the bark on the trunk, leaving characteristic "shothole" symptoms (tiny holes in the bark) when they emerge. Larval feeding may also be associated with weeping sap on the trunk.
Juniper scaleArborvitaeInsectJuniper scale is a small, round, white to gray scale with a yellow dot at the center. Leaves, twigs and branches may be attacked. Symptoms of scale feeding include loss of normal color and luster of foliage, lack of new growth, and yellowing and death of branches. Severe infestations are rare, but may kill plants. The scales excrete large amounts of honeydew, a sweet, sticky material. Honeydew may attract ants, or may become covered with a growth of dark sooty mold. Red cedars and Pfitzer, Irish, and Savin junipers are also commonly attacked.
Juniper webwormArborvitaeInsectThe adult juniper webworm is a copper-brown moth with white bands on the edges of the front wings. The moth is about 1/2" across. The webworm caterpillars initially feed by mining inside leaves. As they mature, they gather to feed in small colonies or nests of webbed foliage. The dark-headed caterpillars are yellowish to brown with dark brown lines on the back. They overwinter in the nest and resume feeding in the spring. Fully mature caterpillars are about 1/2" long. Damaged foliage turns brown and is covered with dirty webbing. Due to the caterpillars' habit of feeding deep in the plant canopy, damage may be easily overlooked.
LeafminersArborvitaeInsectVarious species of leafminers may attack arborvitae. In general, leafminer damage is very similar to that of the cypress tip moth. Damage is typically limited to tips of twigs, where leaves and twigs are fed upon from the inside by small larvae. Damaged leaves and twigs turn brown. Webbing and dark pellets of frass (excrement) may be visible. Heavy infestations can cause severe damage. Similar damage from leafminers may also be seen on junipers.
Spider mitesArborvitaeInsectSpider mites are tiny, eight-legged, and of various colors from yellowish or greenish to red. They may be found on the foliage and often produce a fine webbing on the branchlets or between twigs. Spider mite feeding results in a very fine yellowish speckling or stippling on the foliage, causing plants to appear discolored and unhealthy. Severe infestations cause leaves to turn brown and may weaken plants. Spider mite infestations are often worse during dry, dusty conditions.
Spruce bud scaleArborvitaeInsectSpruce bud scales are shiny brown insects found on the twigs. Heavily infested plants may appear yellowish or show other signs of stress. New growth may be stunted or lacking. Adults are 1/8"-1/4" in diameter and roughly turtle-shaped. Crawlers (immature scales) are flatter. Scales produce large amounts of honeydew, a sweet, sticky material which may attract ants or become covered with a growth of dark sooty mold. Spruce bud scale is a common pest in the landscape, infesting spruce and pine as well as arborvitae.