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Plant NameTypeDescription 
DiebackJuniperDiseaseDieback observed on juniper is often caused by cultural or environmental factors rather than pathogenic diseases or insect infestations. Extensive foliar dieback of juniper 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.
Magnesium deficiencyJuniperDiseaseMagnesium (Mg) deficiency is a result of improper nutrition. A juniper lacking sufficient magnesium develops yellowing or dead foliage in the center and grows slowly. Older tissues are affected first. Magnesium deficiency may resemble damage caused by Phomopsis twig blight.
Pear trellis rustJuniperDiseasePear trellis rust is a fungal disease that attacks pear trees and junipers. It is commonly reported on pear leaves in western Washington. Like many rust diseases, pear trellis rust requires both hosts to complete its life cycle. Spores produced on juniper infect only pear trees and spores produced on pear only infect junipers (pear can occasionally be reinfected from overwintering diseased material on the tree). Spores produced on pears infect susceptible junipers in the fall. Infected junipers do not show symptoms until the following spring or later. Symptoms on juniper can be very difficult to detect and may include spindle-shaped swellings on twigs which girdle and kill plant tissues. The fungal fruiting structures which develop on juniper consist of long cylindrical, gelatinous, reddish-brown "horns" that appear during wet weather on the swollen tissues. Infected tissues on junipers may continue to produce spores for several years. For more information see Pear: Pear trellis rust.
Phomopsis twig blightJuniperDiseaseInfection by Phomopsis begins with young leaves at the tips of shoots and can occur any time tender young foliage is available. Initially, small yellow spots appear on the scale-like leaves. As the infection spreads, leaves die and shoots fade to light green then reddish-brown and die back. The dead twigs remain attached. Gray to black fungal fruiting bodies develop at the base of or on killed portions. Phomopsis twig blight is spread by rain and splashing water. The disease is often worse in the center of the plant where branches join the trunk, making this disease easy to confuse with magnesium deficiency.
Phytophthora root rotJuniperDiseasePhytophthora root rot is usually a problem only in areas with poor drainage or where flooding occurs. The fungus attacks the roots, which rot and die. The infection moves up into the crown, where the cambium (between the bark and the wood) turns reddish-brown or caramel in color instead of the normal creamy white. Cankers may develop near the base of older plants. The cankers are a dark reddish-brown when cut and may be accompanied by split bark and oozing pitch. Lower branches wilt and die back. Phytophthora infection spreads by water movement and contact with diseased plants or plant tissue. Foliar symptoms of Phytophthora root rot can be confused with Phomopsis twig blight and abiotic problems.
RustJuniperDiseaseSeveral types of rusts infect junipers. The alternate hosts for most of the rusts are in the rose family, including plants such as hawthorn, cotoneaster, and apple. Infected junipers develop round or elongate galls on the branches. The galls may be greenish-brown, tan, or reddish in color. Twigs above the galls may die back or may form witches' brooms. In the spring, the galls typically produce reddish fungal fruiting bodies which may appear slimy or gelatinous when wet. The fungus produces spores on the alternate hosts in mid to late summer. Pear trellis rust is also found on ornamental junipers.
AphidsJuniperInsectAphids on junipers are typically fairly large (up to 1/5" long) black insects with long legs. Aphid feeding weakens plants, causes foliage to turn brown, and may kill twigs and branches or cause premature foliage drop. The aphids often occur in large dark colonies on twigs and branches. They produce honeydew, a sweet, sticky material, and may be attended and protected by honeydew-feeding ants. Dark sooty mold may grow on the honeydew, making plants appear unhealthy.
Cypress tip mothJuniperInsectThe 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 leaves and growing shoot tips. Damage is typically limited to tips of twigs. In late winter, damaged leaves begin to turn brown. The larva exits the mined areas in late winter or early spring to make a cocoon. 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 the dead or living foliage. The adult moths appear on plants around May-June. Heavy infestations can cause severe damage.
Juniper scaleJuniperInsectThe juniper scale is a small, round, white to gray scale with a yellow dot at the center. Leaves, twigs, branches, and cones may be attacked. Symptoms of scale feeding include loss of normal color and luster of foliage, no new growth, and yellowing and death of branches. Severe infestations may kill entire plants. The scales excrete large amounts of honeydew, a sweet, sticky material, which may become covered with sooty mold. Red cedars, and Irish, Savin, and Pfitzer junipers are commonly attacked.
Juniper tip midgeJuniperInsectJuniper tip midge larvae feed in the tips of shoots, causing them to swell and form green galls. After the larvae have left, the galls turn brown (sometimes reddish) and the tips die back. Symptoms of mining and exit holes may be found at the junction between living and dead tissue or at the base of the swollen portion.
Juniper webwormJuniperInsectThe 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, then gather to feed in small colonies or nests of webbed foliage as they mature. They are yellowish to brownish with dark brown lines on the back and a dark head. The caterpillars overwinter in the nest and resume feeding in spring. Fully mature caterpillars are about 1/2" long. Due to their habit of feeding deep in the plant canopy, damage may be easily overlooked. Damaged foliage turns brown and is covered with dirty webbing.
LeafminersJuniperInsectVarious species of leafminers may occur on junipers. In general, the damage they produce is very similar to that of the cypress tip moth. Damage is typically limited to tips of twigs, which are fed upon from the inside. Damaged leaves and twigs turn brown and webbing and dark pellets of frass (excrement) may be visible. Heavy infestations can cause severe damage.
Spruce spider miteJuniperInsectFoliage of plants infested with spruce spider mites is often speckled, stippled, or bleached-looking. Severely damaged leaves or twigs may drop. Some species of spider mites produce fine webbing on the plant. They may be a problem to control because of the dense foliage typical of ornamental junipers. These mites are extremely small and are easily spread by wind, birds, and people. They overwinter as eggs on the host and can begin hatching as early as April or May.