Thyridopteryx ephemeraeformis The larval stage of the bagworm devours the foliage of junipers and many other tree species when populations of the insect are high. The larvae hatch in late May or early June and begin feeding on the juniper needles. The larva constructs a bag that covers its entire body. The worm partially emerges from its bag to feed. When the leaves are completely eaten off a branch, the bagworm moves to the next branch. By late August, the full-grown larva spins silken bands around a twig and attaches the bag permanently. In fall, the adult winged male emerges from his case, flies to a bag containing a female, mates, and dies. The black hairy male moths are sometimes seen at night around lights. The female lays 500 to 1,000 eggs before dying.

This disease is caused by one of several fungi (Gymnosporangium species) that infect both juniper and apple trees. It cannot spread from juniper to juniper, or from apple to apple, but alternates between the two. Wind-borne spores from apple leaves infect juniper needles in the summer. The fungus grows very little until the following spring, when the galls begin to form. The second spring, spores from the orange ''horns'' are carried by the wind to infect apple trees. Later, orange spots appear on the apples and upper surfaces of the leaves. In spring or summer, spores are released and carried by the wind back to junipers. The entire cycle takes 18 to 20 months on juniper plus 4 to 6 months on apple.

Carulaspis juniperi This scale is found throughout the country on many types of juniper and also on cypress (Cupressus species only) and incense cedar. The female scales spend the winter on the plant. They lay their eggs in the spring, and in midsummer (late spring in the South) the new generation, called crawlers, settles on the needles. These small (1/10 inch), soft-bodied young feed by sucking sap from the plant. The legs atrophy, and a crusty shell develops over the body. Mature female scales lay their eggs underneath the shell. Juniper scales are unable to digest fully all the sugar in the plant sap and excrete the excess in a fluid called honeydew. A sooty mold fungus may develop on the honeydew. An uncontrolled infestation of scales may kill the plant in 2 or 3 seasons.

This plant disease is caused by a fungus (Phomopsis juniperovora). It is highly destructive to junipers, cryptomeria, chamaecyparis, and arborvitae growing throughout most of the United States. The spores are spread by splashing rain, overhead watering, insects, and tools. The fungus enters through wounds or healthy tissue, killing the stem and needles above and below the point of entrance. Black spore-producing structures develop and overwinter on dead needles.

Root and crown rots on junipers are caused by several different fungi. The fungi live in the soil and on living roots. 1. Phytophthora species: These fungi cause browning and decay on the roots, and browning of the lower stems. The plants usually die slowly, but young plants may wilt and die rapidly. The disease is most prevalent in heavy, waterlogged soils. 2. Phymatotrichum omnivorum: This fungus, also known as cotton root rot or Texas root rot, is a severe problem on many plants in the Southwest. The plant often wilts and dies suddenly. Older plants may die more slowly, showing general decline and dieback symptoms. Brown strands form on the roots, and white powdery spores on the soil. The disease is most severe in heavy, alkaline soils. 3. Armillaria mellea: This disease, also known as shoestring root rot, mushroom root rot, or oak root fungus, is identified by the presence of fan-shaped plaques of white fungal strands between the bark and the wood of the roots and lower stems. This fungus grows rapidly under wet conditions. Honey-colored mushrooms appear at the base of the plant in the fall.

Oligonychus ununguis and Tetranychus urticae Spider mites, related to spiders, are among the most important pests of junipers and other evergreen trees and shrubs. They cause damage by sucking sap from the needles. As a result of their feeding, the plant''s green leaf pigment disappears, producing the stippled appearance. Spruce spider mites are more prolific in cooler weather. They feed and reproduce primarily during spring and in some cases fall. By the onset of hot weather (70°F and up), these mites have caused their maximum damage. Twospotted mites develop rapidly in hot, dry weather (70°F and up), so by midsummer they have built up to tremendous numbers.