The juniper is a versatile evergreen that comes in all shapes and sizes. They are low maintenance and adapt well to less-than-perfect growing conditions. The attractive foliage of the juniper makes it a top choice among landscapers and homeowners. Juniper trees are commonly used as a hedges, for windbreaks and as background plants in gardens. Considered a fairly hardy tree, junipers are susceptible to a variety of diseases.
Phomopsis Tip Blight
Caused by the fungus Phomopsis juniperovora, phomopsis tip blight appears during warm, wet weather that occurs from mid-April until September. Phomopsis tip blight usually affects new growth and branch tips of the juniper; older foliage is resistant to infection. Infected foliage will turn red or brown and ultimately ash gray. Tiny gray lesions develop on the branch, often girdling the tips, which leads to blighting of the foliage beyond the infected area. Black fungal fruit bodies that contain spores appear in the lesions. Severe blighting causes discoloration of the foliage, stunted growth and at times the death of the juniper. Manage tip blight by trimming infected branches and twigs about 2 inches into the live, healthy wood. Destroy all infected matter. Fungicides are available to treat phomopsis tip blight.
The fungi Gymnosporangium spp. is responsible for cedar-apple rust among juniper trees and shrubs. Cedar-apple rust appears on juniper twigs and branches in the form of reddish-brown growths, better known as galls. Although size and shape of galls may vary, they are usually between 1/2 and 2 inches in diameter. Galls begin to swell and produce an orange, slimy substance that drips and oozes from the growth during April and May. Galls caused by cedar-apple rust are unsightly but pose no real danger to the health of the juniper tree. Galls are easily removed by hand during the winter months. Fungicides are effective against cedar-apple rust.
The fungus seridium unicorne is the cause seridium canker. Seridium canker often is found in trees that are suffering from environmental stresses such as drought. Wounds from pruning or injury leave the juniper vulnerable to seridium canker infection. Signs of seridium canker are long, flat cankers that begin to form on small branches and stems. Although the canker is rather shallow, it will ooze a large amount of sap. Cankers interfere with the water flow, which causes branches to wilt. Needles will turn yellow or brown and eventually fall off when touched. Severe cases of canker often result in the death of the tree. Stop the spread of canker by removing all infected branches about a foot from the canker and destroy them. Seridium canker is sometimes prevented by treating juniper trees with fungicide in the early spring months when new growth appears and again in the fall.
Cercospora Needle Blight
Repeated infections of cercospora needle blight over several years leads to defoliation or death of the juniper tree. Juniper trees that are grown in areas that experience high humidity during the summer months are more susceptible to cercospora needle blight than those grown in drier climates. Signs of cercospora needle blight begin to appear in late summer or early fall. The needles of the inner branches, those that are closest to the main tree trunk, begin to turn dull brown or red and drop from the tree. Tiny, fuzzy spore formations will appear on the dead needles. Severely infected junipers have a spindly look and sometimes take on a scorched appearance. Two applications of a liquid copper fungicide will help prevent cercospora needle blight. Apply the first dose in early June; the second spraying should take place in late July. Additional applications may be necessary during excessive periods of rain.