DIEBACK ornamental junipers is seen nearly every spring across Montana. Dieback of juniper is often caused by drought stress and winter freeze damage. Roots of ornamental junipers are usually only 8-10 inches beneath the soil surface, and extend several feet beyond the branches. This means they are very susceptible to drought. Because they continue to lose water through transpiration even during winter months and can not replace lost moisture in frozen ground, they can suffer drought stress even in winter.
Water these shrubs so the moisture soaks at least one foot deep several times a year, especially in late fall, just before the ground freezes, and again in spring as soon as the ground thaws. Avoid watering in late summer until time for the final watering in fall to give the shrubs time to "harden off" for winter.
JUNIPER TWIG BLIGHT is a second cause of dieback of juniper. It is a fungal disease that causes the tip of a juniper branch to die back until the whole branch is killed. Sometimes, small, black specks on foliage can be seen with a magnifying lens. If left untended, the whole shrub may die. This disease is usually a problem of seedlings and nursery stock, but it can also infect larger trees. However, shrubs and trees older than five years are usually not seriously affected.
In early spring, check for these symptoms, pruning infected branches and burning them. As with all plant diseases, when you are finished pruning, sterilize tools in a solution of one part household bleach mixed with nine parts water. Apply Benlate fungicide 3 or 4 times in spring at 2-week intervals, and once again in fall. Using a spreader-sticker solution with the benlate can increase effectiveness of the fungicide.
There are varieties of juniper which are resistant to juniper twig blight, and the whole issue can be avoided by planting these varieties. Ask your nursery or Extension agent for variety recommendations.
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Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997