Pests and Potential Problems

Numerous damaging agents including spider mites (Oligonychus ununguis and Eurytetranychus admes), juniper berry mites (Trisetacus quadrisetus), and red false spider mites (Pentamerismus erythreus), the latter is a potentially serious problem in shelterbelt and landscape plantings. Several true insects, butterflies and moths, flies, midges, and jumping plant lice are also pests. In nursery settings, a nematode (Pratylenchus penetrans) can injure seedlings by causing root lesions. Juniper seed chalcid (Eurytoma juniperina) attacks the seed of Rocky Mountain juniper and can cause high seed mortality. Its life cycle is currently being studied at the BPMC. (See Propagation - Fruit and Seed Collection For Details)

Rocky Mountain juniper is host to several disease organisms including Cercospora blight caused by Pseudocercospora juniperi (formerly Cercospora sequoiae var. juniperi) that can cause mortality in native stands and devastation in shelterbelts. The foliage near the base of infected branches becomes bronzed then necrotic, leaving the inner crown of the plant devoid of foliage. Phomopsis blight (Phomopsis juniperova) can also be serious, causing reduced vigor and mortality in nursery stock and recently transplanted seedlings. Infected branches turn light green then rapidly change to a red-brown color before becoming ashen gray. Kabatina tip blight of junipers (Kabatina juniperi) primarily reduces the growth and aesthetic value of Rocky Mountain juniper in the Great Plains and is currently not serious enough to warrant control in farmstead or windbreak plantings. This disease is characterized by a yellow-brown discoloration of branch tips beginning in early spring. Gymnosporangium or “cedar-apple” rusts infect both juniper and rosaceous species, these diseases need two hosts to complete their life cycle and are typically more damaging to their rosaceous hosts than to juniper. The orange, gelatinous, finger-like growths that form on the branches of junipers are common symptoms of one type of cedar-apple rust (Figure 7).

Figure 7

Damage to juniper is generally not severe but can become serious at high elevations characterized by increased moisture and concentrations of rosaceous species. Heavy infection reduces the yield, quality, vigor, and aesthetics of its rosaceous host, especially apples. Isolation of apple orchards, up to 2 miles or more, from juniper plantings is recommended. Preventative and curative fungicides can be applied to both hosts for control. Juniper can suffer serious mechanical damage from animal rubbing and reduced vigor from livestock and wildlife browsing when range conditions are poor or overstocked. Use seedling protectors and electric fence for damage prevention.

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Last Modified: 11/30/2007