Junipers (species Juniperus) are coniferous evergreens with prickly, needle-like foliage. They are desirable for their ease of care and because they can survive and thrive in a wide range of conditions. Most junipers are also pest- and disease-resistant. There are hundreds of types of junipers, from creeping juniper, which is often used as a ground cover or to control erosion, to towering trees. Junipers are classified as either spreading or upright. Although hardy, they can suffer from diseases.
Lesion Nematode Disease
Several types of junipers are very susceptible to lesion nematodes (Praytlenchus vulnus), according to R. K. Jones, a plant pathologist with the University of North Carolina. Damage occurs gradually, starting with the juniper beginning to show yellowing of the foliage, followed by poor growth and then wilting. Eventually, the foliage will drop off and the shrub or tree will experience dieback, which is when the plant begins to die from the outer tips of the branches inward. Most junipers take several years to die from the disease. There is no chemical way to control or prevent the disease.
Phytophthora Root Rot
Phytophthora root rot is a disease caused by a fungus called Phytophthora cinnamomi. This disease causes the juniper to slowly decline and eventually die. The foliage over the entire plant may become thin and drop off. In other cases, large parts of the juniper die suddenly. Phytophthora root rot is difficult to contain or control because it can lie dormant in the soil for a long time before attacking the plant. It also spreads quickly through water runoff. There are no chemical means of curing this disease.
Cercospora Twig Blight
This fungal disease (Cercospora Sequoiae var. Juniperi) infects the needles of the juniper rather than the roots. It is transmitted on water, often splashing rain, and usually attacks during warm, wet springs. The disease begins in the lower, inner branches of the juniper, turning them brown. Over time, the browning spreads throughout the rest of the juniper. Sometimes the infected needles drop, but the still-green needles on the tips of the branches remain, giving the plant a strange, thin appearance. Once affected, trees cannot be cured, but a preventative application of fungicide applied in the spring can prevent the disease from taking hold of the juniper.