Junipers are large shrubs or small trees that are prized for their ease of care in the home garden. However, junipers are susceptible to disease problems that may cause cosmetic damage to severe injury. Identify proper care for vigorous plants ready to fight disease. Familiarize yourself with juniper diseases and control methods for continued plant health.
Junipers (Juniperus species) are less likely to suffer from disease when vigorous compared to weakened or stressed plants that are more often attacked. All species thrive in locations that provide full sun exposure and prefer well-drained soil, according to the Clemson University Extension. Though you may plant juniper shrubs in a wide variety of soil types, avoid excessively wet sites to prevent fungal infections.
Junipers are most often infected by fungal diseases, including blight and rust problems. Phomopsis tip blight, for example, is caused by the fungus Phomopsis juniperovora. The fungi invade branch tips, infecting new growth, according to the Clemson University Extension. Cedar-apple rust is another common disease of juniper shrubs, caused by a variety of species of the fungus Gymnosporangium. This fungus needs two host plants for a complete cycle, including one juniper shrub and one apple tree.
Symptoms and Damage
Phomopsis tip blight results in mature foliage that remains healthy but immature foliage that falls ill. Twigs fade to a lighter color and transition into a red-brown until after death, when the entire twig displays a solid brown hue, according to the Clemson University Extension. Cedar-apple rust begins on the juniper shrub, moves to the apple host, and returns to the juniper during its cycle. On the juniper, look for raised brown areas called galls; measuring approximately 2 inches across, these hard growths develop on the outermost portion of juniper branches. Damage may become severe if left untreated.
For disease, one of the best preventive control methods is planting resistant varieties. Though not immune, resistant varieties are much more likely to avoid infection than other junipers. Varieties resistant to phomopsis blight and apple-cedar rust include, but are not limited to, the Chinese juniper (Juniperus chinensis) varieties Keteleeri and Mint Julep. Common juniper (J. communis) variety Aureospica is resistant as well as Eastern red cedar (J. virginiana) Tripartita, according to the Clemson University Extension.
For control of phomopsis tip blight, remove and destroy infected plant parts. If pruning is unsuccessful, utilize a chemical control method. The fungicides including the active ingredient mancozeb or copper salts are effective for this fungal infection. For cedar-apple rust, avoid planting highly susceptible junipers near susceptible apple trees; resistant apple varieties include Pristine and Liberty. Remove galls from the juniper and sanitize your shears between each cut and before you move on to another plant. For severe infection, apply a fungicide with the active ingredient mancozeb or triadimefon, according to the Clemson University Extension.