Juniper Tip Blight
Tom Creswell, Plant Disease Diagnostician, Department of Botany & Plant Pathology
Tip blights are a common problem on some juniper varieties. Two fungal pathogens, Phomopsis juniperovora and Kabatina junerperi, cause needle blighting and branch dieback. Both pathogens produce almost identical symptoms, but their disease development and control strategies differ.
Phomopsis tip blight (Figure 1) infects newly developing needles and results in 4-6 inches of branches becoming blighted. Foliage turns dull red or brown and later grey. The pathogen overwinters in the host tissue. Small, black, flask-shaped pycnidia develop at the base of affected needles and can be seen with a hand lens. Rain and irrigation disperse spores from the pycnidia throughout the year. However, infections happen whenever young foliage and high humidity are both present, most commonly in the spring and fall.
The pathogen that causes Kabatina tip blight (Figure 2) overwinters in the host tissue. The acervuli, small, black disc-shaped fungal fruiting bodies (Figures 3, 4 and 5) emerge from host tissue and release spores that are dispersed by rain and irrigation. Infection requires a wound and is often associated with insect feeding and mechanical damage. The main period for infection is in fall, although symptoms are not visible until late winter or early spring. Spread does not continue throughout the summer as is possible with Phomopsis.
Disease severity of both diseases can be reduced by several practices. Plant resistant varieties of junipers whenever possible and space properly to promote good air circulation, and lower humidity. Appropriate spring fertilization will help create strong tissue and allow plants to better defend against pathogens but avoid high nitrogen fertilizers in he late summer and fall. Irrigation should be done in early morning to allow foliage to dry faster. Infected branches should be pruned out during dry summer conditions and destroyed. However, avoid excessive pruning in spring and fall as this creates wounds used by Kabatina for infection.
Fungicide sprays are not typically needed on established plants but may be required for control of Phomopsis tip blight on young plants, or those that are highly susceptible (especially the narrow upright growing juniper varieties). Knowing when to spray depends on getting an accurate diagnosis from a lab. Treatment for Phomopsis tip blight should begin in early spring and continue at 10-14 day intervals. Spraying for Kabatina is recommended in the fall when infections occur.
Thiophanate methyl (e.g. Cleary 3336) and mancozeb (e.g. Fore, Dithane, and Protect), are registered for control of both Phomopsis and Kabatina tip blights. For information on rates of application, refer to the label.
These fact sheets have pictures and more details:
Phomopsis and Kabatina Tip Blights of Junipers - Ohio State University Extension
Juniper Tip Blights - Virginia Tech Extension, Has lists of resistant Juniper varieties.
Click image to enlarge
Figure 1. Juniper tip blight caused by Phomopsis juniperovora. Photo by David J. Moorhead, University of Georgia, Bugwood.org
Figure 2. Juniper tip blight symptoms caused by Kabatina juniperi. Photo by Cheryl Kaiser, University of Kentucky, Bugwood.org
Figure 3. Kabatina juniperi fruiting structures on juniper twig. Photo by Tom Creswell.
Figure 4. Kabatina juniperi fruiting structures on juniper twig. Photo by Tom Creswell.
Figure 5. Acervulus (fruiting structure) of Kabatina juniperi on juniper twig. Photo by Tom Creswell.