Rocky Mountain juniper "Wichita Blue" (Juniperus scopulorum "Wichita Blue") hails from the rugged mountain range for which it's named. Wichita blue is a tall, pyramid-shaped tree that resembles Eastern red cedar, giving rise to its nickname, Colorado red cedar. The tree's foliage is less true blue than a distinguished-looking silvery blue, making this a good choice for specimen or foundation plantings in the yard. This slow-growing cultivar is generally low maintenance and easy to grow, but it is susceptible to several diseases such as blight, canker and root rot.
Botryosphaeria Canker and Dieback
Often arising only after severe weather-related problems weaken a Wichita blue juniper, Botryosphaeria stevensii causes yellowing foliage, cankers and dieback. Spores lurk in the sunken, dark cankered areas and are spread by splashing water from heavy rainfall and overhead irrigation. Healthy trees usually do not suffer from Botryosphaeria infections. To prevent infections, water the juniper from the bottom, remove weeds and other plant debris and sanitize pruning tools and other gardening equipment before using it on the Wichita blue juniper. No fungicides are available to combat Botryosphaeria.
Wichita blue juniper is particularly susceptible to Phomopsis. Too much fertilizer is one cause of the disease, as are wet, humid weather and over-pruning the plant. Phompsis blight causes yellowing, chlorotic new shoots in the spring and early summer. As the infection spreads, the shoots die and cankers form, girdling and killing shoots and stems. The damage is mostly aesthetic, and healthy trees resist the disease. Keep trees healthy and do not over- or under-water the juniper. Avoid overhead watering, and improve drainage if water from irrigation or heavy rains stands around the base of the juniper for more than a few hours. Prune away dead areas, thinning branches and stems, if needed, to improve air circulation so the foliage dries more quickly. If the infection is severe, affecting large areas of the plant, apply a fungicide to help control the spread. Check the label to make sure the fungicide is formulated to control or prevent Phomopsis, and follow instructions for proper application timing and rates.
Kabatina Twig Blight
Often mistaken for Phompsis blight, Kabatina twig blight is best differentiated from Phomopsis by the time of year it attacks Wichita blue junipers. Kabatina infects junpers in late winter or early spring, before Phomopsis develops. Kabatina also causes the juniper to appear sickly, but the disease does not normally kill the plant. Infected shoot tips are dull green, then turn reddish or yellow before dying. Cankers may girdle the base of the shoots. The disease stops with the heat of summer. Like Phomopsis, Kabatina blight is spread by "splashing" water caused by rainfall and overhead irrigation. The fungus becomes active in cool, humid weather. Make sure the plants have good drainage and air circulation. Delay pruning chores if the weather is wet. Clean up and dispose of all weeds and plant debris during dry weather. Disturbing this material in wet weather can spread fungal spores to other parts of the yard. No fungicides are available to treat Kabatina twig blight.
Cercospora Needle Blight
Least damaging to Wichita blue juniper is Cercospora needle blight. This fungus causes the typical brown blight of the needles, beginning on the lowest branches and working its way up the tree. The fungus is most active in wet weather during the spring and summer months. Spores may be windborne or move via splashing water. Protective fungicides may be applied in mid- to late-spring to help prevent the disease. Follow product directions for proper application.
Phytophthora Root Rot
Root rot caused by Phytophthora can be lethal to Wichita blue junipers. Symptoms include yellow foliage and stunted, uneven shoot growth. As the disease spreads, entire limbs may die. The tree's feeder roots turn brittle and break easily. Rot may involve part or all of the root system. Large roots may be discolored and shed their epidermis. Remove all plant debris and improve drainage so the roots do not become waterlogged. Sanitize garden tools before using them. Amend the soil around the plant with aged bark, and correct improper pH levels. Maintain the tree's health to help it resist disease and recover more quickly if the disease strikes. If the infection is severe and other, healthy trees are at risk, consider removing the diseased juniper and replacing it with less susceptible varieties.