A widely planted evergreen, juniper (Juniperus spp.) take many forms. They can be low-growing shrubs suitable for ground covers; small, medium or tall shrubs; or even trees. They tolerate a wide range of growing conditions including drought. Generally not bothered by pests or diseases, junipers are nevertheless bothered by several fungal diseases.
Greenish galls appear in summer and then enlarge, turning brown by autumn. Treat Cedar-apple rust by removing the galls in late winter. Monitor the plant and if necessary, remove other plants known to host this fungal disease. The alternate hosts of cedar-apple rusts include varieties of apple, pear and quince. The fungus alternates between juniper and these alternate hosts and requires the presence of both species in order to reproduce. Do not plant them near one another, or plant resistant varieties.
The fungus begins in the leaves, then moves into the twigs and finally the branches, where it causes them to die. The tips of new branches turn first brown, then gray. Twig blight is most severe in the wettest years. Keep the foliage dry, do not water in the evening and do not over fertilize. Plant and grow juniper cultivars resistant to twig blight. Treat with mancozeb, thiophanate-methyl or zyban when new growth emerges.
Cercospora Needle Blight
Symptoms appear in late summer on the needles of inner branches near the lower part of the trunk. They turn dull brown and red, eventually dropping off. Spores form on the dead needles. Defoliation continues in succeeding years, moving from the inner branches to the tips and from the bottom of the tree to the top. Applications of mancozeb in early June and in early July can help stop infection, which occurs in early summer, although symptoms do not appear until much later in the season.