Juniper trees are evergreen, coniferous trees or shrubs. Some are huge trees, reaching heights of 122 feet or more. Others are very short and wide and are used as ground cover, such as the creeping juniper. Some species have cedar-like, feathery foliage, while others feature sharp needles. Regardless of the species, juniper trees can suffer from the same common problems.
Blight is a blanket term used to refer to the dieback of the needles and twigs of juniper trees. The tips of the twigs and needles turn brown, and the needles eventually fall off. New shoots can shrivel up and die. If not treated, the disease spreads from the tips of the tree inward, causing the tree to die from the outermost parts in.
Blight occurs when a fungus infects the tree. The fungus is transported on water blown by the wind from tree to tree. It is especially common during warm, wet springs. There are several different types of fungi that can cause blight, including Cercospora and Phomopsis. Affected areas of the tree can be pruned off to prevent spreading, but the best way to fight the disease is to prevent it altogether with the application of a preventative fungicide in early spring.
Cedar-apple rust is a disease caused by a fungus. This disease usually moves from crab apple or apple trees to nearby juniper trees, then back again. For that reason, it is recommended that juniper trees be planted far away from any nearby apple or crab apple trees (more than two miles away).
The disease manifests on juniper trees as large galls (swollen bumps) up to 2 inches across. The galls usually appear on the ends of branches in the summer. Inside the galls, the fungus develops its spores. The galls remain on the branches until the following spring, when they burst open in the first hard rain. The orange spores then drift away on the wind to infect other nearby trees. In addition, the galls can girdle (encircle) branches of a juniper tree, causing them to die.
Galls can and should be pruned off when noticed. There are also fungicides made to specifically treat this disease.
Root rot is a common disease of many plants, including juniper trees. This disease is caused by a fungus that overwinters in the soil and feeds on the roots, rotting them away. Wet, moist soil contributes to the rise of this disease.
While there are many different fungi that can cause root rot, the most common that affects juniper trees is Phytophthora cinnamomi. There is no one obvious symptom of root rot. The tree will seem to slowly decline, with the leaves becoming sparse or dropping prematurely and the growth becoming stunted. Trees that are affected cannot be saved. Therefore, the best way to prevent root rot is to make sure the soil around your juniper tree is well-draining and that decaying organic material that can harbor fungi is raked away from the tree. In addition, if planting a new juniper, choose a variety that is known to be more resistant to root rot.