Diseases of the Mugo Pine

An evergreen plant, the mugo pine (Pinus mugo) produces dark-green needles. Its various cultivars come in sizes between 15 and 20 feet in height when mature. It grows well in U.S. Department of Agriculture plant hardiness zones 3 to 7, especially when it receives plenty of sun and moisture in the soil. The mugo pine suffers from several fungal diseases.

The fungus Sphaeropsis sapinea attacks mature mugo pines that are at least 12 years of age. It usually attacks in the spring, but may worsen in mid- to late summer and fall. The disease stunts new needle growth, turning them brown, twisting and eventually killing them. Older needles also die as the disease progresses. A small, black fungus appears at the needles’ base. This disease weakens and kills infected mugo pines in time.

Also known as red band needle blight, the fungus Dosthistroma septospora causes dothistroma needle blight. The disease usually appears in early the fall, starting at the tree’s lower parts. It forms bands around needles, first appearing dark green and later turning brown or red. The tips of infected needles die, but their bases remain green. The infected parts may bend down or fall off. In the fall, black spots appear on these dead tips.

Pine-oak gall rust or Eastern gall rust causes swellings, galls, on the stems and branches. Each gall may measure up to 10 inches in diameter. In the summer, yellow or orange powders appear on the galls. These powders are the spores of the fungus. The fungus (Cronartium quercuum) then moves to a host of the oak family, causing rusty spots to appear on the leaves.

Removing infected parts with the discoloration or galls minimizes damage. This reduces the spread rate of the disease. Fungicides also help control these diseases. Regular spraying of preventative fungicides works well with tip blight and needle blight. Use the appropriate fungicide to spray the mugo pine twice a year for needle blight or three times a year for tip blight. For pine-oak gall rust, only apply a fungicide containing mancozeb when yellow blisters appear on the galls.