Problems of Evergreen Trees

Some of the most commonly used evergreen trees in the landscape can be prone to insect and disease problems that can be unsightly, or even deadly. Many of these problems can be managed with timely treatment. Listed below are some of the most widespread insect and disease problems of evergreens in our area.

Spruce Spider Mite
More closely related to spiders than insects, this tiny pest causes trees to have an overall bronze or off-color cast, especially on older growth. These mites are referred to as “cool season” mites, and are most active in the spring and fall. Left unchecked, spruce mite populations can explode, causing permanent needle drop. Treatment in the spring and fall with a product registered for control of spider mites will help control these pests.

Arborvitae Leafminer
Yellow-to-brown tips on Arborvitaes often means there is an infestation of Arborvitae Leafminer, a tiny moth whose larvae tunnel into the tips of the foliage and feed inside. In late spring, you can often see the small, silvery moths congregating on infested plants. A series of treatments timed to coincide with this pest’s life cycle is in order if you suspect your plants are affected.

Scale Insects
Pines are especially susceptible to scale insects. Pine Needle Scale appears as small, white flecks on tree needles. When their populations are high, scales can cause yellowing, and a desiccated appearance to the tree. Both scales and spider mites feed on plant juices, and rob the trees of sugars they need to thrive. Treatment with horticultural oil effectively smothers scales.

Pine Needle Diseases
Two fungus diseases of pine have become common in our area in recent years. Many Austrian pines are afflicted with both diseases: Diplodia tip blight, and Red Band needle blight. Diplodia causes the newly expanding needles at the branch tips to die. Symptoms of Red Band needle blight include red to brown banding on needles, while the bases of the needles stay green. Both diseases can leave the trees very unsightly, and cause excessive needle shedding. As with other plant diseases, good sanitation is helpful- clean up fallen needles and clip out dead tips if possible. Fungicide treatments applied in the spring can help prevent spread of these diseases.

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