How to tell if your trees are healthy

In the fall people worry that their pine, spruce, cedar (conifer) trees are diseased or infested with insects. The symptoms that are described on their trees include yellowing and dropping of older needles. In fact, most callers stress that only the tips of branches are still green, while on the insides of branches, needles are browning and dropping to the ground.

Fortunately, what they are seeing are not disease or insect pests. The good news is that fall drop of older needles is normal. Pines and other conifers such as spruce and fir get ready for winter each fall by shedding some of their older, less efficient needles. Since conifers are "evergreen" and thus retain their needles over the winter, they must provide water and food (in the form of stored sugars) for these needles. But winters can be cold and dark in our part of the world, so conifers have evolved a way to support only the needles they can depend on for the best solar collection and energy production. The least efficient needles are the shaded ones on the insides of branches. The needles that are most effective at capturing the sun's energy are the youngest, unshaded needles at the tips of branches. So, conifers shed their most inefficient needles in the fall before they have to support them through a long winter.

This may sound a bit ruthless, but it is normal. The conifers we call "evergreen" usually hold on to their needles for only about three to seven years. They look evergreen because they never shed all their needles at once, only the oldest ones. Healthy, vigorous pine trees hold on to the less inefficient needles longer than drought-stressed or insect-attacked trees.

How do you know if the brown or yellow dropping needles on your pine tree are okay or not? Check the buds at the ends of branches. These will form the new growth next year. If these buds are green, fat and sticky now, and the needles at the ends of branches are green, your tree is probably fine. If the needles that grew this year at the ends of branches are yellow or brown and the buds at the very tips of branches are shriveled or brown inside, your evergreen may be affected by insects or disease.

For more information on tree insects and diseases contact your local county extension agent or your can go to the Missoula County Extension Service plant diagnostic database at missoulaeduplace.org and click on Plant Clinic to see photos of tree insect and disease pests.