Issue: January 31, 2004
I was told that my piñon trees have piñon needle scale. There are many little black specks on the needles. Is this a problem? What should I do?
Piñon needle scale can be a problem. The spots are a protective covering over the scale insects. This covering protects them from the weather and many insecticides. The insects feed by drinking the sap from the needles. This insect does not kill the tree quickly; it debilitates the tree. Over time the weakened tree may die. You have probably noticed that the leaves with the black spots will turn yellow, then brown, and fall from the tree in the spring. The new leaves produced in the spring will then be infested and drop the next year. Needles should remain on the tree for several years before falling. The scale reduces the length of time the needles remain on the tree, thereby reducing the ability of the tree to feed itself.
The recent drought imposes another stress on trees and, in combination with the stress from the scale insects, may be enough to kill the tree in a few years. The recent attack of pine bark beetles associated with the drought is another threat to already debilitated trees. The answer to your question is yes, the scale is a problem, and because of the drought and bark beetles, a more eminent problem than in previous years.
The simplest thing to do is watch for the scale insects to leave their protective coverings in the late winter or early spring and migrate to the base of the tree to lay their eggs. The egg masses will look like a thick, dirty spider web or maybe like dirty, stringy yarn. This will be found under the lower branches, on the bark at the base of the tree, or on debris under the tree. By using a broom or strong blast of water, remove this egg mass from the tree so that newly hatched scale insects cannot re-infest the tree. You will not remove all the eggs, so there will be some scale remaining in the tree, but the level of infestation should be reduced enough to greatly lower the stress on the tree.
You may also use insecticides labeled for scale insects. (Acephate is often recommended.) The time to apply the insecticide is as the eggs hatch and the young, very small scale insects are climbing up the tree to infest the new leaves. You can determine when this is happening by frequent monitoring. Hold a piece of black construction paper under the lower stems and leaves, and then strike the leaves sharply with a gloved hand. Look for small insects moving on the construction paper. When you see the insects, it is time to spray the trunk, branches, and leaves. If you choose to apply an insecticide, follow the directions on the label carefully.
In some parts of New Mexico, the eggs masses may already be at the base of the trees, so start monitoring the trees now. In colder parts of the state, wait until after the eggs masses are apparent before monitoring.back to top
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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.