April 18, 2015

1 - PiƱon needle scale is a common insect problem that may be treated with insecticides or by non-chemical methods.

Yard and Garden April 18, 2015

Q.

Our piñon trees are infested with scale (little black specks turning the needles yellow). What can we do to save them?

-Sylvia R.

Via University-Wide Extension web site

A.

Your piñon trees have a common pest of piñon, the piñon needle scale. They rarely kill piñon trees quickly, but make them weak and susceptible to other problems such as attack by borer insects and drought. These small insects cause slow debilitation of trees by reducing the number of functional needles on the trees. With fewer needles to capture sunlight and feed the tree through photosynthesis, the trees become weaker over time.

The black specks you described on the needles are a waxy material the insect makes to cover itself for protection. This waxy "house" protects the insects from drying and from some predators. The yellowing needles you described are the symptoms of their feeding on the needles. You will notice that there is a tuft of green needles at the ends of the twigs with a cluster of yellowed needles immediately behind the green needles, and usually no needles on the twigs after that. The green needles are needles that formed last year after the scale had infested the needles formed the previous year. These infested needles will fall from the twigs this year and the needles that formed last year will become infested this year. A small tuft of new needles will form this year and maintain the appearance described above.

The adult needle scale insects usually leave their protective coverings in late winter and migrate down the tree. The female insects then lay their eggs on the underside of branches, on the trunk, and in debris at the base of the tree. A simple and effective way to reduce the effect of piñon needle scale on your tree is to remove the eggs from the tree. The eggs are contained in a dirty-white material that looks much like strands of yarn or very think spider webbing on the underside of branches, the trunk, and the debris. Using a broom to sweep most of this material from the tree or a strong jet of water to wash it away removes the eggs and reduces the infestation of the new needles as they form. If you can collect the egg masses and destroy them, then there will be few new insects to infest the needles that form this year.

If you want to have an even greater impact on the piñon needle scale infestation you can watch for the newly hatched insects moving back up the tree to settle down on the green needles that formed last year. These "crawler" phase insects are very small and most easily detected by holding a black or light colored piece of construction paper below the needles. Then you can sharply strike the branch and needles above the paper with a gloved hand (gloved to protect you from needles punctures). If you see very small specks moving around on the paper after this test you have discovered the crawlers. If you wish you may then spray the tree (on a windless day) with insecticides labeled to control scale on ornamental conifers. An insecticide containing the active ingredient acephate™ is often effective when the crawlers are present. This is not an organic material and if the eggs were sufficiently removed, treatment with insecticide will not be essential. If you missed removing the eggs before they hatched chemical treatment may be the only way to manage the problem this year. However, since this insect is unlikely to kill the tree quickly, you can wait and remove the egg masses as soon as they appear next year if you prefer not to use chemicals.

An interesting note about this insect is that although they normally leave their protective covering to deposit their eggs in the late winter, they were observed out of the coverings and laying eggs in the autumn last year in Santa Fe. So, egg mass removal can begin earlier in some years.

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, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!