1 - Piñon needle scale infestations can often be managed by removing their egg masses from the base of the tree to prevent reinfestation.

Yard and Garden April 1, 2017

Q.

I have half a dozen pinon trees that have scale and are looking rather brown and brittle. I have been watering these trees about twice a week for the last 3 weeks.

When is the best time to use a powerful water spray on these trees in order to knock off the eggs that are going to be laid by the female? After the male fertilizes them? What is a good date to do that? Also, is dormant oil a good product to use on my infested trees? If not this product, then which benign product would you suggest spraying the trees with?

- Richard R.

A.

Pinon needle scale insects are a common problem on pinon pine trees. They feed on the pinon needles with piercing / sucking mouth parts and cause the yellowing and death of the affected needles. There should be a small cluster of green, undamaged needles at the ends of the branches, while the needles just below them should have small black specks (the waxy covering created by the scale insects). It is the needles with the black specks that should be dying now. I mention this to be sure that there is not something else causing problems. This would be evident if there are not healthy green needles at the ends of the branches. These healthy green needles that formed last summer are needles that will be infested this year when the insect eggs hatch.

Your question indicates you know that the best treatment is to remove the newly deposited eggs before they hatch and produce new scale insects that will infest the green needles. The best time to do this is when you see the egg masses are deposited. In the late winter or spring (sometimes in the autumn) the female insects leave their protective coverings and migrate downward to the base of the tree to lay their already fertilized eggs. They may deposit eggs on the underside of branches, in the crevices of the bark on the trunk, around the base of the tree, in debris and mulch under the tree, and other areas near the base of the tree. The egg masses appear as dirty, stringy yarn or cotton in these locations. Removing the eggs with a broom and a strong jet of water will prevent reinfestation, or at least reduce the problem. Just washing the eggs away is not enough; the yarn-like egg masses should be collected and burned or disposed of at a distance from the pinon tree.

Timing is not critical at this stage. Your goal is to remove the egg masses before the eggs hatch to form "crawler" insects that crawl up the trunk to infest the green leaves that formed last summer. If you remove egg masses now and more appear, just remove the new masses when they appear. Timing becomes important if you try to treat the newly hatched crawler insects. Treatment must occur while the new insects are still in the crawler stage, before they attach to the needles and build their protective waxy covering. To determine the appropriate time for treating, hole a piece of white or black construction paper under the needles near the base of the tree and strike the needles with a gloved hand. Then look for very small insects moving on the paper. You can use magnifiers if you wish, but their motion should indicate their presence if they are present. Do this on a windless day so that you can find the crawlers. When you first find the crawlers actively moving up to infest the needles you can treat with horticultural oil or other products labeled for treating scale. Even when using horticultural oil and other "organic" treatments, it is important to follow the label directions very carefully. Gardeners who use less "benign" product should definitely follow all label directions exactly as presented.

If even the needles at the ends of the branches are dead and dying, there may be something else causing problems. To diagnose other problems that may be present, take samples to your local NMSU Cooperative Extension Service office.

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.

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