Issue: February 28, 2000
Black specks on needles of pinyon pineQuestion:
I have a pine tree in my yard. It's thinning - that is, there aren't a lot of needles left on it. The green needles that are left have black spots on the underside of the needles. Are these bugs? Is it killing the tree? Will this tree survive? What to do, oh my? It gets mostly morning and early afternoon sun. We just moved into the house 3 months ago from the east coast. Should I be watering the tree? Would that help?Answer:
You have described pinyon needle scale, an insect that attacks pinyon pine trees. The scale insects are debilitating for the tree but not immediately fatal. It is important to manage the problem to maintain the health of the tree.
The black spots on the needles are the waxy covering that the insect builds over itself. This covering makes chemical control difficult. According to Bob Cain, NMSU Extension Forest Entomologist, the scale insects feed by sucking the sap from the leaves. Normally, pine needles persist for several years before falling from the tree. Needles infested by pinyon needle scale turn yellow in the spring and fall earlier than they should. By reducing the number of needles remaining on the tree, the scale insects cause the thin appearance of the tree. This also reduces the number of needles producing food for the tree. According to Bob Cain, heavy infestations of pinyon needle scale can kill small trees and weaken larger trees, predisposing them to attack by other insects which may then kill the trees.
Cain explains that adult, wingless female scale insects emerge from their scale covering in mid-to-late April to mate with winged males. The females lay their yellow eggs in clusters held together by white, cottony webbing around the root collar of the trees, on the undersides of large branches, in branch crotches, or in cracks of rough bark. Sometimes the eggs are found several feet from the base of the tree on rocks or logs. It is at this time that the scale is most vulnerable to control measures. In the 5 weeks until the eggs hatch, the eggs in their cottony webbing may be removed from the tree by a broom or strong jet of water. This material with eggs may then be disposed of, removing the potential for reinfestation of the tree by the next generation of scale insects.
Cain further states that there is still a brief period during which insecticides may be effective if the egg masses are not removed before hatching. Once the eggs hatch, the scale nymphs, called crawlers, climb to the ends of branches and settle on the previous year's new growth. They insert tube-like mouth parts into the needle and cover themselves with the protective wax covering which then turns black. While the nymphs are crawling into position on the needles and until the wax is produced, the insects are exposed to chemical control.
To determine if the scale crawler nymphs are still exposed, hold a sheet of dark construction paper under the needles and. with a gloved hand, sharply strike the branch above the construction paper. Look for small insects crawling on the paper. If the nymphs are found still exposed, application of a properly labeled insecticide will help reduce the level of infestation and the damage to the tree. Repeated applications at 7 to 10 day intervals may be needed as additional eggs hatch and new crawlers move up the tree. Always remember to read and follow the label directions when using any pesticide.
Send your gardening questions to Yard and Garden, ATTN: Dr. Curtis Smith, NMSU Cooperative Extension Service, 9301 Indian School Road, NE, Suite 112, Albuquerque, NM 87112. Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.