Globs of sap on pinyon trunk
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Issue: September 13, 1999

Globs of sap on pinyon trunk


My pinyon tree has big globs of sap on the trunk. The tree is about 15 years old and looks ok, except I am worried about the sap. A friend said that the tree has borers and is going to die. What can I do to save my tree? Albuquerque North Valley


I spoke with Bob Cain, Extension Forest Entomologist, about your problem. We agree that the problem with your tree is probably pitch moth larvae. Pitch is commonly produced by pinyon trees, but if it is in large globs, as you described, and if these pitch globs have a rosy or yellowish color, it is possible that your tree has the pitch moth. These pitch moth larvae burrow just under the bark of the pinyon stimulating the production of pitch. The moth larvae live in and eat this pitch.

Bob indicated that insecticides are not usually effective because the larvae are in the resin where insecticides do not reach them. Systemic insecticides are also ineffective because the larvae are feeding on the pitch, not the sap or the tissues of the tree. He said that most infestations require no intervention. The problem is more cosmetic than damaging. The larvae do not bore deeply into the wood or mine the cambium extensively like the bark beetle. If there is are several larvae infesting a single branch, it may be necessary to intervene and manually remove the larvae. To do this carefully dig into the pitch and look for them under the bark at the edge of the damage they have caused. Be careful as you do this, however, as you can do more damage to the tree trying to remove the insect than the insect itself was doing.

Bob also advises pruning the trees in the autumn. This is because the pitch moth is attracted to fresh wounds, such as pruning cuts, where pitch is produced. The adult pitch moth is active and laying eggs in the summer. He suggests that pruning be avoided in the summer. Spring pruning cuts may still be attractive once the moth begins egg-laying, so he doesn't recommend spring pruning. Fall pruning helps reduce the incidence of pitch moth in pinyon trees.

He also recommends that you avoid any injury to the tree, such as damage caused by bumping the tree with lawnmowers, damage caused by string trimmers, hitting the tree with vehicle doors, or even chaining pets to the tree. This will not totally eliminate pitch moth problems as some injuries to the tree are unavoidable. Wind breakage of branches, cracking of bark as the tree moves in the wind, and other such environmental injuries cannot be avoided. However, avoid all avoidable injury to the tree.