What Are Those Blobs On My Pine?

Pale yellow popcorn-like masses of sap develop as a response to Zimmerman pine moth (ZPM) larvae feeding. These caterpillars do their damage by tunneling into the trunk & branches, often causing branches to break.

Austrian & Scots pine are particularly susceptible to ZPM. Other species of pine (Mugo, red, white, Swiss stone) and occasionally spruce and Douglas fir can also be affected.

Damage is usually in the upper parts of a tree and concentrated at the branch unions. Larval feeding can also start in the shoots, leaving new growth with a shepherd’s hook appearance. With recent feeding injuries, sap is soft, with time it hardens and remains on the tree.

Adult ZPM moths are a non-descript 1 to1 ½ “gray moth with reddish brown markings. Larvae are a dirty white or gray. Adults emerge and fly in late July /August (1700 GDD) over a several week period. They mate and lay eggs near earlier ZPM wounds. Over wintering is on the bark as young caterpillars in tiny cocoons.

The caterpillars emerge in spring (25-100 GDD), mid-April to early May, and begin tunneling into the trees. Pupae remain in the feeding tunnels until adult emergence.

Mass of sap on Austrian pine is a sign of Zimmerman pine moth

Insecticide treatments are timed for early season, before tunneling begins, or later when adults are emerging and laying eggs. Applications should target the trunk area and main limbs. Insecticide sprays are only effective when the insect is exposed and on the surface of the tree. Once ZPM is inside the tree, insecticides become ineffective. There are no natural predators.

Construction damage, improper planting depth, plant injury, and drought stress all predispose trees to ZPM. Tree protection, mulching, and supplemental watering are all helpful. Consider removing heavily infested trees before July to reduce adult emergence. Needle cast diseases can also compromise tree health and appearance and should be evaluated at the same time as ZPM.

Wachtel’s Certified Arborists have years of experience in recognizing ZPM and other tree health concerns. Contact us for an on-site visit and tree assessment.

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