Infestation of Sequoia pitch moth on pine trees

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Q: How do you get rid of the infestation in pines that manifests itself as a thick white gum on the bark of the tree?

This problem is caused by an insect called the sequoia pitch moth (Synanthedon sequoiae), which is native from B.C. south to California. It tends to be a problem on certain types of pines, such as Pinus sylvestris (Scotch pine), but less on P. mugo (mugo pine).

The pest attacks pines under stress from too much or not enough moisture, depending on the species. Plants with open wounds caused by pruning, support wires, automobiles or lawnmowers are also vulnerable.

The adult moth mimics the appearance of a yellowjacket during the summer months. Eggs are laid on the bark, especially near wound sites, and the larvae burrow into the tree’s sapwood. The tree responds by exuding large masses of pitch near the entry hole. The larvae measure 24 mm (almost 1 in.) in length and are generally hairless with a pale brown head and white abdomen. The larvae will feed within the tree for a year or two. The damage to the tree is largely aesthetic, not life-threatening. New attacks occur at old sites.

Control tips:

  1. Prune in fall or early winter, October to January, so the wounds can heal before adults emerge.
  2. Minimize other stressful growing conditions, such as water shortage during prolonged periods of drought.
  3. Locate the larvae by scraping away the fresh pitch masses, and kill them.

No known chemical treatment is available.