Poplar Petiole Gall Aphids

Look for hard, pale green swellings along the leaf petioles or midribs of black cottonwood and trembling aspen in the Puget Sound region; mature galls appear rounded and tightly enclose small grayish, waxy aphids inside. These galls develop in early summer as aphids feed on petiole tissues, with damage mostly cosmetic on poplars themselves. The pests are distinguishable by short antennae and undeveloped cornicles.

Poplar petiole gall aphids migrate to herbaceous hosts like lettuce and beet in midsummer where they cause root damage. Focus monitoring on summer vegetable hosts if grown nearby. Remove heavily infested leaves, or tolerate minor cosmetic damage on ornamental poplars. Chemical intervention is seldom needed for this pest.