Manzanita leafgall aphid—Tamalia coweni
The manzanita leafgall aphid (Aphididae) causes leaves to swell into pod-shaped galls. At least one other species of aphid, Tamalia dicksoni, causes similar galls on the leaves of Arctostaphylos spp. shrubs. Heavily infested plants may grow slowly, but the galling is otherwise harmless to manzanita.
Feeding by Tamalia spp. causes green or red, elongate to pod-shaped galls on Arctostaphylos leaves. Galled leaves commonly appear to have swollen or rolled leaf edges. Tiny, gray or greenish aphids feed by sucking on tissue within the leaf galls.
These aphids feed only on manzanita. Throughout most of the year adult females (which may be winged or wingless) give birth to live young without mating. In the fall, a sexual generation of winged males and females is produced. The winged aphids disperse, mate, and the females lay overwintering eggs on bark at the base of the plant. Eggs hatch in late winter or spring and the emerging aphids walk up to the leaves, settle to feed, and initiate galls. They have several generations per year.
The aphid causes pod-shaped, green to reddish galls in manzanita leaves. The damage does not significantly affect plant health, but can be aesthetically objectionable.
Manzanita leafgall aphids are prevalent on new growth, such as that stimulated by frequently irrigating and shearing plants. Avoid fertilization and minimize pruning and other cultural practices that stimulate succulent plant growth. Do not irrigate too frequently or with excess amounts. Avoid applying nitrogen fertilizers to established plants. If fertilizing, apply no more than necessary and use slow-release materials to avoid stimulating aphid populations.
If these aphids were not tolerable the previous season, horticultural oil can be applied to lower trunk bark when buds begin to swell but before they burst into new leaves. Oil application may be a good choice if plants are also infested by scale insects or other pests overwintering on bark that will also be controlled.
Certain systemic insecticides can be effective if applied before leaves become galled, but may kill bees and natural enemies that feed on plant nectar and pollen. Consult the Pest Notes: Aphids for more information.