Ash leafcurl aphid—Prociphilus (=Meliarhizophagus) fraxinifolii
Feeding by this aphid (Aphididae), also named leafcurl ash aphid, causes Fraxinus spp. leaves to curl, distort, form “pseudogalls,” and drop prematurely.
The aphids are pear shaped, 1/8 inch long or less, and cover themselves with white wax. Their body is pale green or yellowish and has no distinct cornicles, a pair of tubelike projections near the hind end of the body that distinguishes most aphid species from other insects.
Several Prociphilus spp. aphids are reported on ash and they can be difficult to distinguish. The same species of aphid may look different depending on the host plant, season, and the part of the plant it is feeding on.
Ash leafcurl aphids overwinter as eggs on bark and nymphs on roots. The aphids can be abundant on leaves from spring through fall. Throughout most of the growing season, 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 and the aphids mate and disperse. They have several generations per year.
Aphid-infested ash leaves curl, distort, and drop prematurely. The aphids excrete copious honeydew and flocculent waxy material, making a mess beneath trees and promoting the growth of dark sooty mold. Abundant winged aphids can be a nuisance when they migrate between bark, foliage, or roots, especially in the fall.
Certain ash species and cultivars appear to be less susceptible to ash leafcurl aphid, but there are no research-based recommendations that identify resistant ash. The aphids apparently do not harm trees in landscapes, but their root feeding can damage small plants in nurseries.
Generally, no control is needed in landscapes to protect the survival of otherwise healthy trees. Where intolerable, they are difficult to manage without using systemic insecticide. Consult the Pest Notes: Aphids for more information.
Wax-covered aphids in curled leaves
Ash leaves curled by aphids
Aphids on roots of Fraxinus uhdei