Leafcurl ash aphid

Description of leafcurl ash aphid

The leafcurl ash aphid (Prociphilus fraxinifolii) is a consistent pest of green ash trees. Leafcurl ash aphids are small light-green insects covered with off-white waxy threads.  They remain on the underside of the leaves, inside the curled leaves.  Biological controls, especially syrphid fly larvae and lady beetle larvae are often abundant among the aphids.

Damage caused by leafcurl ash aphid

Presence of the aphids on the undersides of the foliage causes a distinctive gnarled deformation at the ends of the twigs.  The clusters of tightly coiled leaflets are noticeable throughout the second half of the summer.  Damage is annoying and aesthetically displeasing but has no significant impact on otherwise healthy trees. 

Damage occurs only on new growth that emerges after the aphids arrive in mid to late May.  Expanded leaves are not susceptible to leaf curling.  Consequently, the damage remains confined to a very limited proportion of the tree’s total foliage.

Management of leafcurl ash aphid

Spraying insecticides is generally not warranted for this problem.  By the time damage is apparent it is too late for effective treatment.  Spraying would have to precede deformation, as curled leaves will not return to normal even if the aphids are killed.  Damage is aesthetic and of no consequence on healthy, well-established trees and spraying will be harmful to biological controls.  If preventive chemical treatment can be justified use a foliar systemic insecticide such as Orthene or Dimethoate.

As a practical consideration, prune off and discard the deformed terminals that can be reached and ignore the rest.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

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Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 13, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.