Ash Leaf Curl Aphid in the yard?

Courtesy of the CSU Extension Office

    If your ash tree is looking strange and the leaves are twisted, puckered and curled on the ends, pick a few leaves and open them up.   You may find hundreds of leaf-curl aphids along with an abundance of white waxy material they produce.
    These aphids feed by sucking the sap from the plant through a hypodermic needle-like stylet.  Aphids have little need for the sugar the sap contains, so it’s excreted as sweet, sticky honeydew that may attract ants.  Furniture and cars under a tree are often varnished by the honeydew.  Surfaces may also be covered with a black fungus called sooty mold. This mold grows on the honeydew produced by the aphid.
    Aphids have many predators, but manage to survive by having lots of offspring – quickly at certain times of the year.  All aphids are born female, and they’re born pregnant.  It’s called parthenogenesis.  Because they mature in about a week and can have more than 100 offspring each, large populations build up quickly.  
    Even though the damage looks significant, infestations generally do little harm.  The leaves can still photosynthesize, and those that are distorted will not be improved with a pesticide spray.  A healthy tree is able to withstand considerable leaf damage, and it’s unlikely that we have the same problem every year.   There seems to be a range in susceptibility among ash cultivars to damage by this insect with some (e.g. Patmore) being more commonly damaged.  By midsummer, several natural controls typically curtain outbreaks, particularly after succulent new growth is no longer being produced.  Earwigs, syphidfly larvae and parasitic wasps are among the most commonly observed biological controls. 
Systemic insecticides have been the only effective treatment identified for this insect, and they need to be applied to the soil.
    For information on leaf curling aphids or other garden questions, contact the CSU Extension Office in Adams County at 303-637-8100.