CO-Horts Blog

Saturday, August 1, 2015

Ash leaves Curling?

Posted by Eric Hammond Adams County

The wet weather which much of the state has experienced this year has been great for water bills, lawns and many plants in the garden.  However, it has also created some challenges.   One pest which has thrived under the moist and humid conditions is the ash leaf curl aphid (Prociphilus fraxinifolli).

Curling leaves on a mature ash
These insects are a type of wooly aphid which begins feeding on the underside of terminal leaves of green ash (Fraxinus pennsylvanica) in the spring.  Their feeding causes the leaves to curl (thus the aphid’s name).   Late in the summer winged individuals are produced which migrate to the roots of ash trees.

Leaves curled by ash leaf curl aphid

The damage caused by this pest is showy and often alarming to tree owners.   However, it is mostly a cosmetic issue and is normally not a serious concern to the tree’s health.   Normally treatment with insecticides is not warranted and sprays are ineffective once the leaves have curled, providing protection for the aphids within.   There are systemic treatments available but they can take several weeks or more to be affective and, again, are not normally necessary for the health of the tree.   If the curled appearance of the terminal leaves is distressing they can be removed from the tree.


Another nuisance associated with the insect is the sticky excrement they produce which is known as “honeydew”.   This sugary substance drips from affected trees in such quantity that it can coat cars, patio furniture, sidewalks or any other element of the landscape which is unlucky enough to be below the trees.   The honeydew is not only sticky and unpleasant but it is also commonly colonized by gray sooty mold which give it a black appearance with often appears to stain whatever it has dripped on.
Ash leaf curl aphids produce a white waxy substance as well as a sticky excrement
know as "Honeydew"


However, while all of this is a pain (pain in the Ash?), the issues associated with ash leaf curl aphid are still mainly aesthetic nuisances and it is not a serious threat to the tree’s health.  In most cases tolerance is the best option for dealing with the pest.   More information can be found in the “Aphid on Shade Trees and Ornimentals” Factsheet located here.


  1. Very helpful. But my tree has more serious problem. It seems to be damaged much to survive. Any one can help?