This tongue twister of a pest with a passion for Fraxinus flowers has a curious life cycle.
A small mite, Eriophyes fraxiniflora can cause unsightly damage to your Ash trees.
To be clear this pest only attacks the Male flowers of the ash tree. Ash are a dioecious species, that being trees that have only male flowers on one set of individuals of the species and female flowers on the other set of individuals. Female ash trees bear copious numbers of winged seeds that can be a nuisance in the landscape. For this reason many people plant only male trees and this makes an abundance of available hosts for this pest.
The damage from this pest, twisted brown galls are most visible in the dead of winter, but the injury occurred months earlier when the trees flower in spring. The normal progression is for the flowers to fall off the tree once they have completed flowering. However as the summer progresses the distorted mite damaged flowers remain on the tree and turn into unsightly brown balls. While the trees will not be killed by this activity their twig growth will be very distorted.
The mites become active as new tissue emerges in the spring and they begin to dine on unfolding tissue. They secrete tissue distorting chemicals as they feed and the ash tree forms galls.
Control of these pests can be difficult but early season horticultural oil will provide some control if applied when buds first break. Similarly miticides applied at this time will control these pests. Ash trees flower early in spring and care must be taken to time the applications correctly.
Ash trees are currently under pressure from the potential of Emerald Ash Borer infestation and are not recommended for planting. Keeping them healthy and growing strong can help protect them from other insect infestation.
If you have questions, Certified Arborists are industry recognized experts in plant insect and diseases control. Contact your I.S.A. Certified Arborist to see if you have this damaging plant pest.