Eriophyid Mite Damage on Ash
Galls on ash trees are caused by microscopic eriophyid mites. Eriophyid mites are plant-specific and usually not reason for major concern. The galls can be very unsightly, but typically do not do any serious damage. Eriophyid mite galls on flowers and buds can remain on a tree for several years before falling off. Mite galls that form on leaves can discolour or distort foliage, and even though the leaves drop in the fall, the mite infestation may return.
It is much easier to identify a gall mite infestation by the distortion of leaves and flowers, rather than by trying to find the mites. Eriophyid mites are very small, and are only visible using a microscope. The mites are worm like, and have only two pairs of legs. Males and females appear identical. They are poor crawlers and the primary method of population spread is by wind.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010