The Purdue Plant and Pest Diagnostic Laboratory

What's Hot at the P&PDL on
May 31, 2007

Ash Inflorescence (Flower) Galls

By Gail Ruhl, Senior Plant Disease Diagnostician, Department of Botany & Plant Pathology, Purdue Univ.

We have had several inquiries regarding bizarre looking growths in ash trees. These calls normally come in the fall when galls become more conspicuous after leaves drop from trees. However, it seems that following windy, stormy, weather these ‘strange growths” have been found ‘littering’ the ground beneath ash trees, bringing forth questions from inquiring minds. The broccoli-like growths are caused by an eriophyid mite, Eriophyes fraxinivorus, and consist of a profusion of clubby, distorted flower arts.
New galls appear as dark green clusters growing amidst current season’s leaves. Eventually, green galls turn brown-to-black and can remain attached to the twigs for two or more years. Although the galls may reduce the aesthetic appeal of heavily infested trees, they cause no injury to the tree since only the flower parts are affected.

Ash Flower Gall - University of Wisconsin Extension (pdf file)

Another image of Ash Flower Gall Mite

Click image to enlarge

Ash flower galls

Old and New Galls

Ash flower galls

Old ash flower galls from previous year

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service