Ash flower gall mite

Ash flowers may turn into brown to black cankerous masses which is caused by ash flower gall mites (Eriophyes faxiniflora). Ash trees have either male or female flowers on separate plants. The ash flower gall mite only infests male flowers. This occurs during blossom development in the spring. The tiny mites feed on the blooms resulting in the formation of galls.  The huge galls are very unsightly and can stay on the trees more than one year but do not harm the plant.

Control:

• Prune off the affected galls, preferably early in the season.

Source:

Williams, S.; Skinner, H. (2011). Gardening, naturally: A chemical-free handbook for the Prairies. Regina, Saskatchewan: Coteau Books.