Jeffrey Hahn, Extension Entomologist
At this time of year, ash flower is gall particularly
conspicuous. They are black or dark brown growths found on the branches of green ash. Because of its
unsightly appearance, some people assume that it also damages trees. The good news is that does not affect the
health of ash. Research
conducted at the University of Minnesota in the 1980's showed that the presence
of galls did not impact tree health.
Control of ash flower galls is not necessary. It is also very difficult to obtain good management of these mites. If treatment is attempted, try an application of dormant oil when the mites become active in spring prior to bud break (which will occur soon), although this will only be partially effective. Ultimately the best bet is to just ignore ash flower galls. Ash has much bigger problems with emerald ash borer being present and should be considered a low maintenance tree.