Ash Flower Gall Midge

Ash trees are known for smaller, inconspicuous flowers. If you are noticing that the flowers are larger than usual this spring, it’s a possibility your ash tree has been infested with ash flower gall midge.

Why do my ash tree’s flowers look weird?
If your ash tree is growing disproportionately large clusters of flowers, it’s likely due to ash flower gall midge. This tiny insect overwinters as females hidden in bud scales and other protected areas of your ash tree. Once spring arrives, the mites lay their eggs on the buds of the male flowers. Chemicals produced during the egg laying process cause the plant cells in the buds to grow abnormally. This causes large, disfigured flowers which then provides an ample food source for the developing mites until summer arrives. By late summer, the mites have moved back to the buds, restarting the process over again.

Will flower galls harm my tree?
Flower galls are more unsightly than they are harmful. After the mites leave, the galls will remain throughout the year, but they ultimately do little to harm the tree. If, however, the trees are infested year after year, it is possible that it can weigh down the branches and potentially cause damage from storms, but it is very rare that this will happen.

What can I do about ash flower gall midge?
Treatment for the mites can be applied in the spring before or just as the buds fully open. This usually happens starting mid-March to May depending on the species of ash. Once galls appear, however, it is too late to treat the tree. The mites are too small to be seen without microscopes, so the only way to know if you have ash flower gall midge is after the galls appear. If you are concerned about ash flower gall midge, or anything else with your trees, please feel free to reach out to our team of ISA certified arborists for a free estimate to get your trees back on track.