What is Ash Flower Gall?

Ash flower gall, also known as ash flower mite gall or ash flower gall mite, is a common plant disease that affects ash trees. It is caused by a microscopic mite called Eriophyes fraxinivorus. This mite feeds on the flowers of ash trees, causing abnormal growths or galls to form. These galls can be found on the male and female flowers of the tree, and they can vary in size and shape.

How Does Ash Flower Gall Affect Ash Trees?

Ash flower gall can have a negative impact on the health and appearance of ash trees. The galls can cause the flowers to become distorted and discolored, and they can prevent the flowers from opening properly. This can lead to reduced seed production and affect the overall reproductive success of the tree. In severe cases, the galls can also cause the flowers to drop prematurely, further reducing the tree’s ability to reproduce.

Identification and Symptoms

Identifying ash flower gall can be challenging, as the galls can vary in appearance depending on the stage of development. In the early stages, the galls may appear as small, green or reddish swellings on the flowers. As they mature, the galls can become larger and more woody in texture. They may also turn brown or black in color. The galls can be found on the male and female flowers of the tree, and they may be present on multiple branches or throughout the entire tree.

Life Cycle of Ash Flower Gall Mites

The life cycle of ash flower gall mites begins in the spring when the mites emerge from overwintering sites. They then migrate to the flowers of ash trees and begin feeding. As they feed, the mites release chemicals that cause the plant tissue to grow abnormally, forming the galls. Inside the galls, the mites continue to feed and reproduce. In the fall, the mites leave the galls and seek out overwintering sites, such as cracks in the bark or leaf litter, where they will remain until the following spring.

Management and Control

Managing and controlling ash flower gall can be challenging, as there are currently no effective chemical treatments available. However, there are some cultural practices that can help reduce the impact of the disease. These include pruning and removing infected branches, promoting overall tree health through proper watering and fertilization, and monitoring the tree for signs of infestation. It is also important to avoid planting ash trees in areas where the disease is known to be prevalent.

Preventing the Spread of Ash Flower Gall

Preventing the spread of ash flower gall is crucial to protecting ash trees from the disease. This can be done by practicing good sanitation measures, such as removing and destroying infected plant material. It is also important to avoid moving infested plant material, as the mites can easily hitch a ride and spread to new locations. Additionally, monitoring and controlling other pests that can weaken ash trees, such as the emerald ash borer, can help reduce the tree’s susceptibility to ash flower gall.

Other Ash Tree Diseases

Ash trees are susceptible to a variety of other diseases, in addition to ash flower gall. Some of the most common diseases include ash dieback, ash yellows, and ash rust. Each of these diseases has its own set of symptoms and management strategies. It is important for tree owners and arborists to be familiar with these diseases and to take appropriate measures to prevent and control them.


In conclusion, ash flower gall is a plant disease caused by the ash flower gall mite. It can have a negative impact on the health and reproductive success of ash trees. Identifying the disease and implementing appropriate management strategies is crucial for protecting ash trees from the disease. By practicing good sanitation measures and promoting overall tree health, it is possible to reduce the impact of ash flower gall and preserve the beauty and vitality of ash trees.