Ash Flower Gall Mite

Problem type: Insect

Name of problem: 
Ash Flower Gall Mite

Plant name(s): Ash

Symptoms / Characteristics:
Ash flower gall mites attack male flowers during blossom development in the spring. The mites feed in the flower clusters making them become irregularly branched and fringed. The galls formed are initially green and turn black as they dry. These galls are large, abnormal masses that can be unsightly and persist on the infected trees throughout the winter and often for up to two years. Galls become more obvious as the tree begins to lose its leaves.

The mites are minute insects that can develop from egg to adult in under two weeks. Many generations can occur throughout the growing season. Mites can move short distances on a tree but are also spread by wind or debris. Mites must have developing green growth to feed on and to multiply, making most of the damage occur in the spring.

Control / Preventions:
Ash flower gall does not affect tree health and vigor and is only considered a cosmetic disease. Control is not necessary unless seed is desired. Brown galls may be removed with a forceful stream of water. Dormant oils can be applied in late winter or early spring before new growth starts. The mites come in contact with the oil causing them to suffocate. Badly damaged flower buds can be pruned out anytime of the year.

Chemical insecticides such as Malathion or Sevin can also be effective for control, but timing of the spray is critical. The window of application is small. Chemicals should be applied 7-10 days prior to bud break.

One last preventative method to avoid ash flower gall mites is to plant only female trees. Both female and male flowers are rarely found on the same tree. These mites attack only male flowers so planting a female tree will avoid infestations.