Walnut Gall Mites

Description

• Eriophyid mites are about 1/100 of an inch long and are not visible to the naked eye. Related to spiders and scorpions, the pests have two pairs of legs and sausage-like, long bodies. The insects are highly mobile on infested trees. The mites are carried to other trees through wind and birds. The pests have sucking mouthparts that they use to feed on tender tree areas like stems, buds and foliage.

Damage

• Walnut gall mites are basically parasitic pests that infest trees for sustenance. Their feeding causing deformity in the cells of the affected areas. The signs of infestation are raised blisters on foliage uppersides where the insects feed. The areas under the blisters are covered with white fuzz that contains the gall mites. The damage incurred from gall mite feeding is primarily aesthetic in nature. Gall mite infestation has no effect on tree health or the production of nuts.

Growth Cycle

• The pests overwinter within the crevices in the walnut tree bark, or on fallen leaves and buds in the form of adult females. During fall and winter, the females go into dormancy or hibernation. The females also go dormant during very hot weather. The pests get active during early spring at the time of new foliage growth and immediately start to lay eggs and feed. A single female lays up to 80 eggs in a month. These hatch into female and male mites within two weeks. The pests do not mate and the female is fertilized with the sacs that the male scatters on foliage surfaces.

Control

• No control is necessary for walnut gall mites as the insects do not damage trees. Prune out the affected leaves and dispose. In cases of high population, spraying the buds and twigs with products containing carbaryl or oxythoquinox is effective. Use pesticides on warm days during early spring at the time of bud swell for best effect. Spraying trees with dormant oil spray is not recommended for walnut trees.