GardenLine | Common Saskatchewan Pests | Eriophyid Mites

Flower galls on ash and poplar trees, leaf galls on elm, maple, linden, basswood, birch, poplar and cherries are all caused by microscopic mites. Each species of tree has it is own species of mite. The trees and the mites have evolved together. The mites are highly specialized and usually not reason for majors concern. The galls can be very unsightly, but typically do not do any serious damage. Eriophyid mite galls on flowers and buds can remain on a tree for several years before falling off. Mite galls that form on leaves can discolour or distort foliage, and even though the leaves drop in the fall, the mite infestation may return.

Description

Eriophyid mites are very small, and are only visible using a microscope. The mites are worm like, and have only two pairs of legs. Males and females appear identical. They are poor crawlers and the primary method of population spread is by wind.

It is much easier to identify a gall mite infestation by the distortion of leaves and flowers, rather than by trying to find the mites. The galls that are formed on flower buds of ash and poplar are woody and gnarled in appearance. The galls on leaves are green, yellow, red or purple in colour. The leave galls are bladder, blister spindle like fleshy projections. The galls are found mainly on the topside of leaves. There is a yellowing directly underneath the galls with a pore in the centre of the discolouration.

Life Cycle

Eriophyid mites over winter as specialized winter hardy females which crawl into bark crevices or buds (depending on the mite species). Females emerge in the spring and travel to the flowers or leaves. The males deposit packet of sperm on the leaves, the females find the packets and fertilize themselves. The female then lays eggs, which hatch and go through two larval stages. The adults live for approximately one month. There are several generations per year. When the leaves start to harden, late in the year, the specialized winter hardy females are produced. These females fertilize themselves and move to winter shelter.

Damage

Mites produce galls by injecting a chemical into plant tissues during feeding. These chemicals cause the plant tissues to grow abnormally. Typically the galls are most plentiful early in the year on new growth and foliage, and primarily found in close proximity to the trunk. The bud galls will stop further twig and leaf development.

Control

As the mite gall cause no serious damage, no treatment is necessary except for aesthetic reasons. Pruning out infested twigs and destroying infested twigs in the late spring is a good means of control as it removes the adults. If the infestation is severe, a dormant oil mixture or a miticide such as Kelthane may be sprayed early in the spring.

Several hybrid poplar appear to be immune to flower gall mite. Selection of these hybrids should be considered in order to avoid gall mite infestations. The 'Northwest' poplar is particularly susceptible to gall mite.

Sources

Ives, W.G.H. & H.R. Wong. Trees and Shrub Insects of the Prairie Provinces. Edmonton: Canadian Forestry Service: Inf. Rep. NOR-X-292. 1988. Johnson, W.T. & H.H. Lyon. Insects that Feed on Trees and Shrubs. Ithica: Cornell U.P. 1988.

Philip, H. & E. Mengersen. Insect Pests of the Prairies Edmonton: University of Alberta; Extension. 1989.

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Sustainable horticultural information, offered free of charge to the public with the support of the University of Saskatchewan Extension Division, the Department of Plant Sciences and the Provincial Government.