MAPLE GALL MITES

Spindle galls on maple

Several species of mites feed on maples and induce the formation of foliar galls. Three of the most common mites are the maple bladdergall mite, Vasates quadripedes (Shimer) on silver and red maple, the maple spindlegall mite, V. aceriscrumena, and a group of Eriophyes spp., which causes felt-like pink or red patches on upper and lower leaf surfaces of various maples. Galls of the maple bladdergall mite are somewhat rounded in shape, and those of the spindlegall mite, as the name suggests, elongate and spindle-like in shape. When galls are numerous, the leaves appear deformed.

Close up of maple spindle galls

Adult mites, less than 2mm long, overwinter under bark scales on the trunk and branches. In spring, when the leaf buds begin to expand, the mites move to the leaves and begin to feed, causing abnormal cell development. The formation of galls is caused by a plant-growth substance or enzyme produced by the mite. Each species of mite produces a different growth substance resulting in various shapes and sizes of galls which are characteristic of each species. The developing gall encloses the feeding mite. Female mites lay numerous eggs within each gall. The emerging larvae continue feeding through two moults and reach the adult stage in a matter of weeks. Mature mites leave the gall and crawl to new leaves. There, they continue feeding on foliage until July, and initiate the development of new galls. The mites then migrate back to the bark to overwinter.

CONTROLS

The severity of mite populations and degree of damage, varies with the season. Generally, losses of leaf surface due to gall formation, have an insignificant effect on large, mature trees, and control measures are unwarranted. However, on smaller or newly planted trees having less foliage, gall formation may be a significant stress. Handpicking of damaged leaves from lower branches will reduce mite populations. Dormant oil sprays, applied before budbreak in early spring, will also reduce overwintering mites. Dormant oil should not be used on Japanese or sugar maple due to problems of phytotoxicity.

W.A. Attwater/M.D. Dykstra

PDCF-061 (Revised 97/08/26)