Bladder, spindle, and erineum (felt patch) galls are created on maple by eriophyid mite species in the genus Vasates. The gall growths on the host plant leaves, while often conspicuous and abundant, are typically of no detriment to the overall health of the host plant. Leaves next to the trunk and larger branches are often most impacted in the early spring. Upon maturity, the eriophyid mites leave their galls and travel to other newly developing leaves and initiate more gall development. Mite activity will eventually decrease as the growing season progresses. For example, the maple spindle gall (V. aceriscrumena; spindle-shaped gall) occurs frequently on sugar maple whereas the maple bladdergall mite (V. quadripedes; rounded gall) is more common on silver and red maples. Both species form galls on the upper leaf surfaces. In high populations, it is possible for leaf distortion to occur. Erineum or felt patch galls are produced on either leaf surface (upper or lower) on maple, typically by eriophyid mites in the genus Aceria. In general, these maple gall mites overwinter as adults beneath bark scales, in sheltered areas. Adults are not visible without magnification, such as a hand lens. Mites are 0.15 mm in length, elongated in shape, with 4 legs located near their head. In the early spring, they move to the opening leaves and begin feeding. The mites causing bladder or spindle galls feed on leaf undersides. Initially, a slight depression is formed in the leaf. Leaves produce pouch-like galls that enclose the feeding mite. Openings remain in the undersides of the leaves opposite the gall. Feeding continues within the gall, where mites lay numerous eggs. Most species are prolific in their reproduction, and mites will eventually leave their galls in search of new leaf area to infest. Typically by July, these species of eriophyid mites end their activity. Populations of these mites tend to fluctuate greatly year-to-year.
Depending upon the species, circular (bladder) or spindle shaped galls are created. Eriophyid mites in another genus also cause felt patch or erineum galls on similar hosts. Galls will change color over time as they develop, from green to red. These galls are nondamaging to the overall health of the tree but some may consider them an aesthetic nuisance. Management is rarely needed. Population size fluctuates greatly year to year. In rare cases, leaves may become deformed or distorted.
Visual scouting of newly developing leaves in the spring is useful for monitoring the newly developing galls. Management is likely unnecessary, unless the amount of leaves impacted by galls becomes aesthetically unacceptable. Multiple years of monitoring are necessary to make this decision - and population fluctuations can happen leading to fewer mites and fewer galls in subsequent seasons naturally. Unless early leaf distortion or dieback occurs every year, management is likely not necessary.
Because the adult eriophyid mites overwinter on the bark, raking up and removing previously infested host plant leaves likely will not reduce their populations. Removing and destroying severely infested branches prior to mite emergence from the galls may help reduce the population on a single tree, however the efficacy of this is not entirely understood. Educating clients or property managers about the insignificance of eriophyid mite galls on the overall health of the host plant may be the primary means of cultural management for these insect relatives.
Naturally occuring predatory mites feed on some eriophyid mite species, and should be preserved by choosing reduced risk pesticides if chemical management options are selected. Parasitoids impacting eriophyid mite populations are not known at this time.
Abamectin (NL)
Carbaryl (L)
Horticultural oil (L)
Pyrethrins (L)
Pyrethrin + piperonyl butoxide (L)
Spiromesifen (L)
Active ingredients that may be applied systemically include: abamectin (injection).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
