Maple spindle gall: what extension services say

This page describes what the named extension and forest service publications say. It does not identify a gall on any particular tree, say whether a tree is healthy, or tell anyone to treat or leave it. Pesticide advice in a source is mentioned only in general terms, and the guide on who may apply pesticides covers licensing. Its round look-alike on red and silver maple has its own page, maple bladder gall.

What it looks like

Ohio State University Extension (fact sheet ENT-60, David Shetlar and Jennifer Andon, April 16, 2015) describes thin, elongate bladders rising from the upper leaf surface. The Maine Forest Service sheet on gall mites (April 2000) calls them slender, erect galls about 5 mm high and as thick as the lead of a pencil. Cornell University's fact sheet on galls on plants (July 1972, as posted by the Maine Department of Agriculture, Conservation and Forestry) gives about 1/5 inch long and about as thick as pencil lead, standing erect and easily seen. Nebraska Extension in Lancaster County (May 14, 2024) calls it a thin, almost worm-like structure growing up from the upper leaf surface. Virginia Tech Extension (Galls and Rust made by Mites, publication ENTO-147, revised November 28, 2022) says spindle galls are narrow, tall, upright growths, green when young and turning pink or red with age, each holding many mites living together.

Which maples

Ohio State places the gall on sugar maple, and Nebraska calls it common on sugar maple. Maine says it is more common on sugar maples than on red and silver maples. Cornell says it is found on soft maples and sugar maples. Virginia Tech says spindle galls occur on maple and other plant hosts. The round bladder gall, by contrast, is a red and silver maple gall in the Ohio State, Maine and Virginia Tech texts.

What causes it

All the sources name a mite as the cause. Georgia calls both gall mites eriophyid mites, and Maine says most galls on deciduous trees are caused by eriophyid mites. Ohio State, Maine and Georgia give the species as Vasates aceriscrumena, spelled slightly differently in each. The University of Georgia Extension page, which covers the bladder and spindle gall mites together, says the adults cannot be seen without a hand lens, are white to clear, about 0.15 mm long and cigar-shaped with only four legs at the front, that there are several generations a year, and that the adults overwinter in bark cracks. Ohio State says the overwintering mites live loose under bark and around the callus of wounds, scars and pruned branches. As the maple leaves first appear the mites move to the expanding buds and feed on the underside of the leaf buds, which raises a blister that becomes a hollow bladder or spindle as the leaf grows. The mites enter the cavity and breed inside without mating, and new mites mature by late June to mid-July, when the galls dry out and the adults leave to find winter sites. Maine says the eggs hatch in about a week and that the gall mites go into hibernation by early August.

Whether the sources call it harmful

Ohio State says spindle galls rarely distort the leaf, though large numbers can make leaves unsightly, and that maple leaf galls seldom, if ever, cause permanent injury beyond looks and possible early leaf drop. Nebraska uses the same words. Maine says the galls are not detrimental to the tree's health, and that its main reason for suggesting control is the appearance of the foliage. These describe the galls in general, not any one tree.

Where the sources differ on management

Ohio State says control measures are generally not recommended because the galls are only a matter of looks. Georgia says control is usually not necessary in the landscape, though it notes that a chemical treatment may prevent new galls. Maine, in 2000, described sprays and a dormant oil, with a caution about oil on oil-sensitive trees. Ohio State adds that Norway maples and some named cultivars with strong red or yellow leaf colour appear resistant. This page gives no product names, rates or timings.

Look-alikes the sources name

Ohio State names the maple velvet erineum gall, crimson to yellow velvet-like patches that can be mistaken for a fungus, and the maple gouty vein gall, thickened pouches along the veins of sugar maple made by a midge. The wider group is on the tree galls page.