Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Bugwood.org

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Summary

Galls are irregular plant growths that are induced by a range of different of insects and mites. Maple leaves often host a variety of brilliantly colored, odd-shaped galls, which are caused by eriophyid mites and gall midges. While these galls may be aesthetically unappealing to some, they do not affect the overall health of the infested tree and rarely warrant control.

Maple Bladdergall Mite

Classification

Scientific name: Vasates quadripedes, Shimer, 1869
Family: Eriophyidae (Gall mites)
Order: Trombidiformes (Trombidiform mites)

Hosts

Red maple (A. rubrum), silver maple (A. saccharinum), and sugar maple (A. saccharum)

Description

Maple bladdergall mites induce globular growths about 2.5–3 mm in diameter on the upper leaf surface (Figure 1). These galls are usually noticed during May, about the time the leaves are fully expanded. The galls are initially green, then turn red, and eventually black. In some cases, galls become so abundant that infested leaves become deformed (Figure 2).

Maple bladdergall mites overwinter as adults under bark scales and other protected sites on the host tree. Early in the spring they migrate to newly expanding leaves and begin to feed. Galls have an opening on the underside of the leaf, so mites can exit the gall if necessary. Mating and egg deposition also takes place within the gall. Young mites hatch from the eggs and remain within the gall until they reach maturity, at which time they move to new leaves to start new galls.

Figure 1. Maple bladder galls. Photograph by epic2112 via iNaturalist, used under a CC BY-NC 4.0 license.

Maple bladder galls infestation — Figure 2. Heavy infestations of maple bladder galls can deform leaves and reduce a leaf's ability to photosynthesize. Photograph by Michael Cooper via iNaturalist, used under a CC BY-NC 4.0 license.

Maple Spindle Gall Mite

Classification

Scientific name: Vasates aceriscrumena (Riley & Vasey, 1870)
Family: Eriophyidae (Gall mites)
Order: Trombidiformes (Trombidiform mites)

Hosts

Sugar maple (A. saccharum)

Description

Maple spindle gall mites induce small, elongate, projecting galls on the upper surface of foliage (Figures 2, 3). The galls are green but may turn pinkish. In high abundance, they can give the leaf a spiked appearance (Figure 4). Otherwise, the life history is similar to that described for maple bladdergall mites above.

Figure 3. Maple spindle galls. Photograph by Timothy Frey via iNaturalist, used under a CC BY 4.0 license.

close-up of maple spindle galls — Figure 4. Close-up of maple spindle galls. Note the elongate form of the galls. Photograph by Nick Furlan via iNaturalist, used under a CC BY 4.0 license.

spindle galls on maple leaves — Figure 5. Maple leaves heavily infested with spindle galls. Notes the spiky appearance of the leaves. Photograph by karenandphillip via iNaturalist, used under a CC BY-NC 4.0 license.

Erineum or Felt GallMites

Classification

Scientific name: Aceria spp., Aculops spp.
Family: Eriophyidae (Gall mites)
Order: Trombidiformes (Trombidiform mites)

Hosts

Red maple (A. rubrum), silver maple (A. saccharinum), sugar maple (A. saccharum), Norway maple (Acer platanoides), mountain maple (Acer spicatum)

Description

The exact fall morphology varies somewhat between mite species and host trees, but in general the galls are green or red fuzzy patches resembling felt on the lower and upper leaf surfaces (Figure 6). Like other gall mites, heavy infestations can impact the photosynthetic potential of individual leaves but don't generally impact overall tree health (Figures 7,8).

Figure 6. Light erineum gall infestation. Photograph by Jason M Crockwell via iNaturalist, used under a CC BY-NC-ND 4.0 license.

erineum galls patches — Figure 7. In heavy infestations, individual erineum galls can merge into larger patches that sometimes cover an entire leaf. Photograph by Joe Walewski via iNaturalist, used under a CC BY-NC 4.0 license.

heavy erineum gall infestations on maple leaves — Figure 8. Dying maple leaves with heavy erineum gall infestations. Note the dry, crinkled appearance of the infested leaves compared to the healthy leaves in the background. Photograph by Kelly Krechmer via iNaturalist, used under a CC BY-NC 4.0 license.

Box Elder Pouch Gall

Classification

Scientific name: Aceria negundi
Family: Eriophyidae (Gall mites)
Order: Trombidiformes (Trombidiform mites)

Hosts

Box elder (Acer negundo)

Description

Box elder pouch galls look like an expanded pouch on the upper leaf surface (Figure 9) and an open dimple filled with white pubescence on the underside of the leaf (Figure 10). Infestations that occur when leaves are growing can cause leaf deformities (Figure 11).

Figure 11. Box elder leaves deformed by box elder pouch galls. Photograph by Sam Kieschnick via iNaturalist, used under a CC BY 4.0 license.

Eyespot Gall Midge, Occelate Gall Midge

Classification

Scientific name: Acericecis ocellaris (Osten Sacken, 1862)
Family: Cecidomyidae (Gall midges)
Order: Diptera (True flies)

Hosts

Red maple (A. rubrum), silver maple (A. saccharinum), sugar maple (A. saccharum), striped maple (A. pensylvanicum), mountain maple (Acer spicatum), Freeman’s maple (A. x freemanii)

Description

Eyespot galls form in the spring. They begin as small yellow-green circles (Figure 12). As they mature, they grow into a circular red blister surrounded by green surrounded by red that deepens into maroon (Figure 13). Midge large feed for about a week, during which time they can be observed on the underside of the gall (Figure 14). After feeding, they drop off the leaf and pupate in the soil. Adults emerge the following spring.

Figure 12. Young eyespot gall midge galls. Photograph by Deborah Barber via iNaturalist, used under a CC BY-NC 4.0 license.

Figure 13. Galls produced by eyespot gall or occelate gall midges. The red-yellow-red circles are distinctive. Photograph by David Coyle via iNaturalist, used under a CC BY-NC 4.0 license.

Figure 14. Eyespot gall midge larvae on the underside of a leaf. Photograph by Deborah Barber via iNaturalist, used under a CC BY-NC 4.0 license.

Leaf Vein Galls

Classification

Scientific name: Dasineura spp.
Family: Cecidomyidae (Gall midges)
Order: Diptera (True flies)

Hosts

Red maple (A. rubrum), silver maple (A. saccharinum), sugar maple (A. saccharum), striped maple (A. pensylvanicum)

Description

Specific gall morphology varies by midge species, plant host, and time of colonization. When galls form on full-grown leaves they appear as swellings along veins on the underside of the leaf (Figures 15–17). Discoloration or slight malformation may be evident on the upper leaf surface (Figure 18). When galls form during leaf growth, they can cause the leaves to become misshapen.

Figure 15. Young leaf vein galls appear as small swellings along the leaf vein. Photograph by rowanny via iNaturalist, used under a CC BY-NC 4.0 license.

Figure 16. Older leaf vein galls appear as larger swellings along a leaf vein. Photograph by Bill MacIndewar via iNaturalist, used under a CC BY-NC 4.0 license.

Figure 17. Leaf vein galls can be red, which gives them a stark contrast to an otherwise green leaf. Photograph by joannedaniel via iNaturalist, used under a CC BY-NC 4.0 license.

Box Elder Bead Gall

Classification

Scientific name: Contarinia (undescribed species)
Family: Cecidomyidae (Gall midges)
Order: Diptera (True flies)

Hosts

Box elder (Acer negundo)

Description

Box elder bead galls are small green to pink, spherical swellings that form on the upper surface of the leaf along the midrib (Figure 19). A single larvae is found in each gall (compare to box elder bud gall midges below). Adult midges have not yet been reared from the galls and are undescribed.

Box Elder Bud Gall

Classification

Scientific name: Contarinia negundinis Gillette, 1890
Family: Cecidomyidae (Gall midges)
Order: Diptera (True flies)

Hosts

Boxelder (Acer negundo)

Description

Box elder bud galls are irregular, elongate or globose galls that form along the midrib of box elder leaves (Figures 20–22). Galls are formed early in the spring when young leaves are still expanded, so galled leaves are often severely deformed. Box elder bud gall midges are gregarious, so multiple larvae may be found inside each gall. Larvae develop quickly. When mature, they emerge from the gall and drop into the soil, where they spin a cocoon. Larvae pupate in the fall and emerge the following spring as adults.

Damage

In general, leaf galls are not harmful to the health of a tree. The brilliant red color of eriophyid galls sometimes alarms some people who believe the trees are "diseased" or seriously damaged. Occasionally, photosynthesis (food making process by plants) may be reduced in individual leaves that are heavily infested. If many leaves on a tree are heavily infested, there may be some reduction in growth.

Management

Deciduous trees like maples lose their leaves every fall and can withstand large amounts of leaf damage without suffering ill effects. So leaf galls do not seriously affect the health of a tree and chemical control is seldom warranted. If necessary for aesthetic reasons, it is best to treat an infested tree for eriophyid mites using a registered pesticide in mid-April before buds swell as adult mites move from their overwintering sites to new growth at this time of the year. This treatment may help reduce the eriophyid mite population on an infested tree.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

Authored by Greg Hoover, 2004; revised by Michael Skvarla, 2023.