What attacks maple: pests and diseases the sources name

This page reports what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. Each row names its source, all read on October 9, 2026. Where this site has a full profile, the row links it, and the regulated status tables are on the linked pages and are not repeated here. Maples are covered species by species in tree species in the agency records, including red maple, silver maple, sugar maple, Norway maple and sycamore maple.

Insects

Agent	What the sources record
Asian longhorned beetle, Anoplophora glabripennis. Full profile	Kind: Wood-boring beetle Hosts: The Canadian Food Inspection Agency lists maple as the group most likely to be affected, with birch, poplar and willow occasionally affected and elm rarely. Forest Research lists maples and sycamores among many known hosts, and says sycamore was the most frequent host in the 2012 Kent outbreak: 26% of sycamores in the area were attacked and 98% of the adults found had emerged from sycamore. Where and status: The Canadian agency says it was found in Mississauga and Toronto in August 2013 and declared eradicated in 2020. Forest Research lists it as not present in the United Kingdom and notifiable, with one outbreak found at Paddock Wood, Kent, in 2012 and no evidence of continuing presence in annual surveys since. Season: No season given on the pages read. Forest Research says most larvae and pupae in the Kent outbreak were in stems and branches 4 to 10 cm across.
Cottony maple scale, Pulvinaria innumerabilis. Full profile	Kind: Soft scale insect Hosts: The Morton Arboretum gives silver maple and boxelder as the primary hosts, and lists other maples, white ash, hackberry, dogwood, beech, apple, oak, linden, elm, black locust and honey locust. Ohio State University Extension says it commonly attacks silver and red maples in Ohio and can reach epidemic numbers on silver maple. Where and status: The Morton Arboretum says the insect is native to North America. Neither page gives a regulated status. Both say it is a minor pest in most years, with populations rising sharply every few years. Season: One generation a year. The Morton Arboretum says overwintering immature females mature by late spring and lay eggs in a white frothy mass, and the crawlers hatch in mid-summer. Ohio State says eggs hatch from mid-June to August.
Maple bladder gall (eriophyid mite). Full profile	Kind: Mite gall Hosts: University of Missouri Extension says the bladder-like galls appear on red and silver maples. Where and status: The page covers Missouri trees and gives no regulated status. It says the galls are rarely detrimental to the overall health of large trees, though heavy infestations can disfigure leaves and cause early colour change and leaf drop. Season: Galls about 1/8 inch across appear in spring, light green at first, then red, then black by the end of summer. Adult mites overwinter under bark and in buds, move to the unfolding leaves in early spring, and leave the foliage in fall.

Diseases

Agent	What the sources record
Tar spot of maple, Rhytisma species. Full profile	Kind: Leaf fungus Hosts: Natural Resources Canada lists red, silver and sugar maple as main hosts of Rhytisma americanum. The University of Connecticut says giant tar spot, caused by Rhytisma acerinum, is common in the northeastern United States on Norway and other European maples. Where and status: Natural Resources Canada gives the distribution as eastern Canada and says severe infections are extremely rare and the disease rarely poses a serious threat to health. Neither page gives a regulated status. Season: Connecticut says infection takes place in spring on new leaves, a yellow or pale green spot appears first, and black spots develop in mid to late summer. The fungus overwinters in tarry spots on fallen leaves.
Verticillium wilt, Verticillium dahliae. Full profile	Kind: Soil-borne fungus of the water-conducting tissue Hosts: The Morton Arboretum names maple among commonly infected woody plants, with smoke-tree, catalpa and magnolia. It says streaking in the wood is green in maples and magnolias and brown in most woody plants. Where and status: The page gives no place or regulated status. It says the fungus lives in the soil as resting structures that can lie dormant for years. Season: Acute symptoms are seen in mid-season, often on scattered branches, and chronic symptoms early in the growing season. Only laboratory examination can positively diagnose it.

Agent

What the sources record

Tar spot of maple, Rhytisma species. Full profile

Kind: Leaf fungus
Hosts: Natural Resources Canada lists red, silver and sugar maple as main hosts of Rhytisma americanum. The University of Connecticut says giant tar spot, caused by Rhytisma acerinum, is common in the northeastern United States on Norway and other European maples.
Where and status: Natural Resources Canada gives the distribution as eastern Canada and says severe infections are extremely rare and the disease rarely poses a serious threat to health. Neither page gives a regulated status.
Season: Connecticut says infection takes place in spring on new leaves, a yellow or pale green spot appears first, and black spots develop in mid to late summer. The fungus overwinters in tarry spots on fallen leaves.

Verticillium wilt, Verticillium dahliae. Full profile

Kind: Soil-borne fungus of the water-conducting tissue
Hosts: The Morton Arboretum names maple among commonly infected woody plants, with smoke-tree, catalpa and magnolia. It says streaking in the wood is green in maples and magnolias and brown in most woody plants.
Where and status: The page gives no place or regulated status. It says the fungus lives in the soil as resting structures that can lie dormant for years.
Season: Acute symptoms are seen in mid-season, often on scattered branches, and chronic symptoms early in the growing season. Only laboratory examination can positively diagnose it.

How the sources describe the effects

The range is wide. Forest Research calls the Asian longhorned beetle highly destructive: larvae bore galleries from the cambium to the heartwood and a severe infestation can kill the tree. At the other end, Ohio State says the cottony maple scale is normally a curiosity and a nuisance, with branch dieback only under very high numbers and tree death only rarely in stressed or weakened trees. Natural Resources Canada and Missouri Extension describe tar spot and bladder gall as cosmetic on most trees. Verticillium wilt sits between them: the Morton Arboretum calls it a serious disease that can lead to the death of the host, and says that wilting can come on suddenly in one or more branches.

Look-alikes are named in the sources. Ohio State says the cottony maple scale is occasionally confused with the cottony maple leaf scale, whose females form egg sacs on leaves instead of branches. The Morton Arboretum says streaking helps identify Verticillium wilt but does not guarantee it, because other factors can discolour the wood.

Profiles on this site

The full profiles named in the table are Asian longhorned beetle, cottony maple scale, maple bladder gall, tar spot of maple and Verticillium wilt. The Forest Research and Woodland Trust record for Norway maple in Britain is on the Norway maple page.

Who the sources say to report to