What’s eating my maple trees?

With their bright red or yellow leaves glowing during this time of year, maple trees are one of the most impressive trees in fall. In most Southern states, they are native, whether they are red, Norway, (Norway is a non-native, invasive tree) Freeman or silver. In the northern states, sugar maples provide us with rich maple syrup for pancakes and waffles. But their beauty and usefulness don’t make them immune from serving as lunch to many insect pests, so if you find that the leaves on some of your maple trees are disappearing rather than winding up on the ground, below is a list of some of the most common insect pests of maples.

Ambrosia Beetles

Adult granulate ambrosia beetle, Xylosandrus crassisculus. Photo: J. R. Baker and S. B. Bambara, NCSU, Bugwood.org.

Adult granulate ambrosia beetle, Xylosandrus crassisculus. Photo: J. R. Baker and S. B. Bambara, NCSU, Bugwood.org.

Two species of ambrosia beetles attack maple trees: Xylosandrus crassiusculus Motschulky (granulate ambrosia beetle) and Xylosandrus germanus Blandford. Both are non-native pests. Ambrosia beetles burrow into the xylum and inject a fungus (the ambrosia), which feeds the larvae. In most cases, the fungus becomes a toxin to the tree, and the tree gradually dies. Infected trees can be spotted by sawdust or “frass” toothpicks that jut out of the trunk. Only licensed professional pesticide applicators have the tools to control ambrosia beetles, but homeowners can monitor maple trees for symptoms of decline or for the “toothpicks” to protect other trees from being affected.

Flatheaded appletree borer

Flatheaded appletree borer, Chrysobothris femorata, larvae in frass-filled gallery. Photo: Amy Fulcher, University of Tennessee, Knoxville.

Flatheaded appletree borer, Chrysobothris femorata, larvae in frass-filled gallery. Photo: Amy Fulcher, University of Tennessee, Knoxville.

Flatheaded appletree borer, or Chrysobothris femorata, are bullet-shaped, with a metallic purple abdomen and a metallic bronze ventral (front) side. Adults begin appearing on trees in late spring and early summer. Larvae feed on dividing cambium and sapwood and then bore into the heartwood.  Borers prefer trees that are stressed but will attack healthy trees.

Maple shoot borer

Adult maple shoot borers, Proteoteras aesculana are mottled-gray with wings in a wedge shape when resting. Larvae grow in the shoots, causing leaves to wilt. There are usually two generations of adults per season. As the shoots die, the tree attempts to compensate by creating a new growth that can be “forked” from the main direction of the tree. These forks often need to be pruned to retain one main stem, which will need to be staked to grow straight.

Flagging of maple stem caused by maple shoot borer, Proteoteras aesculana. Photo: Amy Fulcher, University of Tennessee, Knoxville

Flagging of maple stem caused by maple shoot borer, Proteoteras aesculana. Photo: Amy Fulcher, University of Tennessee, Knoxville

Leaf-feeding caterpillars

Several species of caterpillars appear between summer and fall and feed on maple leaves:

  • Green-striped mapleworm (Dryocampa rubicunda)
  • Yellownecked caterpillar (Datana ministra)
  • Orange-striped oakworm (Anisota senatoria)
  • Bagworms (Thyridopteryx ephemeraeformis)
Late-instar green-striped mapleworms, Dryocampa rubicund, feeding on maple leaves. Photo: S. D. Frank, NCSU

Late-instar green-striped mapleworms, Dryocampa rubicund, feeding on maple leaves. Photo: S. D. Frank, NCSU

Yellownecked caterpillar, Datana ministra, on the ground in a nursery surrounded by frass pellets diagnostic of caterpillar feeding. Photo: S. D. Frank, NCSU

Yellownecked caterpillar, Datana ministra, on the ground in a nursery surrounded by frass pellets diagnostic of caterpillar feeding. Photo: S. D. Frank, NCSU

These caterpillars will quickly defoliate a tree, but unless they are in massive numbers, rarely result in the death of a tree.

Potato leafhopper

Potato leafhoppers, Empoasca fabae, feed on the young leaves and buds of over 200 plant species, including maples. When feeding, leafhoppers cause “hopperburn on leaves, appearing as necrotic lines or severe cupping or stunting. Massively infested trees can have “witch’s broom,” losing the “top” or apical dominance of the tree and having branch tips with too many stems. Red maples are more susceptible to damage by leafhoppers than the other maple species.

“Hopperburn” on maple leaves caused by potato leafhopper feeding. Photo: Amy Fulcher, University of Tennessee, Knoxville

“Hopperburn” on maple leaves caused by potato leafhopper feeding. Photo: Amy Fulcher, University of Tennessee, Knoxville

Scales

There are two types of scales: armored and soft. In general they are one of the most difficult pests to control in your yard. Armored scales are topped with a waxy cover, called a “test,” that can be separated from the body and do not produce honeydew, while soft scales have no separate test and produce a carbohydrate-rich waste material called honeydew that can grow mold on the tree or on plants beneath.

Dense population of gloomy scales on the bark of a red maple street tree. Photo: S. D. Frank, NCSU

Dense population of gloomy scales on the bark of a red maple street tree. Photo: S. D. Frank, NCSU

Armored scales feed on the plant tissue, causing branch death and crown thinning. The most common species of armored scales are gloomy scale (Melanaspis tenebricosa) and Japanese maple scale (Lopholeucaspis japonica).

Soft scales feed on the phloem and reduce the amount of energy available for food storage and growth. Twigs and branches begin to die on trees with infestation, and honeydew causes aesthetic damage, also landing on whatever is beneath the infested tree. Long-term infestations can kill the tree. Maple trees are particularly susceptible to scale infestations. The most common and damaging soft scale species are cottony maple leaf scale (Pulvinaria acericola), cottony maple scale (Pulvinaria innumerabilis), calico scale (Eulecanium cerasorum), and terrapin scale (Mesolecanium nigrofasciatum).

Gall-forming insect and mite pests

Although unsightly, galls formed by some insect and mite pests do not damage trees. Galls usually appear in late May and early June and contain a single larva. Larvae exit the gall and drop to the ground to pupate.

The following are the most common mite pests:

  • Gall mites (Aceria elongates): cause blistered white patches on maple leaves and appear in early spring.
  • Maple bladder gall mite (Vasates quadripedes): occurs mostly on red and silver maple trees. Galls are solitary, hollow and have a small exit hole on the leaf underside.
  • Maple spindlegall mite (Vasates aceriscrumena): galls appear in mid-May. Mites leave spindles that are pink or crimson that attach to the leaf surface and are mainly a pest of sugar maples.
  • Maple spider mite (Oligonychus aceris): Eggs hatch in spring and mites feed on the underside of leaves, piercing the leaves and producing a brown stippling. The feeding produces a bronze cast in summer and reduces fall color.

Although most of these pests must be managed by a licensed pest control operator, homeowners can do their part by identifying which pest is attacking their trees. For more detailed information and larger photos, read the original article in the Journal of Integrated Pest Management.

Source: Frank, S.D., Klingeman, W.E., White, S.A., and Fulcher, A. (2013) Biology, injury and management of maple tree pests in nurseries and urban landscapes. Journal of Integrated Pest Management, 4(1): 2013, DOI: http://dx.doi.org/10.1603/IPM12007.

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