University of Maryland Extension

Leaf Beetles - Trees

leaf beetles
The imported willow leaf beetle

Leaf beetles feed on the foliage of plants as adults, larvae or both. Feeding by the adults appears as holes eaten through the leaf or skeletonization of the lower side of the leaf. Larvae may feed on the surface of the leaf or mine the leaves depending on the species. This is a large group of beetles and there is great variation in size and color. The adults are small to medium sized, and some are metallic. Larvae are usually soft-bodied and vary greatly in shape depending on their feeding habits.

Some common examples of leaf beetles are the locust leaf miner, elm leaf beetle, cottonwood leaf beetle, and imported willow leaf beetle (see above photo).

locust leafminer and damage
Locust leafminer adult and damage on black locust

  • The locust leafminer feeds primarily on black locust. The larvae feed inside and cause blotch mines. In heavy infestations the mines may coalesce and turn the leaves brown. The adults skeletonize the leaf surfaces between small veins. Black locust is tolerant to this pest and control is not recommended. Use good cultural practices that promote tree vigor.

elm leaf beetle and damage
Elm leaf beetle adults, larvae and damage

  • The elm leaf beetle feeds on all species of native and introduced elm and zelkova. Larvae etch the leaf surfaces between the fine veins on the undersides of the leaves. Adults feed between the larger leaf veins and produce shot holes. Heavy feeding causes leaves to turn brown, wither and drop prematurely. Severe infestations can cause trees to develop an unsightly, scorched appearance. Damaged trees may put out a second flush of leaves that are also attacked. Repeated defoliations may reduce tree vigor and increase susceptibility to more serious pests such as the smaller European elm bark beetle. It is responsible for spreading the Dutch elm disease fungus.

Control of this beetle will be most effective when community members cooperate in the use and timing of control measures. This will help reduce the movement of beetles from untreated trees back to treated ones. Sprays should be timed to kill small larvae following egg hatch (mid-late May and July-August in Maryland). M-Trak® is a biological insecticide (Bacillus thuringiensis var. Tenebrionis) that is effective against the elm leaf beetle larvae. It is the safest material available to control this beetle. Labeled conventional insecticides may be used to control both adults and larvae. Read the label care for rates, timing of sprays, and for safety precautions.

Adult beetles may be excluded from the home by screening, caulking and weather stripping. Beetles that gain entry may be swept or vacuumed and disposed of.

cottonwood leaf beetle and damage
Cottonwood leaf beetle adults and larva.

  • The cottonwood leaf beetle feeds primarily on cottonwood, but will attack other species of poplar and willows. Larvae skeletonize leaves between the leaf veins. Adult feeding causes irregular shot holes. In heavy infestations tender terminals may be defoliated. If needed, M-Trak7 (see above) may be sprayed on young larvae.
  • The imported willow leaf beetle (photo at top of page) feeds on several varieties of willow and cottonwood. The larvae feed in groups and skeletonize the lower surface of older leaves. Adults chew holes in young leaves. If needed, the control is the same as for cottonwood leaf beetle. In wet summers, willows continue to grow and usually mask the damage, making sprays unnecessary.

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