Key to Common Insect Pests of Elm (Ulmus)


What is the nature of the problem?

Web tents enclosing leaves at end of branches answer: FALL WEBWORM

Spots on leaves, no holes answer: Continue...

Chewing damage on leaves answer: Continue...

Irregularly-shaped tubular growths on leaves answer: ELM COCKSCOMB GALL

Round or oval scales on twigs or limbs answer: Continue...

Tunneling damage beneath the bark on limbs or trunk answer: Continue...


Spots on Leaves, No Holes

Mottled leaves, flat, white bugs and /or spiny black nymphs on undersides of leaves. Small black spots on leaves answer: LACE BUGS

Leaves with many tiny pale spots or dots – elongate wedge-shaped insects present answer: LEAFHOPPERS

Groups of small soft-bodied insects on lower leaf surface, leaves may be sticky with honeydew or covered with sooty mold answer: APHIDS


Chewing Damage on Leaves

Feeding damage on leaf lower surface only; dark larvae present answer: ELM LEAF BEETLE

Greatest leaf damage from top of tree downwards; leaf tissue removed from between veins; iridescent copper beetles may be present answer: JAPANESE BEETLE

Yellow-green larvae curled around twigs while feeding; all parts of the leaf consumed starting at the margin answer: ELM SAWFLY

Shothole feeding damage by tiny brown adults; blotch mines caused by larvae answer: EUROPEAN ELM FLEA BEETLE


Round or Oval Scales on Twigs or Limbs

White and dark brown/black soft scale; edges of scale are dark answer: CALICO SCALE

Oval-shaped reddish brown soft scale surrounded by a white waxy fringe answer: EUROPEAN ELM SCALE

Gray-brown scales, shaped like oyster shells, on twigs answer: OYSTERSHELL SCALE

Dirty white, pear-shaped scale answer: SCURFY SCALE


Tunneling Damage Beneath Bark on Limbs or Trunk

Small brown beetles with heavily pitted wing covers, frass in small branch crotches of healthy trees; multiple galleries radiating from a central gallery in the phloem of stressed trees answer: ELM BARK BEETLE

Reddish pink caterpillars, tunnels in sapwood, frass and sap present at entrance hole in the bark answer: CARPENTERWORM

Damage progress from the bottom, up the tree, girdling it. Deformed trunks, sucker growth may also be seen answer: FLATHEADED APPLE TREE BORER



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