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University of Minnesota Extension

Ash plant bugs

Quick facts

Ash plant bug (Tropidosteptes amoenus) belongs to a group of insects that pierce leaf tissue with their needle-like mouthparts and feed on the sap.

  • The ash plant bug feeds on green, white and black ash trees.
  • Ash plant bug damage only affects the tree's appearance especially when the tree is mature.
  • Plant health is not affected by ash plant bug infestations.
  • If the damage is severe it can impact the health of young, recently planted trees.
  • The best management technique is to tolerate and ignore the damage.
  • Contact a landscape care service for treatment of larger trees.
Black adults and reddish nymphs of ash plant bug seen on a leaf with discolored patches
Adults (left) and nymphs (right) of ash plant bug
Black spot-like droppings on the underside of an ash leaf
Droppings of ash plant bugs on the underside of an ash leaf

How to identify an ash plant bug

  • Ash plant bugs are oval and range up to 1/8" long as nymphs and ¼" long as adults.

  • Nymphs are pale yellow/red to brown/black and look like large, mobile aphids.

  • Adults are more slender than nymphs and have wings that cover the abdomen.

  • Both nymphs and adults produce black sticky droppings on the underside of infested leaves.

Life cycle

Ash plant bugs produce two generations each year. Eggs hatch in the spring just after the ash leaves begin to expand.

First generation adults appear in June. They then mate and deposit their eggs on the midribs of leaves. Nymphs hatch from the eggs and mature into second generation adults by July or August.

The second generation adults mate and lay their eggs on twigs, bud scales and other protected places in the bark. These eggs live through the winter and hatch in spring. Second generation adults remain active until the first hard frost.

While the second generation of ash plant bugs is active for a longer time, the first generation causes more damage to leaves. The young leaves coming up in the spring are more sensitive to the saliva of plant bugs.

Yellow spots make the green ash leaves look blotchy
Ash plant bugs make ash leaves look blotchy.

Damage caused by ash plant bugs

  • In early spring, nymphs feed on new shoots, leaf stems and the underside of leaves.
  • This feeding can create tiny yellow spots on the leaves that can merge into each other and make the leaves appear blotchy.
  • Leaves may wilt, turn brown and appear scorched. The leaves may also twist and look deformed.
  • Damaged leaves can remain on the tree until the fall season. Damage due to the ash plant bug should not cause leaves to fall in the spring.
  • If leaves are falling in the spring it is usually caused by the plant disease ash anthracnose or stressful environmental conditions.
A green leaf on an ash plant looking brown and burnt
Damaged leaves may appear scorched.
Brown colored, twisted and deformed leaves on an ash plant
Severely damaged leaves may look twisted and deformed.

How to protect your trees from ash plant bugs

Carefully check trees for insects in early spring before or as leaf buds open. Treat only to minimize damage to the leaves.

If insect numbers are high enough to need treatment, pesticides should be sprayed 7-10 days after the leaf buds open in spring and when the nymphs first become active. Later applications of pesticide are not as effective.

  • Use less toxic, effective products first.

    • Pyrethrins have relatively low toxicity and have little impact on many beneficial insects including natural enemies.

  • Insecticidal soap is a low impact pesticide that can be effective against the nymphs.

    • Spray has to come in direct contact with the nymphs to be effective.

    • Repeat applications might be needed.

  • Be sure to spray the undersides of the leaves where plant bugs are normally found.
  • Broad spectrum, more toxic pesticides are also effective options:

    • Permethrin

    • Acephate 

    • Bifenthrin

    • Carbaryl 

  • Large trees are usually best treated by a professional tree care service provider.

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

Jeffrey Hahn, Extension entomologist

Reviewed in 2018

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