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University of Minnesota Extension

Ash plant bugs

Quick facts

  • The ash plant bug (Tropidosteptes amoenus) feeds on green, white and black ash trees. 
  • Ash plant bug damage typically only affects a mature tree's appearance and not its health. 
  • The best management is to tolerate and ignore the damage. 
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 ash plant bugs

  • Ash plant bugs are oval.

  • Nymphs range up to 1/8-inch long. Adults grow up to 1/4-inch long.

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

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

  • Both nymphs and adults produce small, 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 that emerge 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

  • Ash plant bugs use needle-like mouthparts to pierce leaf tissues and feed on the sap. 
  • In 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.
  • Ash plant damage affects only the appearance of ash trees, especially vigorously growing mature trees. It rarely affects their health. 
Severely damaged leaves may look twisted and deformed
Damaged leaves may appear scorched

How to protect your trees

Feeding by ash plant bugs only affects the appearance of ash trees, not their health. The best solution in most cases is to ignore and tolerate them. 

If it is necessary to use an insecticide, apply it to the leaves where the nymphs are first active during the spring. Later applications of pesticides are less effective. 

  • Low risk pesticides
    • Pyrethrins need to directly contact insects to be effective. Avoid spraying bees and beneficial insects as these products are toxic to these non-pests as well. 
    • Insecticidal soap is a low risk pesticide that can be effective against the nymphs. Spray has to come in direct contact with the nymphs to be effective. 
    • Repeat applications of pyrethrins and insecticidal soap might be needed. 
  • Broad spectrum, residual insecticides, such as pyrethroids (permethrin and bifenthrin), acephate and carbaryl, are also effective against ash plant bugs. 

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 2019

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