What's eating my gleditsia triacanthos 'sunburst'?

Gleditsia 'Sunburst' is most troubled by the mimosa webworm, whose caterpillars web and skeletonize leaflets in mid-to-late summer. Honey locust plant bug causes stippled, distorted foliage in spring. Thyronectria canker can weaken branches. On balance, the mimosa webworm is the pest most likely to cause dramatic visible damage.

Webbed masses of brown, skeletonized leaflets; unsightly in late summer; severe infestations can cause early leaf drop Prune out and destroy web masses as soon as they appear; spray with Bt or spinosad when larvae are small; avoid planting near honey locusts with established infestations

Stippled, yellowed, and distorted leaflets in spring from feeding on plant sap Insecticidal soap or pyrethrin spray targeting nymphs in late April to May; damage is usually cosmetic and trees recover

Leaflets fold and gall around tiny orange larvae; distorted, stunted new growth Remove and destroy infested shoot tips; systemic insecticide in spring at bud break for persistent problems

Sunken, discolored bark with dieback of branches; orange-red fruiting bodies on bark Prune out affected branches to healthy wood; sterilize tools; avoid wounding bark; keep tree vigorous with adequate water