Several Honey Locust trees here in Southern Ontario have been the target of small green bugs that have been distorting honey locust leaves and, in some cases, partially defoliating these trees. The main culprit has been the honey locust plant bug (Diaphnocoris Chlorionis). The honey locust plant bug (Diaphnocoris chlorionis) are approximately 3mm (1/8 inch) long when full grown and light green in colour. They pierce leaf tissue and suck the juices out causing leaf distortion, chlorosis and partial defoliation of the tree. Honey locust trees can handle light feedings, even a couple of years of heavy feedings, but beyond that the life of the tree may be at risk.
The Honey Lotus Plant Bugs begin feeding on leaf buds causing damage to these emerging leaves. Once the buds have opened they begin feeding on the underside of leaves. They pierce the leaf tissue and suck the sap from the leaves. This piercing and feeding causes leaf distortion and chlorosis. A light feeding will cause a yellow stippling of the leaves while a heavy feeding will kill the plant cells and cause premature leaf drop. Trees that are heavily infested will notice significant defoliation.
The insects overwinter in the bark of twigs as eggs that hatch as nymphs in the spring just as the buds are beginning to swell. Most of the damage occurs before the leaves are fully developed. By late May or June the adults appear and continue to feed for one to two months then disappear mid to late July after laying their their eggs in linear clusters under the bark of 2- and 3-year-old twigs. There is one generation per year. (Morton Arboretum (n.d.)).
In most cases no control measures are required. A mature honey locust tree will usually be able to recover on its own (even a partially defoliated tree will begin putting on new foliage by mid-summer). To help reduce further stress to affected trees make sure they are well watered and fertilized.
Blasting the tree with a strong jet of water may kill some of the population, as will dormant oil or insecticidal soap, but it is difficult for home gardeners to spray high enough on a mature tree. Pruning July or later may also help to remove some of the eggs that have been laid in the twigs. If your Honey Locust Plant Bug populations are very high, you may want to secure the services of a professional arborist to spray the tree with an insecticide.
Photo Credits: all photos have been taken by the author.
MortonArboretum (n.d.); ‘Honey Locust Plant Bug’; Retrieved on Jan. 15, 2021. from: https://www.mortonarb.org/trees-plants/tree-and-plant-advice/help-pests/honey-locust-plant-bug
Hahn J., (rev. 2019). Honeylocust plant bugs. University of Minnesota. https://extension.umn.edu/yard-and-garden-insects/honeylocust-plant-bugs
ISU Extension and Outreach, (n.d.). Honeylocust plant bug and leafhopper. https://hortnews.extension.iastate.edu/honeylocust-plant-bug-and-leafhopper
Michigan State University, (2015). Honeylocust plant bug and Honeylocust leafhopper. MSU Extension Integrated Pest Management. https://www.canr.msu.edu/resources/honeylocust_plant_bug_and_honeylocust_leafhopper
Oregon State University, (n.d.). Honey locust (Gleditsia triacanthos)-Honey locust plant bug. A Pacific Northwest Extension Publication. https://pnwhandbooks.org/insect/hort/nursery/hosts-nursery/honey-locust-gleditsia-triacanthos-honey-locust-plant-bug
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