The other day while out for a walk I noticed some honey locust tree leaves that weren’t looking too good. Honey locust are fairly disease and insect free tree but the last few years we’ve seen the honey locust plant bug (HLPB) do some cosmetic damage to the leaves. The HLPB overwinters as eggs in under the bark of the tree and they hatch around the same time the tree starts to leaf out. The new foliage is damaged by the feeding from the nymphs.
Adults are active until mid-July and we only have one generation per year here in the Omaha Metro area. However, the damage remains on the leaves giving us a false sense that the tree is under constant attack. The leaves are still producing energy for the tree but yearly repeat infestation can gradually affect the overall health of the tree.
When it comes to trying to reduce the damage done is where things can get complicated. Typically infestations vary from year to year and we never know if they will be a problem. The last three years however, we have seen persistent outbreaks. Timing is critical when trying to manage the insect because they hatch right as the new leaves emerge. Applying low impact products such as summer oils or insecticidal soaps will help reduce damage. But when it comes to large mature trees it becomes impractical to spray. Keep trees healthy by installing a wood chip mulch ring around the trunk extending 18”-24”. Mulch should be 2”-4” deep keeping in mind no much should be mounded around the trunk. Supplemental irrigation of 1” of water a week when we are in times of drought. Avoid fertilizing the tree if you fertilize the lawn (too much fertilizer does more damage than good).