By: Anthony C. Arnoldi, Board Certified Master Arborist WI-0102B
Honeylocusts comprise a very important component of the urban forest. They are dependably hardy, tolerate city conditions well and are tough enough to be street trees. The beautiful ferny foliage casts a very desirable filtered shade, useful for allowing grass, perennials and other plants to grow successfully. They are also one of the fastest growing “good” trees with strong wood (as opposed to fast-growing, weak-wooded tree species like willow and poplar). There are many named cultivars offering varying crown shapes and even one with golden new growth. Examples are ‘Shademaster,’ ‘Skyline,’ ‘Moraine’ and ‘Sunburst.’
Despite this impressive list of pluses, they definitely need care to maintain their health. There are two big problems. Nectria canker is a fungal branch and trunk canker disease that can cause branches or even whole sections of the tree to die. Second, honeylocust borer, is an insect that can kill large branches or even an entire tree.
Both of these problems are rarely dealt with because Nectria has no cure and the borers can kill a section of the tree as a first warning before it is spotted. Both are prevented by a specific care regime. There are two main parts:
Control honeylocust leafhoppers! These tiny, light green insects appear in spring and early summer and feed on the foliage. Even moderate numbers in a tree can be such a nuisance that people stop using their patios. Distortion and shriveling of leaves is caused by sucking out plant sap from the leaflets. High numbers defoliate the tree or prevent leafing out. Yearly damage contributes to dieback of branch ends and the acceleration of deadwood accumulation in the crown. Although their damage is not fatal, they do contribute a major stress to the tree. Stressed trees are the ones predisposed to the big problems of Nectria and borers mentioned before. Therefore, controlling leafhoppers will allow more energy for defense against these greater problems. A fall application of the soil systemic insecticide Imidacloprid can keep them under control for all of the next season. The fall application is preferred because Imidacloprid can take time to be fully distributed throughout larger trees. If a fall application is not done, Imidacloprid can be applied in early spring. For calls received after the leafhoppers have already begun feeding, an application of MSR, a soil systemic insecticide, is made. This is also very effective but does not have Imidacloprid’s full-season control and can cause some grass burning. Both systemics work well and take the place of repeated foliar sprays that have the drawbacks of potential drift and the killing of beneficial insects.
Prune on a regular 5- to 6-year cycle to remove crossing and rubbing branches and deadwood. Removing deadwood will increase tree health and allow more resources for defense against Nectria and borers. Pruning eliminates the self-wounding that commonly occurs. The honeylocust’s rapid growth produces lots of crossing points and Nectria canker often infects the bark at these places. Pruning out branches where Nectria has already begun is often possible, especially if caught early. Knowledgeable arborists can recognize this disease and carefully excise much of it from the tree or prevent it from getting started.
As with all trees, it is important to provide basic care to keep honeylocusts healthy. During dry periods, they need to be kept watered and in poor soils, they need fertilization to enable them to defend against Nectria. When mowing, be careful not to damage the surface roots commonly produced.
Honeylocusts are worth the effort! When there are no damaging levels of leafhoppers and they are pruned for health, they look beautiful. Perhaps it is the most dramatic “before and after” trees for pruning. Compliments will come with the luxuriant, neat, clean foliage and the lack of craggy deadwood that commonly congests them. Most importantly, the big problems stay away. That is what a Certified Arborist can do. Then we can appreciate this great class of trees at their full potential of health and beauty.
© Copyright 2007 – Wachtel Tree Science & Service, Inc.