My 'Sunburst' honey locust is not growing well. What could be the problem?

FAQ
Question: 

My 'Sunburst' honey locust is not growing well. What could be the problem?

Answer: 

The ‘Sunburst’ honeylocust has distinctive yellow-green foliage.  Unfortunately, it is not a vigorous tree.  It grows slowly and is susceptible to cankers and mimosa webworms.

Cankers, caused by fungal pathogens, are localized dead areas on branches, twigs, and the trunks of trees.  The most common canker on honeylocust is Thyronectria canker.  It typically attacks trees weakened by adverse environmental conditions or poor care.  Thyronectria cankers are usually elongated and slightly sunken with callus ridges at the canker margins.  Initially, the surface of the destroyed bark is orange-brown.  It later bleaches to bright yellow-orange.  Fungal cankers cannot be controlled with fungicides.  The best way to prevent cankers from attacking trees is to keep the trees in good health with proper care. 

Mimosa webworms are grayish brown caterpillars.  Damage occurs when the caterpillars tie the honeylocust leaflets together and feed on the foliage inside the protective webs.  Damaged areas eventually turn brown.  There are two generations per year.  If necessary, mimosa webworms can be controlled with insecticides.  Insecticides must be applied shortly after egg hatch (typically mid-June and early August in Iowa) and before webbing is apparent.

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