Plant Diseases/Dead locust tree branches
I have a "Shademaster" locust tree that I planted about 20 years ago. It has grown into a big shade tree that is everything the description said when I bought it.
I have noticed that in the last few years some of the ends of the branches are dying and this year 1 whole limb is dead. Also the bark is peeling on some of the branches.
A nursery center employee (not where I bought it) said they are fast growing but a short lived tree. Is this true? Or does it have some disease?
Cultivars of Honeylocust are fast growers as you mentioned- some growing up to 2 feet/year.
A thinning canopy can be an indication of disease or insect activity. The tree would need to be examined by a professional arborist or horticulturist to determine the cause of decline. Honeylocust is prone to several diseases ranging from leafspots to a severe canker disease caused by the fungus Thyronectria. There are a few insect pests such as borers that can tunnel inside the wood. Here in the South or Southeast, the tree does not fair well in hot/humid weather and in heavy soils. It has been said to have been overplanted in some areas. I am not sure of the life expectancy under ideal climate conditions.
To get an examination of your tree, suggest contacting an arborist with your city or contacting the Agricultural Extension Office (usually an office in each county and often housed in the courthouse) to arrange for a "house call" to see your tree and evaluate its overall health status.
If there is internal decay, thinning will continue to progress. Eventually, removal may be the best option, especially if there is a danger of person or property damage.