Hello,

I am sorry about your tree! This canker is generally exacerbated by drought stress. Last year was one of the driest in our history and many trees are suffering. Fungi can attack trees that are stressed.  Winter watering is very important when we experience long periods of drought. To treat you absolutely should remove the dead branches with sterilized tools and clean up under the tree as well. Sadly our research says there is no spray will eradicate the fungi, instead we need to look at what is stressing the tree and try to manage that, whether it be mites, compaction of soil around the tree, injury to the tree or cankers. Promoting good tree health is the best defense!

I am attaching several research based facts sheets about Honey locusts, cankers and management that could aid you in making your decisions regarding this tree in the future.

Good Luck!

https://extension.colostate.edu/topic-areas/yard-garden/honeylocust-diseases-2-939/

http://hyg.ipm.illinois.edu/pastpest/200107d.html

https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/