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Did you have a late frost in the spring? Many parts of the country did this year and is likely what happened to you. These late frosts killed the flowers on the trees and without the flowers, the tree cannot produce berries or fruit.

Grows best in full sunshine with moderate amounts of water during the growing season. If your tree is young, it may take a few more years before it's mature enough to produce berries. If it's been established for 4-5 years and is still not blooming, it may need more sunshine or additional water during the growing season.

Without seeing it, or the symptoms in question, it would be very hard to say. There are many insects and fungus that will cause the death of trees, and also many environmental issues that could have caused the death as well.

In the meantime, this article will help you to narrow down what is killing off your trees: https://www.gardeningknowhow.com/ornamental/trees/tgen/sudden-tree-death-causes.htm

This is one for your local extension service. They will be able to assist you with this daunting task.

Here is a link that will help you to find the closest extension service to you:

http://www.mgoi.ca

If the area is very windy, or prone high traffic, then you may want to stake your tree. If the area doesn't get disturbed and is protected from wind, then staking the tree won't be necessary, and can cause much more harm than it does good. They need the stress to develop a strong stature!

Here is an article for more information:

https://www.gardeningknowhow.com/ornamental/trees/tgen/should-you-stake-trees.htm

'Joseph Rock' is susceptible to several diseases, including fire blight, as well as pests. For fire blight, prune out the infected branches. These articles should help:

https://extension.psu.edu/mountain-ash-diseases

https://www.rhs.org.uk/plants/95813/sorbus-joseph-rock/details

https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/mountainash.html