Hello

Depending upon how much natural water fell last year, these deaths may have been caused by too little of water. Especially if it was dry, and additional water was not added, this could be a potential problem. It will be beneficial to take a soil sample as well. This will tell you what the current pH level is of the soil and whether or not, you actually needed to apply the Hollytone.
Finally, determine whether or not anything else has changed in the front yard location that may have led to the death of such a mature tree, i.e. soil disruption, construction, etc.

Yes, you can contact your local Macomb County MSU Extension office at<personal data hidden> to see if they have any soil kits available for you to pick up or you can order them online at https://homesoiltest.msu.edu/

Thanks for your question.