Hello Paul,

Thank you for contacting Extension Master Gardner helpline with your question. 

We suspect this may be related to the fertilizer since 4-5 times in a row may burn the roots and then you would see dieback. 

If you scrape the bark with their fingernail is it still green underneath?

Thank you,

Hello Paul,

Yes it is a good sign. Don't give up hope yet! Don’t fertilize anymore and water once/week if it is dry.

I've included a couple of additional extension lilac care resources below:

Cornell Cooperative Extension Lilac Care: https://chemung.cce.cornell.edu/resources/lilacs

Iowa State University Growing Lilacs in the Home Garden: https://yardandgarden.extension.iastate.edu/how-to/growing-lilacs-home-garden

Good Luck!

Paul,

I also wanted to add that you may wish to consider a soil test. This will give you a good idea of levels in your soil for your landscape and what and how much soil amendments may be needed, if any, before adding fertilizer any place else on your property.

If you decide to do this, you can find more information here: https://www.uvm.edu/extension/agricultural-and-environmental-testing-lab.

Thank you!