I have some large, old lilacs that seem to be dying. They start out great in the season, then leaves on individual branches start to get a variegated look, then curl, then brown, then finally die.
I have many lilacs, but three in particular seem to be suffering. They are situated in a row, north to south. I moved into this house in 2012 and the three were doing great. I sprayed a bit of herbicide on the brick pathway near the lilacs at that time, being careful not to hit any lilac shoots. Maybe the timing was uncanny, but about two weeks later, the south lilac began to curl and brown and finally the entire plant was dead in about 6 weeks. I chalked it up to bad luck with the herbicide.
The next year, the two remaining plants did great and had no issue. The south plant even grew back a little, but only about five percent of what it was. Again, I just figured it was bad luck with the herbicide.
This year the same thing is happening with the middle plant and slightly with the north plant. I have sprayed no herbicides and asked my neighbor if she had sprayed any. She had not. It is not bad luck with the herbicide. The south plant came back a bit more than the previous year, but it is also dying in the same fashion again.
So I've done some research to find out what it is.
- I've learned about a bacterial blight, but a description I read of how the leaves look when dying does not fit.
- I've learned that lilacs are susceptible to over watering, but that is not a problem, because I rarely water them and I don't think runoff is a problem for their location.
- I've learned that under watering can be a problem, but I doubt it because my other lilacs in other locations are doing fine with the same watering attention.
- I've learned that over fertilizing can be a problem, but I don't fertilize much and didn't the first year when the south plant died (but the previous owner might have).
I'm in the inland Northwest USA.
I'm not sure what to do and would be very saddened if I lost the other two. Here are my pictures of the plants. Click on them to see a larger view.