We have two lilacs, one is the “Miss Kim” variety, and the other is “Yankee Doodle” (IIRC). Both have branches where their leaves shrivel, then die. It looks like what you’d expect if they weren’t being watered, but this May and June have been very wet. We have clay soil.
Yankee doodle was planted 1 1/2 years ago, had a lot of flowers last spring, and only a few this spring, which I understand is normal. It’s lost most of its leaves, but still has a few smaller stalks whose leaves look OK. The Miss Kim is 4 or five years old, and has lost a couple of stalks. We cut the first off, and a second then began to go, so we cut that off also. We were going to cut off the dead and dying parts of the Yankee Doodle, but since that’s most of the plant, I thought I’d ask here first.
My WAG is it’s root rot, due to the wet spring and clay soil, and they’re both probably goners no matter what we do, but does anyone have any other ideas what it might be? Also, should I cut off all the dying parts, or leave them on? The wood is still green even though the leaves have died, so I was wondering if there’s any chance the branches would recover next year.
One more thing. Mrs. 'Beam has heard something about lilac borers. We’ve looked and haven’t seen anything obvious, but we don’t really know what the signs of lilac borer are.
Lilacs seem pretty near indestructible where I’m from, but those are mostly the old ones brought from England a hundred years ago or more, not named varieties.
It wouldn’t hurt to check the bases of the stems for signs of chewing, but I’ve never seen it myself.
If it is root rot, the only solution is to amend the soil. Your best bet is to dig them up with as large a root ball as you can conveniently handle, then enlarge the hole and refill it with a mix of sand and topsoil. They grow well in the Prairies, so some lime wouldn’t hurt.
I suspect the problem is related to poor drainage and damp weather. I wouldn’t give up on a plant or individual stems if the wood is still green.
I’ve had a similar problem here with a couple of shrubs. If it comes to replanting, try amending the soil in a fairly wide area, rather than just the planting hole (if you confine amendments to the hole, it can act like a sink and draw water from the badly-drained surrounding area), and plant the root ball a couple of inches higher than the surrounding soil, creating a little mound.
