discovered this white foamy substance on my lilac - not sure how old the tree is but it was likely planted around the time the house was built - about 60 years ago
the yellow jackets & flies are attracted to it so it's possible that it is sap
any help with identifying the cause and possible cure appreciated
Spittle bugs, maybe? Put some bug killer on it and see if it goes away. If you do not use poison, wipe it off with a soft tissue and see if it comes back. Luciee (;^)
I don't think it's spittle bugs--it seems a bit late in the season for them, plus their spittle is usually smaller and on leaves/green stems/tender growth, not on the trunk of a tree. It's also not sap. I suspect a slime mold of some sort (something along the lines of the dog vomit fungus, etc). I would try removing it (hose it off? put on gloves and manually remove it?) and see if there's a rotten area or something underneath it.
Is the plant showing any signs of distress? I think most likely it doesn't indicate a serious problem with the lilac, but it would help to know if there were any other symptoms that the plant might be less than healthy.
We had a good bit of rain and the white substance was washed off for a couple of days but I noticed today that it is back. No sign of distress so far other than the bark is peeling off in the area around the white stuff. I'm sure it's not spittle bug - that tends to be more like a lot of tiny little bubbles - this is thicker and creamier. This is making me think that it is some kind of pest that has gotten under the bark. It's not easily accessible so it's a bit hard to see. The yellow jackets are still loving it too.
