My neighbors come to me for identification and info on tree diseases. I've found every single disease their trees have had, but not this one and it's really bugging me. Please help...
Looks like what remains of a petiole gall caused by an Aphid (Pemphigus species).
Here is a link that might be useful: Petiole gall
Thank you so much ians, that's exactly what it is!!! They will be very thankful and I will definitely give you the credit... :)