I have a bed of English ivy around an oak tree in my yard. It's about 3-4 years old and has done very well. I have kept it trimmed to no more than 6' high, careful to control it within it's ring. However, this year it is browning/dying. There is a large ant colony in the bed I have never been able to eradicate...could it be hurting the ivy? I've not had it bother it before. Today I noticed that 3-4' high on the tree the ivy has no leaves at all! The leaves start at about 3' up the tree. The ivy at the base is also looking very sickly.

What the heck kills English Ivy? I planted it because I thought it was very hardy!