Ask-a-Dave's-Gardener: Rockroses dying, 2 by TJH0

TJH0 wrote:
My rockroses are dying. I have lost 2 of 6 over the last 12 months and another is on its way out. The leaves get sticky and then they brown and fall off and then the stalks turn brown and dry up. It takes a few months to lose a five foot plant. I have tried spraying with NEEM oil - but it doesn\'t seem to help. The plants have been in the ground for about 3 years on a hill in clay soil. Here are some photos.
Thanks for any help!
Teresa