My cherokee purple tomatoes have a problem I've never seen before. About 1/3 of the plant has dried out stems and leaves. The location is random - some at the top of the plant, some at the bottom. There are no spots on the leaves, but there are a few pests on the stems (small black bug with wings - smaller then an ant) but I don't think there are enough to cause this much damage. I live in LA, the weather has been in the 80's and I water about every 3 days. The cherry tomato plants on either side are fine. Any ideas? Photo attached.