I'm in Arizona growing a green bean plant for the last three months. The leaves started dying and then I started seeing white and black spots in the undersides of the leaves. I also saw some spider webs on the plant. So I did some research and sprayed the plants with a mixture of 1 Tbsp vinegar and 2 L water. It started working and I was happy. But then the black spots started showing up again and the green beans that were growing aren't growing anymore. Any suggestions on what's causing it and how to save the plants?