I am new to growing citrus and fruit trees so I need your guy's help. My lime tree is curling at the tops only with new growth leaves and it seems to have something black under the leaves. They don't appear to be moving like insects. I thought they were aphids but I tried spraying them with a canola oil, water and dish liquid soap mixture I seen online but it doesn't seem to be helping. I have three more nearby; lemon, orange and lime trees and none of them seem to have this problem. The white liquid in the photos is the mixture I was telling you about. Any suggestion on how to fix this?