I have a Mexican lime tree, 6 years old. Has been a good producer up until 2 years ago. Under the leaves there is a white sticky substance and on top of the leaf is a dark covering or mold looking substance. Some limbs are dying off the main trunk, seems to dry up and leaves start to fall. The fruit has been very small and sparce. Is there a spray that can be applied to kill this disease? Also, I thought I saw a white looking fly on the tree.
Lime Tree Leaf Disease
Certified GKH Gardening Expert
The sticky substance is honeydew and the result of pests, possibly aphids. In addition, the mold you see is likely sooty mold, which is also a result of the insect pests. Getting rid of the insects will take care of the problem. Neem oil is good for this. It will take care of both the insects problem as well as the sooty mold. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm