Question
I have a VERY large mimosa tree that is approximately 40 years old. In the last 3-4 years during the summer it has produced a sticky white residue that falls off in what appears to be small flakes. The residue attracts tons of bees and flies to it so I assume it must be sweet. Do you have any idea what this is and what can be done to resolve the issue? Thanks!

Answer
Sounds like an insect called an aphid. These small insect suck the plant juices from the plant and secrete a substance called Honeydew which is high in sugar content and sticky. Bees and ants will harvest this honeydew as food. the white maybe also from the aphids some are called cottony aphids and secrete a waxy material that is white to hid them from predators.   I would treat the tree with an insecticide called Bayer Advanced Tree and Shrub Insect Control. This is a applied to the soil around the tree and the roots will transport it to the leaves and twigs and when the insects suck the plant juices they are killed. Here is a web link to this product. Check with your local nursery for this product. http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html