Question
I have a mimosa tree that has a lot of white bugs on it. I thought they were flies, but they do not move when I poke at them. They appear to be stuck on tree. They are multiplying quickly. They are also in clusters and are all over the tree. What can I use to kill them. I also have a severe ant problem. But I used ant killer to control those.

Answer
Sounds like Cottony scale- an insect.
The cottony scale  is a highly modified insect pest that commonly attacks silver and red maples. The scales are usually first noticed when the females produce an egg sac which appears as a 1/4 to 1/2-inch long ball of cotton. Heavy infestations can result in branches being turned completely white with the egg sacs. Like most scale insects, the nearly mature insects, the adults and the eggs are resistant to pesticides and the anxious tree owner must wait until the correct time for management.

Normally, this scale is a mere curiosity and nuisance. The white egg sacs easily attract attention and the developing scales produce honeydew. Honeydew is the excess water and sugar excreted by many plant sap-feeding insects. Honeydew is commonly mistaken for "plant sap" being dropped on cars, sidewalks and lawn furniture lying under trees. When honeydew collects on leaves and branches, bees, wasps and ants are attracted to the area. If the honeydew is allowed to remain, molds called "sooty fungus" grow on the material, turning the surface a gray-black color.

Occasionally, heavy outbreaks of this scale occur, usually on weakened or stressed trees. These outbreaks can cause the death of numerous small branches and occasionally the death of a tree.

This pest has numerous parasites and predators that normally keep its populations in check. However, every few years, these natural controls seem to fail and the cottony maple scale can reach epidemic proportions. Unfortunately, weak trees can be severely damaged during these outbreak years. Healthy trees often loose a few small branches and have no apparent long term problems. What makes management of this scale more difficult is the fact that insecticide applications may actually cause the scale problem to continue longer than normal. This is caused by poor timing of a pesticide application that kills most of the parasites and predators but allows survival of the resistant scale stages.

Trees in restricted street lawns or suffering other stresses from drought, compacted soils, poor fertilization, etc. are the ones most likely to exhibit major branch or crown dieback. Improving the tree growing conditions will significantly help the trees survive the cottony maple scale attacks until the natural predators and parasites build up to effective levels. The most important predators are several black lady beetles that have two red spots on the upper surface.

Imidacloprid (Bayer Advanced Garden Tree & Shrub Insect Control Concentrate) is applied as a drench around the root zone of infested plants. This water soluble insecticide is taken up by the roots and transported throughout the plant where it is ingested by sap feeding insects. This provides a means of scale control without reliance on sprays.

The ants are gathering the honeydew and will go away when the scales are controlled. You can treat around the tree with a ant bait type insecticide this will be carried back to the ant nest and kill the nest. There are several on the market ask your nursery/ garden type store for an ant bait.