The ficus whitefly (Singhiella simplex) is a major insect pest that can completely decimate a ficus or fig tree. Sometimes called the fig whitefly, these tiny white insects suck the juices out of the tree's leaves, causing them to wilt, turn yellow and drop off the tree. Over or under watering, a change in the tree's environment and improper use of fertilizer can also cause these same symptoms, so it's important to make sure your tree is indeed infected with ficus whitefly before you take steps to kill the insects.
Spray the tree with a chemical insecticide, or hang double-sided tape to the branches of the tree, which will trap the tiny adult flying bugs. Note that insecticides are only effective for a little over a week, according to Gene Dempsey, a forestry expert for the city of Fort Lauderdale.
Apply a systematic insecticide (sometimes called neonicotinoid compounds) to the roots of the plant. Mix the insecticide with water and drench the soil around the roots of the tree. Do not waste the solution on dead leaves or other materials collecting around the tree, but make sure it penetrates the dirt. The plant will absorb the killing chemicals and pass them along to the larvae when they hatch and begin to feed. This will protect the tree for up to eight months.
Watch the tree carefully for a week, as it may take time for the systematic insecticide to take effect, and re-apply the insecticide if you see any more adult whiteflies that may have escaped the first application.