Are the white flies on a plant or in a greenhouse? If your greenhouse is infested you will need to spray with and insecticide made for whitefly. Your local garden center will be able to recommend the formula for your weather conditions. If you have a hanging basket such as verbena (they always seem to get whitefly) try spraying the foliage with a strong jet of water to disturb them. Then repeat in 10 minutes. Then repeat a third time. This has been shown to upset them so much that you drastically cut down on the population. Also remember that allowing a plant to dry out will attract whitefly. Keep growing, Marianne Binetti