I love our gardenias, almost as much as the white flies. Every year we struggle for control of the bushes that remind us of paradise and remind the white flies of...well I don't know. Anyway, I've been assured it is a loosing battle. I've been told by one Extension Agent that I should Shovel Prune my gardenias and be done with it, but we love them too much to do that. So the struggle goes on year after year. Since we limit our use of insecticides to emergency infestations of house eating monsters, I'd like to share our more natural techniques to wrestling the white flies to a draw.
My white flies are attracted to a particular shade of yellow, specifically the yellow the color of the plastic in Preston Antifreeze jugs. Accept no substitutes; we've tested several other kinds of yellow product. The attraction is so strong that I've found white flies hanging around a jug of Preston I left next to the garage last week. Auto shop dumpsters are a good source for empty Preston jugs.
We wash out the jug and cut a number of 2X2-inch squares and then rig hangers from string or wire. Then we smear the yellow plastic squares with Vasoline or some other viscous oil from the kitchen to make them sticky. Hang the square in each infested bush near the infestation. Check weekly. Clean off the stuck flies and recharge with petroleum jelly if needed.
This and a light spraying with insecticidal soap solution keep white flies in check around here.