According to the University of Missouri, whiteflies are 1⁄10 to 1⁄16 inch long, resemble moths and have a white powder on their backs. Whiteflies are dangerous for plants because they pierce into them and suck out the sap, and the plant begins to wither and turn yellow. With a large infestation, the plants may die. Whiteflies can even infect herb plants, and it doesn't matter if they're growing indoors or outdoors.
Remove herb plants that are infested with whiteflies. You will most likely spot them hiding underneath the herb leaves. Remove them before you begin treatment or the whiteflies will infect other plants in the same area.
Introduce lady beetles to the herb plants if the infestation is small. Lady beetles are natural predators that will eat the whiteflies and get rid of them for you.
Cover a few yellow pieces of cardboard with petroleum jelly. Hang them just above the herbs that are infected with the whiteflies. The whiteflies will be attracted to the yellow color and get stuck to the petroleum jelly. Replace the yellow cardboard until you are no longer catching whiteflies.
Vacuum up all of the whiteflies. Be careful as you lift up the leaves of the herbs and vacuum only with a small hand vacuum. Dump the whiteflies in a freezer bag and set them in the freezer for 24 hours before you throw them out. This will kill them.