If you see tiny whiteflies everywhere in your garden, especially when you brush up against a plant, then it is time to create your plan of attack!  They will attack hundreds of kinds of plants, sucking the juices out of the leaves, spreading viruses and other diseases as they go, and their excretions make plants sticky, moldy and extremely unattractive.  Two methods you can try:

1.  Make a spray , this was developed by the USDA:  Add 1 Tablespoon of insecticidal soap to 1 cup vegetable oil (peanut, safflower, corn, soybean or sunflower).  SHAKE well, then add 1-2 teaspoons of this mix to 1 cup water.  Spray the diluted solution directly onto the insects every 7-10 days until you get the problem under control.  Be sure to spray the undersides of the leaves because the solution has to come in contact with the insects to be effective.  Be careful because this could burn the tender leaves of certain plants (squash, cabbage, etc.0 and be sure to wash vegetables well at harvest to resudues left.
2. Garlic spray.  Puree a couple cloves of garlic with a pint of water in a blender.  STRAIN and spray.
3. Get some beneficial insects- tiny wasps that parasitize whiteflies, or lacewings and ladybugs will eat them.  Let your herbs flower to attract these.
4. Sticky traps- buy them online from a variety of sources, or make them yourself! Cut rectangular pieces (about 3×4″) of plastic or durable ccardboard.  Drill a hole at one side for hanging or putting on stick.  Paint surface of both sides bright lemon yellow, the color that attracts whiteflies.  When it is dry, coat the pieces with an insect-trapping adhesive such as Tanglefoot, which you should find in any garden supply store.  Position them around your garden a few inches above the plants..the more the better.  Here’s more info:
5. Organic Neem Oil can be sprayed on vegetables, fruit trees and flowers to kill eggs, larvae and adults. Mix 1 oz/ gallon of water and spray all leaf surfaces (including the undersides of leaves) until completely wet.
6. Organic horticultural oil will kill them at all stages. Note: Ants feed on the honeydew that sucking insects produce and will protect these pests from their natural enemies. An application of Tanglefoot Pest Barrier to the stalks of roses and other woody plants will help get rid of ants.