Whiteflies are tiny, heart-shaped flies that rest in very large numbers on the undersides of leaves. When the plant is disturbed or brushed up against, the flies will fly out in a great, sudden cloud. These annoying insects aren't only a nasty surprise for plant owners—who find themselves engulfed in swarms of flies—their nymphs and various larval stages attach to the plant's soft tissues and feed on the plant.
Like other sucking insects, they also secrete honeydew, which raises the risk of fungal diseases and attracting still other pests.
Whiteflies are nothing if not prolific. They hatch from tiny, cone-shaped eggs into small scale-like insects that can travel along the plant's stems. The scales molt into nymphs, which then go through several more growth stages before going into a brief resting stage then emerging as adult flies. During almost every step of their development, they continue to feed on the plant. The whole lifecycle takes about 30 days, but this varies depending on the temperature. In warmer weather, they reproduce more quickly, and in colder weather, their growth cycle is slowed.
Whiteflies are a common problem in greenhouses, warm climates, and indoors. They cannot tolerate cold weather, but an indoor whitefly infestation can quickly spiral out of control. It's best to treat whiteflies at the first sign of infection.
How to Get Rid of Whiteflies
Like most pests, the best control for whiteflies is defensive. Healthy, vigorous plants are less susceptible to infestation than weak, underpotted, and stressed plants. As a general rule, make sure your plants are healthy, and you're less likely to attract these annoying critters in the first place.
If you see whiteflies on your indoor plants, there are several control options:
- Vacuum them away. Being careful not to damage the plant, you can use your vacuum cleaner's hose attachment to hoover up adult whiteflies. Make sure that any newly hatched whiteflies can't escape from your vacuum bag!
- Sticky tape. The same sticky tape that works for houseflies can be used for whiteflies. Hang it from the infected plant if possible and follow label directions.
- Insecticidal soap. Insecticidal soaps are available on the market (such as Safer's Insecticidal Soap), or you can make your own by using a dish detergent such as Ivory Liquid. Try to find a product free of perfumes and additives that might harm plants. Mix the soap in a weak concentration with water (starting a 1 teaspoon per gallon and increasing as necessary). Spray on plants. These will help control the population but are unlikely to wipe them out.
- Neem oil. Neem oil is derived from the neem tree. Use according to label instructions. In addition to its insecticidal properties, neem is also a fungicide and has systemic benefits (meaning the plant absorbs it so it can control insects it doesn't directly contact). According to the Environmental Protection Association, neem is safe for use on vegetables and food plants as well as ornamentals. Like insecticidal soap, neem is useful for controlling whitefly populations but might not eliminate the problem.
- Kitchen insect spray. This all-purpose insect spray was developed by the editors of Organic Gardening magazine and came to me by way of Rodale's Organic Gardener's Handbook of Natural Insect and Disease Control. To make a batch, combine 1 garlic bulb, 1 small onion, and 1 teaspoon of cayenne pepper in a food processor or blender and process into a paste. Mix into 1 quart of water and steep for 1 hour. Strain through a cheesecloth and add 1 tablespoon of liquid dish soap. Mix well. The mixture can be stored for up to 1 week in the refrigerator.