This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
A chronic problem in greenhouses, whiteflies can also become serious pests during the sultry days of late summer. These sucking insects often appear suddenly, and quickly weaken plants with their constant feeding. Whiteflies are most serious in warm climates where they can survive winter. Good organic whitefly controls include reflective mulches, sticky traps, and vacuuming them from plants.
What Are Whiteflies?
Small, soft-bodied sucking insects, whiteflies look like tiny white triangles, less than one-tenth inch long, when resting on the undersides of plants. Feeding is concentrated on leaf undersides, where whiteflies remove so much plant sap that the plants are seriously weakened. Many species of whitefly feed on ornamental plants, but only one or two are likely to cause problems in the vegetable garden. Whiteflies are most likely to cause problems on okra, tomatoes, eggplant, peppers, and sweet potatoes grown in warm climates. In some areas, whiteflies also damage cucumber and cabbage-family crops.
What Whitefly Damage Looks Like
Pale, wilting leaves are a sign that whiteflies are sucking juices from leaf undersides. As you approach infested plants to inspect the lower sides of wilted leaves, hundreds of tiny white moths take to the air in a cloud. If the whiteflies have been feeding for several days, the leaves may have a sticky substance (whitefly honeydew) and ants may be present as honeydew consumers.
Whitefly Life Cycle
Whiteflies are greenhouse pests in all climates, but they are serious vegetable garden pests mostly in mild winter climates that permit their winter survival. When adult females find suitable host plants, they feed on leaf undersides and lay eggs there. A female may lay 200 to 400 eggs without moving from a plant. Upon hatching, the nearly invisibly small crawlers find a place to feed and insert their sucking mouthparts. Feeding continues for up to three weeks, when nymphs pupate into adults. Frequently problems are not noticed until a 30-day generation has passed, and a population has successfully flourished in the garden.
Diversified organic gardens that include plenty of flowers are poor whitefly habitats because they include such an abundance of natural predators, including lacewing larvae, lady beetles, and predatory bugs. In greenhouses, imported Encarsia spp. parasites are often used to control whiteflies, but they tend to disperse too widely when used outdoors.
Organic Whitefly Control
- Aluminum reflective mulch repels whiteflies by making it difficult for them to find host plants. This is a good way to protect tomatoes and peppers from diseases spread by whiteflies.
- Use yellow sticky traps to monitor or collect whiteflies lurking among tomatoes, peppers, sweet potatoes or cabbage family crops. A half-and-half mixture of petroleum jelly and dishwashing detergent, spread over small boards painted bright yellow, is sticky enough to catch little whiteflies.
- Blast whiteflies from leaf undersides with a strong jet of water. Then apply a weak solution of insecticidal soap, preferably late in the afternoon. Repeat after one week.
- A small vacuum is the best way to remove whiteflies from plants because it will remove both nymphs and larvae. If you have chickens, allow them to peck through infested plant foliage before you compost it.
- Never use chemical insecticides in attempt to control whiteflies. Many strains are pesticide-resistant, but their predators are not. You may accidentally kill many beneficial insects, and the whiteflies will bounce right back.
More Advice on Organic Whitefly Control
Gardens that host an abundance of beneficial insects make poor homes for whiteflies. In areas where whiteflies are common and your neighbors use a lot of pesticides, monitor populations with sticky traps and use a vacuum to keep small outbreaks under control. In seasons following whitefly problems, avoid planting attractive annuals such as lantana, salvia and hibiscus.
More information on organic whitefly control is available from the University of California, Mississippi State University and the University of Missouri.