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.
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.
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.
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.
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.
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