Pesticides for Whiteflies

Whiteflies cause problems for gardeners.

Whiteflies are small, whitish-yellow insects that swarm around infected plants when disturbed. Whiteflies kill plants, carry diseases and cause other problems, such as mold. Whiteflies reproduce rapidly and can become a problem if not treated with pesticides, natural sprays or insect predators.

The Whitefly

The two major types, the greenhouse whitefly and the silverleaf whitefly, congregate on the lower and upper leaf surfaces. The flies are approximately 1/8 inch long. Silverleaf flies have a yellow tone. Whiteflies are similar to aphids, scales and mealy bugs. Dark gray to orange-colored, cone-shaped eggs are laid in a crescent pattern on the undersides of leaves. Sometimes mistaken for scale, white, flat, oval-shaped nymphs hatch from these eggs in four to 12 days.

Whitefly Destruction

Whiteflies move from one plant to another. After hatching, the whiteflies attack leaves, buds and stems by piercing the outer layer of plant to extract liquid. Infested plants turn brownish-yellow. Growth becomes stunted, and the plant may eventually die. The honeydew secretion left behind by the flies promotes growth of a sooty mold, which also hinders the plant. Whiteflies can also spread plant viruses. The silverleaf whitefly causes fruit to ripen unevenly. Not all plants are susceptible to whiteflies, but ones that are can die within a matter of weeks.

Pesticides

Pesticides can be effective against whiteflies. Found at gardening and farm supply stores, most sprays contain pyrethrum, a botanical poison that paralyzes on contact. Other options include mycopesticides or mycopathogens, which consist of microscopic fungi that feed on insects. This type of spray is safe for humans. Imidacloprid, a synthetic insecticide, is extremely effective against whiteflies and needs only to be sprayed once a week.

Safe and Natural Alternatives

Always treat plants purchased from a nursery before introducing them into the garden. Since whiteflies gain resistance to chemical pesticides, it is a smart idea to rotate pest control. A simple sticky fly tape attracts and kills the adult whiteflies without using any chemicals. A dilution of liquid dish washing soap and vegetable oil works by smothering the larvae and eggs and kills adults and nymphs. Ladybug larvae consume up to 1,000 whitefly eggs and feed on nymphs as well. A homemade wash made of onion, cayenne, garlic and oil is effective when sprayed weekly.

References

• Evergrowing.com: Plant Bugs and Pests
• Garden Harvest Organic: Dealing with Whiteflies
• University of California Integrated Pest Management Program; How to Manage Pests: Whiteflies; 2008
• University of Minnesota; Whiteflies in Commercial Greenhouse Poinsettia Production; Michael J. McDonough, Daniel Gerace, Mark E. Ascerno; 2008