Whiteflies are common on a variety of crops grown in open fields and greenhouses. Both adults and nymphs suck the plant sap and and excrete honeydew onto leaves, stems and fruits. Chlorotic spots and sooty molds develop on the affected tissues. During heavy infections, these spots may come together and spread over the whole leaf, apart from the area around the veins. The leaves may later become deformed, curl or take a cupping shape. Some whiteflies transmit viruses such as tomato yellow leaf curl virus or cassava brown streak virus.
Whiteflies measure about 0.8-1 mm and have the body and both pairs of wings covered with a white to yellowish powdery, waxy secretion. They are often found on the underside of the leaves, and, if disturbed, will emerge forming a cloud. They thrive in warm, dry conditions. The eggs are laid on the underside of the leaves. The nymphs are yellow to white, flat, oval and pale green in color. Adult whiteflies cannot live without feeding on a host plant for more than a few days. This makes weed-management an important population control measure.
Biological solutions will vary depending on the specific species of whitefly involved and the crop. Natural insecticides based on sugar-apple oil (Annona squamosa), pyrethrins, insecticidal soaps, Neem seed kernel extract (NSKE 5%), Neem oil (5ml/L water) are recommended. Pathogenic fungi include Beauveria bassiana, Isaria fumosorosea, Verticillium lecanii, and Paecilomyces fumosoroseus.
Always consider an integrated approach with preventive measures together with biological treatments if available. Whiteflies quickly develop resistance to all pesticides, so a rotation of different products is recommendable. Apply products based on or combinations of bifenthrin, buprofezin, fenoxycarb, deltamethrin, azadirachtin, lambda-cyhalothrin, cypermethrin, pyrethroids, pymetrozine or spiromesifen to control the insect. Be aware that preventive measures are often enough to reduce the population to harmless levels.