What Can I Use to Spray for Whiteflies?

Identification

• Although they look like flies or moths, whiteflies are in a different insect group – the Aleyrodidae family. Their feeding habits are similar to those of mealybugs, aphids and scale insects. They suck sap by piercing plant tissue with a modified mouthpiece called a stylet. Secondary plant damage occurs when whitefly excrement, called honeydew, creates a food source for sooty mold fungi. As fungi grow, they create a black film on leaf surfaces that prevents photosynthesis. Whiteflies are also vectors, or transmitters, of viral diseases that can compromise plant health.

Water

• Syringing is the method of spraying a stream of water on plants to dislodge pests. The syringing method matched or exceeded rates of controlling whiteflies compared to the use of chemical pesticide sprays, according to the University of California website. Plants must be sprayed at least once weekly at first, with treatments reduced to once every two or three weeks as populations decline. Syringing is recommended because it does not kill natural predators of whiteflies as insecticidal sprays do.

Insecticidal Soaps

• Synthetic chemical pesticides kill natural predators of whiteflies, which is often the best way to control the insects. Whiteflies have a tendency to build resistance to synthetics very quickly, making chemicals an ineffective solution as a long-term control. Insecticidal soap is an organic alternative to synthetic measures that must be sprayed directly on insects, since action is dependent on contact. To prevent plant stress, insecticidal soaps should not be sprayed when temperatures exceed 80 degrees F. Insecticidal soaps may reduce whitefly populations, but will not eliminate them.

Neem Oil

• Neem oil is pressed from the seeds of the Asian neem tree (Azadirachta indica). It prevents insects from molting and laying eggs. Like insecticidal soap, neem oil is a contact insecticide and must be sprayed directly on whiteflies, not just on crawling surfaces. Neem oil does not persist well because it deteriorates when exposed to sunlight and is washed away by rain. Frequent applications are necessary to manage whiteflies; eradicating entire populations is very difficult.