Controlling Whiteflies in North San Diego County

Whiteflies are actually little moths that produce a white, waxy substance called “scale” that streams from the plants that are heavily infested. The scale discourages predators and helps the little moths to protect their eggs. If you have a heavy infestation you will also see black mold, which comes from the honeydew that the plant secretes when it is under attack by whiteflies. In our household gardens and shrubbery here in North County, ants are the only insects that are more prolific than whiteflies in transmitting diseases from one plant to another. Thousands of hibiscus plants are killed every summer here by whiteflies and we also see them on citrus, Bird of Paradise, and many other fruit bearing and ornamental plants.

There are several varieties of whitefly in this area and I have seen as many as three kinds on a single Hibiscus plant in Encinitas. They start to develop to infestation levels in the early spring and can reproduce to the point of killing plants in less than six weeks if they are left untreated.

The spiral whiteflies lay their eggs in a characteristic circular pattern that is very noticeable. If you see a spiral pattern of white eggs on the underside of citrus leaves or on that Bird of Paradise plant, it is time to take defensive action.

Whiteflies Control

The best time to control whiteflies is when they first arrive in the spring. You should spend some time looking to your shrubs and trees, inspecting the bottoms of leaves for those telltale spiral patterns. To control whiteflies you will need to treat twice the first week and once a week thereafter until they are fully under control. Because control is so time intensive, it is normally taken care of by a gardener rather than a pest control operator. Treatments consist of:

1. Mix a very small amount of a surfactant (soap or detergent that is safe for plants) into a hose sprayer and use it to clean the flies, scale, and eggs off of the plant. Repeat this spray treatment weekly until the whiteflies are gone. The soap breaks the surface tension of the water which helps to clean the scale, eggs, nymphs, and black mold off the plants.
2. Ask your garden shop for a systemic treatment that can be used in the soil around ornamental plants to control whitefly in the future. Do not use systemic pesticides around vegetables or fruit trees!