TechNotes Sept. 10 - Whitefly Management

TechNotes are provided by Sygenta GreenCast.

The greenhouse whitefly (Trialeurodes vaporariorum) and silverleaf whitefly (Bemisia argentifolii and the Q- and B-biotypes of B. tabaci) and are the most prevalent whitefly species to infest ornamental crops. Over the last couple of years, the Q-biotype whitefly has become more prevalent and is often more difficult for growers to control since it is less susceptible to many of the insecticides that growers rely on to control the other whitefly species.

Whitefly adults appear, like their common name suggests, as small white flies measuring 1/16 to 1/12 inch long. It is difficult to distinguish between the various species and biotypes of whiteflies. The greenhouse whitefly is larger than the silverleaf whitefly and holds its wings fairly flat over its abdomen in such a way they appear almost parallel to the leaf surface. The silverleaf whitefly holds its wings roof-like over its abdomen, at approximately a 45 degree angle with the leaf surface and has a slight yellow coloration. All life stages are most commonly observed on the undersides of plant leaves.

Female whiteflies can begin laying eggs as early as 1 to 4 days after emerging as adults.  They lay 30 to 150 eggs on the undersides of the younger, upper leaves, often in a crescent-shaped pattern. The spindle-shaped eggs are white at first and turn gray with time. Depending on temperature, the eggs of greenhouse whiteflies hatch in about 8 to 10 days; it takes slightly longer (10 to 12 days) for silverleaf whitefly eggs to hatch. Their lifecycle progresses through four nymphal stages, a pupal stage, and finally the adult stage, where they may live for one or two months. The complete life cycle (from egg to adult) takes an average of 32 days for greenhouse whiteflies and 39 days for silverleaf whiteflies.

Whiteflies have piercing, sucking mouth parts and in many instances do not cause detectable injury symptoms to crops. Severe infestations could cause some plants to turn chlorotic and mottled from feeding, but this type of symptom is fairly uncommon.

Growers should monitor the crop on a weekly basis to determine the presence of whiteflies, and to evaluate the effectiveness of their management strategies.  When monitoring, it is useful to use a combination of methods including sticky cards, random plant inspections, and indicator plants.

One of the best methods to reduce the incidence of whiteflies in the production area is to start with a clean greenhouse, free of any plant materials including weeds and ‘pet’ plants, which may harbor whiteflies. If all the living plant materials can be removed from the production area for at least 7 to 10 days between crops, any surviving adults will soon die from starvation. 

Where possible, growers should prevent the entry of whiteflies into the production area. Inspect all incoming plant materials, such as cuttings, plugs, or stock, for whitefly immatures and adults before being introducing them into the production facility. 

Control Strategies

Growers often achieve effective control of whiteflies using biological control strategies including the use of the entomopathogenic fungus Beauveria bassiana or releasing parasitic wasps Encarsia formosa for controlling greenhouse whitefly and Eretmocerus californicus and Eretmocerus sp. for controlling the silverleaf whitefly. 

There are numerous insecticides available for controlling whiteflies. Systemic insecticides such as acetamiprid, clothianidin, dinotefuran, imidacloprid, and thiamethoxam are very effective at controlling whitefly populations, provided they are applied properly.  These insecticides are most effective when applied to actively growing plants.  All of these systemic products are in the same chemical class and have a similar mode of action.  It is often necessary to rotate the chemical families of the insecticides being applied to prevent their resistance to these chemistries.  Products containing abamectin, acetamiprid, bifenthrin, buprofezin, clothianidin, cyfluthrin, flonicamid, pymetrozine, pyriproxyfen, and pyridaben are all effective and make good rotational partners.

Soil Temperature Map