Whiteflies are tiny pests that can become big problems for your garden. Not only does their feeding damage your plants, they can also transmit plant viruses. This can add up to headaches for growing tomatoes and other plants. The most common species of this garden pest are the bandedwinged, greenhouse, silverleaf and sweet potato whiteflies. Unfortunately, all these species have somewhat broad host ranges.

Adult whitefly

Say hello to an adult whitefly.

Photo Credit: ©2004 Buglady Consulting

Whitefly eggs

These are whitefly eggs.

Photo Credit: ©2004 Buglady Consulting

Whitefly hatchling

This hatching green lacewing larva will be an excellent predator of the immature stages of whiteflies.

Photo Credit: ©2004 Buglady Consulting

What do whiteflies look like?

Adult whiteflies resemble tiny moths and are covered with a white waxy powder. They’re rarely more than 1-3 millimeters long and are typically found on the undersides of leaves. Immature forms have a scalelike appearance and are sometimes mistaken as scale insects.

Bandedwinged whitefly (Trialeurodes abutilonea) adults have brownish bands across their wings, and their body is gray. Greenhouse whitefly (Trialeurodes vaporariorum) adults hold their wings flat over their bodies. The pupa has sides that are parallel to each other with hairs covering it. Silverleaf whitefly (Bemisia argentifolii) is a bit smaller and more yellow. Its wings are held rooflike at about a 45-degree angle. The pupa case is more domed-shaped, with a few random hairs. Sweet potato whitefly (Bemisia tabaci) is similar to silverleaf whitefly, with adults holding their wings in a rooflike manner and dome-shaped pupa with few random hairs.

What kind of damage do whiteflies cause?

Adult female whiteflies insert their eggs into the leaf tissue of a plant. A minute larva in the “crawler” stage hatches out and begins to feed on this leaf tissue by inserting its mouthparts into leaves and sucking sap from the plant tissue. At this stage, the pest is called a scale (not to be confused with a scale insect, which at this stage it resembles greatly). While feeding, a sticky waste substance is excreted by the insect (commonly called honeydew). This liquid adheres to leaves and provides a medium for sooty mold to colonize and grow. Sooty mold is black and eventually covers leaves and stems. This mold inhibits infected portions of the plant from photosynthesizing and also causes aesthetic damage.

After growing through several life stages, the larvae finally enter a pupal stage. Here, becoming sexually mature, whiteflies take on the adult form and eventually emerge as winged adults.

Infested plants are seemingly chlorotic (turning yellow), causing some plant varieties to have a silvery appearance. Whiteflies also produce honeydew. This sweet, sugary liquid adheres to leaves and promotes a black mold (known commonly as sooty mold) that colonizes and grows on the leaf surface. Sooty mold eventually covers leaves and stems. It inhibits infected portions of the plant from photosynthesizing, as well as causes aesthetic damage. Ants are often present as well – they feed on the sugary honeydew waste droplets.

How to you control whiteflies?

Some simple observation can go a long way. Spraying for this pest with insecticidal soaps or horticultural oils when the whiteflies are in their immature (scale) stage will give you a much better kill then other life stages. (Trying to spay the flying adults is next to impossible.)

Remember that horticultural soaps and oils don’t have systemic properties, which means when spraying the product, it must come in contact with the pest. So for whiteflies, the immatures are on the underside of the leaves – this is where you must target.

A word of warning: You can burn leaves with horticultural soaps and oils. These products need to be applied when the air temperature is cool out. Make sure your plants were watered well the day before you apply treatment – never spray wilted plants. Read the labels and make sure your application site is listed. Following labeled rates also reduces the risk of leaf damage. Follow the label directions! More is not better! And make sure beneficial insects are not present when you spray – insecticides can kill the good guys, too.

In addition to sprays, there are many whitefly predators and parasites out there. Many natural enemies move in once the whiteflies do. Beneficial insects, like tiny wasps, lacewings, ladybird beetles and minute pirate bugs, among others, can help you out in the garden. If these beneficials don’t visit naturally, you can purchase some of them from commercial insectaries through the Internet. Plants like dill and yarrow (and others) can be planted to attract the good guys in as well.

Sometimes removing the plant is the best solution. If you choose to do this, don’t leave the pulled plant lying around – whiteflies will still be able to hatch and infest your other plants.

Whiteflies can be a pest in your garden. Make sure you treat them early to prevent them from spreading. With a little observation and smarts you can get them under control.