Problem Identifier / How to Control Whiteflies on Plants

Whiteflies are winged insects from the Aleyrodidae family. Their soft bodies have a close relation to mealybugs and aphids. Despite the name, whiteflies are not actually flies. The appearance resembles a white moth, but whiteflies and sap-sucking aphids are closely related. Aphids are often confused with whiteflies because they cast off their skins, but aphids do not fly away or flutter upwards when disturbed.

Whiteflies are common in many regions. The tiny size combined with the clusters generally found on the underside of the leaf makes them hard to see. Whiteflies are extremely active during daylight, making them easier to find than many of the other nocturnal insects. Whiteflies reproduce all year long in warmer climates and are usually seen during the summer. They are a general nuisance in greenhouses.

Whiteflies cause damage by feeding on warm-weather ornamental and vegetable plants including okra, eggplant, tomatoes, cabbages, sweet potatoes and peppers. They are also a common pest for cannabis crops.

Identifying Whiteflies

Silverleaf Whiteflies
Silverleaf whiteflies.

The Silverleaf is one of the most common species of whiteflies, with more of a yellow coloration and a smaller size. The average length is between one-tenth and one-sixteenth of an inch. The Silverleaf is extremely common in all the southeastern states. All the species attack a wide range of plants. After sucking the juices from the plant, a sticky substance called honeydew is produced.

Whitefly control is essential because this substance can cause the formation of fungal diseases on the leaves. The feeding of whiteflies causes the plants to become exceptionally weak, often unable to complete photosynthesis. The leaves wilt, then become yellow or pale, and the growth of the plant is stunted. If honeydew is present, feeding has been taking place for at least a few days.

There are often ants in the area because they are attracted to the honeydew. Look beneath the leaves for white insects surrounding the veins. If there do not appear to be any whiteflies on plants, feel the surface of the leaves. If whiteflies are feeding, they will immediately fly away in a swarm. This makes it easy to see the infestation.

When there are whitefly eggs, it means a new generation is going to hatch. The larvae emerging from the eggs look like tiny legless white ovals. The larvae remain stationary, and immediately begin sucking the juice from the plant. The greenhouse species of whiteflies is the most prevalent in California. Whiteflies are found on indoor plants, in greenhouses, and in outdoor plantings all over the state.

The whitefly is like many insects because the nymphs are immature, and eggs are laid randomly by the adults. Look for whitefly eggs in arcs or circular patterns under the leaves. This is where the whiteflies will remain for their entire lives. The nymphs are small, with no legs or wings and oval bodies. The adults have wings and look a lot like extremely small moths.

The giant whitefly is also referred to as a Mexican whitefly. This species has become common in California, attacking both ornamental plants and hibiscus. The giant whitefly was first seen in 1992 in San Diego County before spreading to the southern area of the state, Louisiana, Florida, Texas and certain areas in Arizona. The name was derived from the fact this species is larger than any of the others.

Whitefly Wax Deposit On Cannabis
Whiteflies leave a waxy, thread-like deposit on a cannabis leaf.

The best way to identify this species of whitefly is to look for the wax spirals the adult insects deposit by walking on the leaves. Deposits can be found on the surface of both the lower and upper leaves of the plant. Whiteflies on plants usually lay their eggs in the deposits of wax. These deposits of wax are long filaments resembling human hair, and up to two inches in length, are produced by the nymphs.

The affected leaves have a bearded look due to the filaments. The giant whitefly is attracted to giant birds of paradise, hibiscus, mulberry, banana and certain types of avocado and citrus. All these plants should be examined on a regular basis to determine if there is an early giant whitefly infestation. Natural whitefly control can be achieved by using Trifecta Crop Control as a preventative.

Whitefly Life Cycle

The whitefly life cycle requires about one month for the development of the insect from an egg to an adult. The specific length of time depends on the temperature. The progress of the life cycle includes the four different stages of the nymphs, the conclusion of the fourth instar or pupal stage and the adults. The average lifetime of the adults is between one and two months.

Whitefly eggs are laid by the females on the underside of the upper leaves. The eggs initially hatch into first-stage nymphs, often moving a short distance before remaining stationary and feeding. During the second, third and fourth stages, there is no movement. Towards the end of the last instar, red eyes begin to develop as the insect nears adulthood. Once the adult whiteflies have emerged, there is a hole in the plant in the shape of a T.

What Does Whitefly Damage Look Like?

There is a wide range of damage caused by whiteflies including:

  • Shriveled yellow leaves
  • Prematurely falling leaves
  • Plant death
  • Transmission of viruses
  • Sticky substance (honeydew) on the leaves
  • Sooty mold resulting in dirty black leaves
  • Presence of ants

Whitefly control is difficult due to the combination of fast flight and the insects hiding beneath the leaves. Whiteflies on plants cause two different kinds of damage. Direct damage is often substantial because the plants are drained of juices after the whiteflies feed. The leaves become yellow, shrivel up, and fall off prematurely. A large enough infestation can result in the death of the plant.

The second type of damage is called indirect and is inflicted by the adults. Whiteflies use their mouthparts for the transmission of several different viruses on both healthy and diseased plants. If the leaves are covered with a sticky substance, it is honeydew. The leaves can take on a dirty and black appearance because sooty mold fungus will colonize the leaves.

In smaller amounts, sooty mold will not damage the plants. When the mold is abundant, light is unable to reach the surface of the leaves. This results in excessive stress for the plant. If the plant is sturdy, wash off the sooty mold using a forceful water stream. When there is an infestation, there is a good chance there will be a lot of ants in the general area which you can also wash off.

The worst damage caused by whiteflies is transmitting viruses including the tomato yellow leaf curling virus, the tomato yellow mosaic virus and the tomato chlorosis crinivirus. All these viruses can kill the plant.

How To Kill Whiteflies Naturally

All the options below are effective for getting rid of whiteflies:

  • Trifecta Crop Control
  • Flushing plants with water
  • Vacuuming leaves
Whiteflies On Greenhouse Zucchini
Very heavy infestation on leaf of greenhouse grown zucchini with penny for scale PHOTO CREDIT Whitney Cranshaw, Colorado State University, Bugwood.org

The essential oils in Trifecta Crop Control can also be an effective treatment for whiteflies though we always recommend using it as a preventative to avoid infestations in the first place. It is always easier to prevent pests from landing on your plant than it is to kill them once an infestation has occurred.

For whitefly infestations, apply Crop Control at a dilution rate of 2oz per gallon every 72 hours until the infestation is under control, then switch to preventative of 1oz per gallon, once per week.

Both the pests and honeydew can be removed from sturdy plants by washing the leaves with water. The undersides of the leaves should also be rinsed.

During the early morning hours, vacuum the leaves. This is when the insects are cold and move slowly. Removing the adults prevents them from laying additional eggs. Place the vacuum bag into a plastic bag with a strong seal, then remove it from the area. Infested sections of the plant should be pruned and treated in the same manner as the vacuum bag. This material must never be used for compost because the result will be another infestation.

How to Prevent Whiteflies Naturally

The available options are as follows:

  • Trifecta Crop Control
  • Removing infected plants
  • Reflective mulch
  • Sticky traps
  • Beneficial insects
  • Insectary plants

Controlling a major infestation is not easy. The most effective method is preventing the insects from gathering in the garden or greenhouse. The essential oils in Trifecta Crop Control have been proven to be highly effective to repel whiteflies, thus preventing any infestation. Apply as follows or click here to view and/or download our complete application guidelines.

  • .5oz per gallon applied once per week during veg
  • 1oz per gallon applied once per week during flower up to 2 weeks before harvest

Carefully examine any new plant before purchasing or planting. If there is even a hint of pests, do not buy the plant. When the season first begins, hanging yellow sticky traps close to the plants can assist with not just whiteflies but many other undesirable pests.

If a garden infestation is caught quickly, whiteflies can be controlled by getting rid of the infested leaves or using a water spray to hose down the plants. Reflective mulches and yellow sticky traps are both good strategies for keeping these pests away from vegetable gardens. Also, learn about beneficial insects and look for them in the garden. Additional predators can be purchased from a garden center or attracted to the area.

There is an excellent selection of both insectary and flowering plants available capable of repelling whiteflies. Ensuring the plants remain healthy offers these predators both habitat and food. The most common natural enemies of these whiteflies include small birds, lacewings, big-eyed bugs, spiders and ladybugs. Row covers are effective for denying entrance, but will allow enough water, light and air to reach the plants.

Whitefly Management in Greenhouse Using Biocontrols

You can control your population of whiteflies with several natural enemies. It is critical to be certain you have correctly identified the species before biocontrol is ordered.

Encarsia Formosa

Encarsia Formosa
Encarsia Formosa PHOTO CREDIT David Cappaert, Bugwood.org

Encarsia is a parasite for controlling banded winged whiteflies in your greenhouse. This parasitoid is tiny with a length of 0.6 millimeters. This wasp parasitizes whiteflies in the nymph stage, with the host eventually killed. An egg is inserted by the adult female wasp into the whitefly nymph. Once the egg hatches, the host is consumed by the wasp larvae with death occurring during the pupal stage.

The development of the wasp is completed within the whitefly pupa. The adult wasp chews a round hole in the pupal skin to emerge. Parasitized banded winged and greenhouse pupae turn black as opposed to the brown coloration of parasitized pupae from Silverleaf whiteflies. Once you have introduced encarsia, you need to monitor this stage on the leaves for about three weeks.

Encarsia is extremely effective for the control of populations of both banded wing and greenhouse whiteflies but not as much for Silverleaf whiteflies. You should introduce encarsia every week when first discovering the whitefly stages and repeat every week until a minimum of 80 percent of the pupae has been parasitized. Introduce three to six adult parasites for every square yard.

Monitoring the populations of whiteflies continuously is important once you have stopped the introductions. There are two different systems for introducing encarsia, with a separate practice for each. As soon as you receive your biocontrols, you need to introduce them to the greenhouse. Cards need to be hung evenly through infested plants. Loose pupae can be left alone or disbursed using hanging pots. Tips for introducing encarsia include:

  • If the temperature is below 64 degrees Fahrenheit, adult predators will rarely fly
  • Encarsia should be introduced when you initially see whitefly signs
  • The correct temperature is critical for the searching ability of encarsia
  • Honeydew accumulation from established populations decrease parasitization
  • The adult lifespan is considerably decreased with temperatures above 86 degrees Fahrenheit

Eretmocerus Eremicus (for Silverleaf)

Eretmocerus Eremicus
Eretmocerus Eremicus PHOTO CREDIT Paul Langlois, Museum Collections: Hymenoptera, USDA APHIS PPQ, Bugwood.org

One of the most recent products available for Silverleaf whitefly control is eretmocerus eremicus. The effectiveness for the control of Silverleaf whiteflies is increased. Eretmocerus and encarsia both attack nymphs, killing the pests in their pupal stage. The emergence of the adult wasp occurs by chewing a round hole through the pupal skin of the whitefly.

When eretmocerus parasitize Silverleaf whiteflies, the pupae become a brownish yellow as opposed to the yellow of whitefly pupae. If the temperature of your greenhouse is a minimum of 80 degrees Fahrenheit, eretmocerus is a good choice during the spring. You can introduce eretmocerus at curative levels or weekly with each square yard requiring four to six adults.

Start introductions when you first observe the whitefly stages. You need to continue until a minimum of 80 percent of all whitefly pupae has been parasitized. As soon as you stop introductions, it is important to keep monitoring the populations of whiteflies. There are two systems for eretmocerus introductions with different applications.

No matter which system you choose, an immediate introduction is necessary upon arrival. Cards need to be placed in your greenhouse away from direct sunlight beneath your plant canopy. Tips for introducing eretmocerus include:

  • Do not introduce eretmocerus if whitefly nymphs are not present
  • The minimum temperature for introduction is 70 degrees Fahrenheit
  • Approximately six wasps are required every few weeks for each square meter
  • Examine the leaves while pruning for parasitism development
  • Your employees should receive training for the recognition of parasitized pupae
  • Leaves containing parasitized pupae should be left in your greenhouse to enable the emergence of a new parasitoid generation

Delicatus Catalina

Delicatus catalina is a ladybird beetle between 1.3 and 1.4 millimeters in length consuming whiteflies. Although every whitefly stage will be attacked, this beetle prefers nymphs and eggs. As many as 12 big nymphs or 160 eggs can be consumed by adult predators daily. Delicatus can control all whitefly species and work well in conjunction with parasitic wasps.

In order to reproduce, high levels of whiteflies in different stages are necessary for delicatus beetles. You should release approximately 100 beetles for every 10 plants located in a hot spot. Tips for introducing delicatus :

  • Beetles can be refrigerated for a maximum of 12 hours before introduction
  • Beetles should be introduced either in the evening or early morning hours
  • Before releasing the beetles, use clear water to lightly mist your foliage
  • Introduce beetles as close to a high whitefly density as possible
  • The parasites must feed on the eggs to be able to reproduce
  • To ensure correct mating, at least 10 beetles must be released
  • Release the beetles right onto your infected plants

Amblyseius Swirskii

Amblyseius swirskii is an extremely effective generalist predatory mite that can be used to contain immature thrips, cyclamen mites, two-spotted spider mitesbroad mites, and whiteflies in fruit, ornamental and market crops.

Adults are pear-shaped, 0.5 mm long, with long legs. The eggs are transparent and round and 0.14 mm in diameter. A. swirskii lay their eggs on leaf hairs and along the veins on the inner surface of leaves. Eggs hatch in about 3 days.

Like other generalist insect predators, A. Swirskii can sustain its population even when food sources are no longer present on the plants and will start working as soon as pests begin to surge. A. swirskii is not susceptible to diapause so it can be introduced in the winter. It is also tolerant of high temperatures. A. Swirskii needs more heat than Neoseiulus cucumeris to develop fully.

The introduction rate provided below is simply suggestive. Specific conditions need to be considered such as type of crop, climate and temperature and the severity of the infestation.

  • Introduce to crop quickly upon receipt
  • Use 25 for every square yard for preventative
  • Use 50 for every square yard for light curative
  • Use 100-300 for every square yard for heavy curative
  • A. swirskii population starts to develop when the temperature regularly exceeds 68-72°F

Defeat Pests, Mold and Mildew… NATURALLY!

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