How to Identify and Control Whiteflies Effectively
White flies are small sucking insects that have developed resistance to many synthetic pesticides making chemical control difficult. Here’s how to get rid of whitefly using proven, organic techniques.
Common on indoor plants, tomatoes, and in greenhouses, the whitefly (Trialeurodes vaporariorum) is a sap-sucking insect that is often found in thick crowds on the undersides of leaves.
When infested plants are disturbed, great clouds of winged adults fly into the air. Both nymphs and adults damage plants by sucking the juices from new growth causing stunted growth, leaf yellowing, and reduced yields.
Plants become weak and susceptible to disease. Like aphids, whiteflies secrete honeydew, so leaves maybe sticky or covered with a black sooty mold. They are also responsible for transmitting several plant viruses.
In southern and coastal states whiteflies are found year-round in outdoor gardens. In northern areas, year-round infestations are possible only indoors.
Host plants include more than 250 ornamental and vegetable plants. Citrus, squash, poinsettia, potato, cucumber, grape, tomato, and hibiscus are commonly infested.
If you’re noticing tiny, white fly-like insects on your plants, you may be dealing with a whitefly infestation. So, keep reading this complete guide to learn everything there is to white flies and how to control them effectively.
The glasshouse whitefly or greenhouse whitefly – Trialeurodes vaporariorum
What are White Flies?
Whiteflies are winged insects that have soft bodies and are closely related to aphids, mealybugs, and scale since they belong to the order Hemiptera. Even though they are called “flies,” whiteflies are not true flies. However, they do have wings and can fly.
Whiteflies are typically found in groups on the undersides of leaves, are as small as 1/12 of an inch, and have a somewhat triangular shape. They are active during the day and scatter when disturbed, making them more visible than some nocturnal insect pests.
There are hundreds of species of whiteflies, but the majority only affect a few host plants. The most troublesome whitefly species in horticulture are those that affect a wider variety of plants, though.
These species of whiteflies include, among others, the greenhouse whitefly, bandedwinged whitefly, giant whitefly, cabbage whitefly, citrus whitefly, and Silverleaf whitefly.
Common in the southern United States is the Silverleaf whitefly, which is smaller and more yellow than other whiteflies and is so named for its ability to turn squash foliage into a silvery color when it infests it.
Silverleaf whitefly, Bemisia tabaci on the bottom of zucchini
How to Identify White Flies
Adults (1/16 inch long) are moth-like insects with powdery white wings and short antennae. They are easily recognized and often found near the tops of plants or on stem ends.
Wingless nymphs are flattened, oval, and almost scale-like in appearance. After the first instar or crawler stage, they settle down and attach themselves to the underside of leaves and begin feeding.
Whiteflies, like aphids, use their sharp piercing-sucking mouthparts to drink plant sap and make a sticky substance called honeydew. If honeydew is left on leaves by itself, it can cause fungal diseases like black sooty mold to grow on the leaves.
When plants are heavily fed by whiteflies, they quickly become extremely weakened and may be unable to perform photosynthesis. It will cause the leaves to wilt, turn a pale or yellow color, stunt the plant’s growth, and eventually, the leaves may shrivel up and fall off the plant.
The presence of honeydew indicates that whiteflies have been feeding for several days. You might also see ants since the sweet honeydew draws them.
Life Cycle of a White Fly
Young nymphs overwinter on the leaves of host plants. In late spring adult females deposit 200-400 eggs in circular clusters on the undersides of upper leaves.
The eggs hatch in 5-10 days and first instar nymphs, which resemble small mealybugs and are called crawlers, move a short distance from the egg before flattening themselves against the leaf to feed. The remaining nymphal stages (2nd, 3rd, and 4th) do not move.
A non-feeding pupal stage follows and within a week, young adults emerge to repeat the cycle. There are many generations per year. Whiteflies develop from egg to adult in approximately 25 days at room temperature. Adults may live for one to two months.
Note: All of the immature stages are easily overlooked. They are usually pale, almost translucent, and blend with the color of the leaf to which they are attached. Superficially they are similar to several scale insects.
What Plants are Susceptible to White Flies?
Whiteflies feed on a wide variety of plants, including ornamental flowers and warm-season vegetables like tomatoes, eggplant, peppers, and okra. They can also be found feeding on cucumber, sweet potatoes, and squash.
There are some species that are known to prey on citrus trees, sweet potatoes, and plants in the cabbage family. For example, the cabbage whitefly will attack brassicas, including cauliflower, cabbage, and broccoli.
They will eat most common houseplants and ornamental when they are indoors, especially ones with soft, smooth leaves. Some common ornamental plants they attack include hibiscus, poinsettia, fuchsia, petunia, and roses.
Where to Find Whiteflies on Plants
Whiteflies typically prefer to feed on new growth, so look first in the vicinity of any freshly unfurled leaves.
Check the undersides of the leaves, especially around the veins, for white insects that might not be easy to see. You can also feel the surfaces of the leaves for sticky honeydew. If the whiteflies are feeding, they will suddenly all fly off the leaves in a swarm, making their presence known.
On the undersides of leaves, you might also find eggs. This is an indication that an entirely new generation is just getting started.
The larvae, which resemble tiny, white ovals without legs and are born from the eggs, don’t move but begin sucking the plant juice right away. Because of this, gardeners frequently overlook whiteflies until it is too late.
Up to 400 eggs can be produced by adult females, and they usually hatch between a week and a month after being laid. They are typically arranged in a circular pattern. When first laid, eggs are pale yellow, but turn brown just prior to hatching.
Whitefly infestation on cabbage leaf
How to Control White Flies Effectively
- Yellow sticky traps are helpful for monitoring and suppressing adult populations.
- If found, use the Bug Blaster to hose off plants with a strong stream of water and reduce pest numbers.
- Natural predators of this pest include beneficial insects such as ladybugs as well as green lacewings larvae, which feed on their eggs, and the whitefly parasite which destroys nymphs and pupae. For best results, make releases when pest levels are low to medium.
- Hummingbirds are another natural predator that can be useful in controlling whitefly population. We recommend working to create a habitat that attracts dragonflies or hummingbirds that serve as natural enemies for these pests.
- If populations are high, use a least-toxic, short-lived organic pesticide to establish control, then release predatory insects to maintain control. But once beneficial insects have been released, it’s not recommended to use insecticides as white flies are usually resistant and it’ll only kill these natural predators that are helping you control their population.
- Apply aluminum reflective mulch early in the season, especially around vegetable crops such as tomatoes and peppers. The reflective mulch makes it difficult for whiteflies to locate their preferred plant hosts.
- Safer® Soap will work fast on heavy infestations. A short-lived natural pesticide, it works by damaging the outer layer of soft-bodied insect pests, causing dehydration and death within hours. Apply 2.5 oz/ gallon of water when insects are present, repeat every 7-10 day as needed.
- BotaniGard ES is a highly effective biological insecticide containing Beauveria bassiana, an entomopathogenic fungus that attacks a long list of troublesome crop pests – even resistant strains! Weekly applications can prevent insect population explosions and provide protection equal to or better than conventional chemical pesticides.
- Organic Neem Oil can be sprayed on vegetables, fruit trees, and flowers to kill eggs, larvae, and adults. Mix 1 oz/ gallon of water and spray all leaf surfaces (including the undersides of leaves) until completely wet.
- Horticultural oils, which work by smothering insects, are very effective on all stages of this pest.
- Fast-acting botanical insecticides should be used as a last resort. Derived from plants which have insecticidal properties, these natural pesticides have fewer harmful side effects than synthetic chemicals and break down more quickly in the environment.
Note: Ants feed on the honeydew that sucking insects produce and will protect these pests from their natural enemies. An application of Tanglefoot Pest Barrier to the stalks of roses and other woody plants will help get rid of ants.
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