Dealing with Whiteflies

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Dealing With Those Darn Whiteflies

Solutions: Insect Soap, Rotenone/Pyrethrum Spray,
Seaweed Powder, Sticky Traps, Spinosad

Whiteflies can seem to come out of nowhere all of a sudden! They are easy to identify. When you move or water your plants and you see what looks like an instant snowstorm with minute things flitting all over, you've got whiteflies! At the first sign of them you want to take action as they multiply like crazy.

Let's talk a bit about whiteflies and then we'll get to some controls. It always helps to understand the nature of the critter you are dealing with. Although all whiteflies tend to look alike, there are two major types, the greenhouse whitefly and the silverleaf whitefly. Adult greenhouse whiteflies are slightly less than 1/8 inch long. They have a white, waxy coating and hold their wings parallel to the leaf surface. Adult silverleaf whiteflies are a bit smaller than the greenhouse whitefly and they have a yellowish hue to them. They hold their slim wings at a 45-degree angle to the leaf surface. Whiteflies are not true flies as they are relatives of mealybugs, scales and aphids. The eggs are laid on the undersides of leaves. They are cone-shaped and range in color depending on species from from dark gray to burnt orange. The eggs are often laid in a circular or crescent pattern. If you see them, smash them. When the eggs hatch in 4-12 days what emerges is a white, flat, oval shaped nymph. They have no legs and can be mistaken for scale insects at times.

In more northern climates silverleaf whiteflies that have plagued us outside will die after a hard freeze. In the south the silverleaf whiteflies overwinter in the milder areas and come forth in spring when temperatures are consistently 65 F and above. We often bring home plants from greenhouses and nurseries, which have the greenhouse whiteflies.

It is the nymph and adult fly that cause physical damage to the host plants. They attack the leaves, buds and stems sucking the juice out of them. Without control infested plants will turn yellow, growth become stunted and ultimately die. Whiteflies produce honeydew (like aphids) that drips onto the plant encouraging the growth of sooty mold and they can spread plant viruses. Now we understand a little more about whiteflies and it’s time to get to the controls. These techniques may be used inside or out as you see fit.

Monitoring Devices

Nicotiana AKA flowering tobacco will attract whiteflies making it useful as a trap crop and an early warning plant.

Yellow sticky traps, which we carry, can snare the first whiteflies to emerge giving you the red alert and are very useful for greenhouse and home monitoring. To a degree they will also help control the population. For best results hang or place the cards close to the top of the plant. For the home and greenhouse: doors, vents and other openings where whiteflies can enter are also good sites to hang yellow sticky cards.

Whitefly Predators as follows

Ladybug (Delphastus pusillus): those hard working friends of gardeners! The ladybug larvae will consume up to 1000 whitefly eggs in its lifetime but also feeds on nymphs.

Green Lacewing (Chrysoperla spp.): the most voracious, effective predator.
Trichogramma wasps

Encarsia formosa: a tiny golden wasp which is a parasitoid meaning it actually kills its host. The best time to use Encarsia is between mid-March and mid-September. They are most effective on the greenhouse whiteflies.

Predatory mites (Euseius spp.)

Songbirds including phoebes, swallows and kinglets feed on whitefies.

Preventative Measures

Use a seaweed spray to mist the leaves of your plants. Along with all the benefits plants derive from a seaweed spray it also seems to make the foliage undesirable for whiteflies to reproduce on. Spray garden plants in spring, houseplants at least a week before bringing inside and use in the greenhouse for seedlings and as needed. Try our Seaweed Powder.

Insecticidal soap: White flies are soft-bodied insects and can be successfully controlled and prevented with insect soap sprays. Try Insect Soap for whiteflies.

Repellant plants: African, French marigolds (Tagetes), Calendula, nasturtiums, and Peruvian cherry.

Shoofly plant traps whiteflies on it leaves making it a perfect choice to control and monitor the little devils in the greenhouse or home.

Direct Controls

Use a vacuum to carefully suck up as many whiteflies as you can. Insect or dustbuster units are ideal.

Here's a recipe for whiteflies to try:

Mix 1 tablespoon of insecticidal soap, 1 cup of 70% isopropyl alcohol and 1 quart of water. Proceed to spray at least 2 times 7 days apart. Spray heavily to the point of runoff. Do not breath the mist of this as the isopropyl alcohol is poisonous. When used with care it can be effective. Do test for alcohol sensitivity on plants as isopropyl alcohol will dissolve the natural coating on plants that have waxy leaves. Do not use on seedlings. Though not as strong and more expensive, vodka may be substituted for the isopropyl alcohol.

Whiteflies cam be an indicator of phosphorous and magnesium deficiencies. You can correct magnesium deficiencies by mixing 4 ounces of Epsom salts with 1 gallon of water. Use as a soil soak for infested plants. We won't say that this is a cure all but it can certainly benefit your plant especially tomatoes and peppers.

For the greenhouse and possibly inside: use a yellow light bulb which attracts the flies and toasts them like a bug zapper. Unlike a bug zapper beneficial insects that might be in the greenhouse are not fried by the yellow light.

Last resort: Pyrethrum Spray a botanical poison, paralyzes them on contact. The key to using this product is to directly spray the target pest. This would be the under and upper surfaces of the leaves where they congregate. Making 2 applications 3 to 5 days apart should give control.

Use rue or eucalyptus, making a very strong tea from them. Then apply this as a spray against the adults.

Light horticultural oil can be used as a spray to suffocate the flies indoors and out.

Alcohol spray: Mix 4 ounces of 70% isopropyl alcohol to 12 ounces of water and spray. Again test for plant sensitivity as alcohol can burn. Don't use on plants with waxy or hairy leaves.