How To Prevent And Kill Whiteflies
One day, all is well in the garden or greenhouse. Then, suddenly, out of nowhere there are whiteflies everywhere!

Good thing is, whiteflies are easy to identify. When you move or water a plant and see little white specks flying around, you've got whiteflies. These pests multiply rapidly so, upon first sighting, you want to take action to quickly and effectively eliminate them.

There are different types of whiteflies but methods for control are generally the same. Whiteflies are not really flies, they are relatives of mealybugs, scales and aphids. Depending on the species, the cone-shaped eggs range from dark gray to burnt orange eggs in color and are laid on the undersides of leaves in a crescent pattern. The eggs hatch into legless, oval shape nymphs that can be mistaken for scale insects. If you find eggs on the leaves squish them!

Both the nymphs and adult fly cause damage to our plants. They attack the leaves, buds and stems sucking the juice out of them. If left alone plants infested by whiteflies will turn yellow, growth will become stunted, and eventually the plant might die. Like aphids, whiteflies produce a honeydew-like substance that is secreted on the leaves, which then encourages the development sooty mold.

Preventing Whiteflies

Prevention is always the first best step in controlling pests. The following techniques can be used to prevent whiteflies.

Insecticidal soap.  White flies are soft-bodied insects and can be successfully prevented and controlled with insect soap sprays. Your local nursery and garden center should carry insecticidal soap products.

Repellant Plants.  There are a few plants that actually repel the whitefly. African and French marigolds, Calendula, Nasturtiums, and Peruvian cherry are a few.

Shoofly Plant.  This plant will trap whiteflies on it leaves of plants that are growing inside the home or greenhouse.

Nutrient Deficiencies.  The presence of whiteflies, especially on tomato and pepper plants, can be an indicator of phosphorus and magnesium deficiency. Epsom salts can be used to correct magnesium deficiencies. You can correct magnesium deficiencies by mixing 4 ounces of Epsom salts with 1 gallon of water and soaking the soil with the mixture. Or, at planting time, you can put a tablespoon or two of Epsom salts beneath the roots of each plant.

Seaweed Spray.  Misting the leaves of plants with a seaweed spray makes them undesirable for whiteflies to reproduce on. Your plants will also receive all the other many benefits fom the seaweed spray. This spray can be used in the greenhouse and garden and also sprayed on houseplants a week before they are brought indoors.

Methods for Control of Whiteflies

Neem Oil - This is our number one "go to" spray to eliminate whiteflies in our gardens. Neem oil is much safer than harsh chemicals to effectively control this pest. Simply mix in a sprayer as directed on the bottle and spray both the tops and undersides of leaves. Make sure to spray again 72 hours later to kill hatchlings. It's best to adjust your sprayer nozzle so that it sprays or fogs rather than shoots a stream. Also, as with any pesticide, to avoid harming butterflies, bees and other pollinators spray in the early morning or late evening hours when these beneficial insects are not active. When dry neem oil will not harm these insects.

Vacuum.  If you catch them early, before serious infestation, you can simply use a vacuum cleaner to suck the whiteflies off your plants. Handheld vacuums are most convenient.

Yellow light bulb.  I've read where a yellow lightbulb can be used indoors or in the greenhouse to attract and then toast the white flies. Unlike with bug zappers, beneficial insects will not be killed by the yellow light bulbs.

Beneficial Insects.  Many insects and birds are natural predators of the whitefly. These beneficial insects often exist naturally in your landscape and garden. Some of the most voracious predators of whiteflies are ladybugs, green lacewigs, Encaria formosa wasps, predatory mites, and birds including: phoebes, swallows, kinglets and hummingbirds. So, put those feeders up to attract these feathered friends and warriors to your garden!

Rue or Eucalyptus.  You can make a strong tea from the leaves of these plants that can be used effectively to control whiteflies when sprayed on the top and undersides of leaves. Spray again every 72 hours until there are no whiteflies.

Horticultural Oil.  This product can be used indoors or outdoors as a spray to suffocate whiteflies.

Traps.  Though not entirely effective in controlling whiteflies, yellow sticky traps can be useful indoors or outdoors as a monitor to let you know if and when whiteflies have moved in. Hang the sticky traps at the top of outdoor plants or near doors, vents or other openings where whiteflies can enter indoors.

Alcohol Spray.  Mix 4 ounces of 70% isopropyl alcohol to 12 ounces of water and spray the foliage of plants. Some plants are sensitive to alcohol and foliage can be burned. Test sensitivity by spraying a leaf or two of a plant and wait a day or so to see if there is tolerance. Plants with waxy or hairy leaves tend to be sensitive to alcohol.

Chemical Insecticides.  We think the use of chemicals should be a last resort when there is heavy infestation. Malathion or Pyrethrins are effective for killing whiteflies. Follow mixing instructions on the product label and then spray both the top and the underside of leaves, where whiteflies hang out. You'll need to spray again every 72 hours (3 days) until there are no whiteflies. When using these products, to avoid harming beneficial insects avoid spraying the flowers of plants and spray in the very early morning or late evening hours when beneficial insects are not active. 

Let me know of you have another good method for controlling whiteflies and I'll add it to the list here.