How to Get Rid of Whiteflies
Updated: May 23, 2023
Whiteflies are a major problem for greenhouse growers. These tiny moth-like pests congregate on the undersides of leaves and and suck the sap from the plant. They are transmit plant viruses.
Despite their name and appearance, whiteflies are neither moths or flies. In fact, they are distant cousins of aphids and leafhoppers.
In this article we're going to discuss:
Signs & symptoms of whitefly infestations
How to get rid of whiteflies
Garden cleanliness & pest prevention
Table of Contents
Whitefly Taxonomy
Early Signs of Whiteflies
Whiteflies on Plants
Whitefly Taxonomy
The initial signs of a whitefly infestation are very subtle and can be easy to overlook. Their surreptitious nature allows them to reproduce undetected until the infestation grows into something catastrophic.
Whitefly infestations resemble aphid damage. Plants lose vigor and leaves begin to droop before turning yellow and wilting.
Leaves may appear waxy with sticky honeydew or sooty-colored fungus that grows on the honeydew.
Adult whiteflies often resemble tiny specks of ash on the undersides of leaves.
Greenhouse whiteflies reproduce year-round.
One way to differentiate between an aphid or whitefly infestation is to shake the plant.
In the event of a whitefly infestation, a cloud of whiteflies will erupt from the plant when the leaves are agitated. If the plant is only infested with aphids, no such cloud will appear.
Aphids, also known as "plant lice," are soft-bodied, pear-shaped pests with long legs and antennae. A pair of tubelike cornicles or siphons project backward from the abdomen, almost like the tailpipe of a car.
Adult aphids are typically measure around 2mm and the rear end tapers to a pointed, tail-like caudum between the cornicles.
Aphids vary in color from black to green and some species of aphids are known to have paired bumps between the antennae on the head called "antennal tubercles."
The majority of adult male aphids do not have wings and are called apterae. Adult males that do have wings are called alatae, and their wings are much longer than their bodies.
These winged adults are called spring migrants and fly off to secondary hosts, such as cannabis.
Aphids attack cannabis plants by colonizing the stems and the undersides of the plant's leaves. They puncture the stems, branches, and leaves to suck the sap with straw-like mouths.
Aphids excrete a concentrated sugar solution called "honeydew" that attracts ants who heard and "farm" the aphids, thus protecting them from predators.
Differential Diagnosis
Early signs of whiteflies include wilting and yellowing, can easily be confused with leafhopper or aphid infestations.
That's why it's important to make a positive identification with a 100x microscope before deciding on a course of action.
Turn over the leaf and examine the underside to make a determination.
Early Signs of Whiteflies
Whiteflies congregate on the undersides of leaflets and cause yellowing and wilting.
Adult whiteflies barely measure 1mm in length, making them somewhat difficult to detect, especially in the early stages of an infestation.
Females each lay over 100 eggs on the undersides of leaves. Eggs are pale yellow, 0.2mm long, oval-shaped, and have short stalks that anchor them to the leaves.
Eggs are often laid in circles or semicircles and may appear covered in dust that gets kicked up from the females' wings and will turn purple-grey to brownish-black right before hatching.
Larvae are oval, flat, transparent, and radiate a halo of short, waxy threads from their bodies.
Late-stage larvae lose their legs and appear off-white in color.
Larvae take two to four weeks to reach adulthood and adults live for four to six weeks. In greenhouses, generations often overlap so that allo stages of growth occur simultaneously.
Optimal conditions for reproduction are around 80 degrees Fahrenheit (27 degrees Celsius) and 75-80% humidity.
How to Get Rid of Whiteflies
Whiteflies are attracted to yellow objects so deploying yellow sticky traps will make them easier to detect and will help to remove adults from the population.
Sanitation is key, particularly in indoor gardens.
There is evidence to suggest that ionizers may help alleviate moderate infestations.
You can also suck adult whiteflies from leaves with a low-powered vacuum cleaner.
The ideal time to deploy this method is in the morning when whiteflies are cold and moving slowly.
Avoid planting outdoor crops near eggplant, sweetpotato, tobacco, and cotton. All of these plants attract whiteflies.
Prevention
Indoor gardeners should abide by all generally-accepted cleanliness practices, including:
Wearing decontaminated coveralls over clothing and covering hair when working around or near plants.
Dawning clean shoe covers when entering a growroom
Filtering any air that enters the grow space
It is also a good idea to deploy biological controls preventively.
Biological Control of Whiteflies
Parasitic wasps (Encarsia formosa, E. luteola, & Eretmocerus eremicus) are the best defense against whiteflies.
Other predators include:
Delphastus pusillus
Geocoris punctipes
Macrolophus caliginosus
Pirate bugs
Deraeocoris brevis
Green lacewings
Ladybeetles
For best results, use a combination of parasitoids and predators.
Fungi are the ideal microbial biocontrol because they infect whiteflies on contact whereas other microbials and viruses must be eaten.
Effective species of fungi include:
Verticillium lecanii
Beauveria bassiana
Aschersonia aleyrodis
Paecilomyces fumosoroseus
Metarhizium anisopliae
Whiteflies are repelled by Nasturtium species and shoo-fly.
Chemical Control
Horticultural oil (neem) was determined to be the most effective chemical control against whiteflies in a head-to-head comparison of five different pesticides.
Neem oil also had the lowest impact on biocontrols.
Whiteflies on Plants
Bibliography
J.M. McPartland, R.C. Clarke, and D.P. Watson (2000) 'Hemp Diseases and Pests', CABI Publishing, Chapter 4: Insects and Mites, pp. 39-44
J.C. Stitch (2008) 'Marijuana Garden Saver', Edited by Ed Rosenthal, Quick Trading Company, Chapter 2: Pests, pp. 77-79
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