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The RQS Blog

Cannabis And Whitefly: How To Control And Prevent Them

Whitefly affects cannabis growers and regular gardeners around the world. Read on for a detailed look at this common garden pest and how to control/prevent an infestation in your garden.

18 Jan 2023

By Steven Voser

Contents:

Signs of a cannabis whitefly infestation
How to treat whiteflies on cannabis
How to prevent a whitefly infestation on cannabis
Whiteflies: an unwelcome guest
How to deter large insects
Shield your weed from small insects
Keep your crop safe from hungry animals

Whiteflies are among the more troublesome little critters that you might find feasting on your cannabis plants. Though tiny, they can cause real damage and endanger your whole crop if left untreated.

In this article, we investigate what whiteflies are, how you can spot them, and what to do about them.

What Are Whiteflies?

Whiteflies are tiny insects that feast on the sap of plants, including cannabis. Though tiny—<0.1 inches long—an unchecked whitefly infestation can cause serious harm to a weed crop.

There are in fact about 1,500 different species of whitefly, with the most common (in relation to cannabis) being the greenhouse whitefly—Trialeurodes vaporariorum. Whiteflies breed fast and in large numbers, which means controlling them is sometimes difficult once an infestation has taken hold. Nevertheless, with a little perseverance, there is plenty you can do to save your grow.

What Do Whiteflies Look Like?

Whiteflies can vary in appearance, with one of the major differences being that some species only have two wings while others have four. For reference, the greenhouse whitefly has four wings that lie folded alongside the body when at rest.

General whitefly characteristics include:

Females are usually between 1–0.1 inches long; males are even smaller
Wingspan is less than 0.1 inches
Two eyes; one on each side of the head
Two antenna
Generally white in color—as the name suggests—though some can be different colors
Whiteflies appear dusty as they are covered in a fine wax powder
Six pairs of legs, with the final pair often hidden beneath wings

The Whitefly Life Cycle

These creatures live and breed fast. Adults lay very many eggs, in clutches of around 80–300. Eggs take 6 days to hatch. After hatching, they go through four different developmental phases, which in total take 28 days. After this period, they are fully mature and capable of reproducing.

Signs of a Cannabis Whitefly Infestation

Whiteflies leave various indications of their presence on your plants. First and foremost, you might be able to see them moving around, in which case there is no doubt about their presence! Second, clutches of eggs are a sure indication that something undesirable is present.

Others signs are:

Yellow or translucent marks on the surface of leaves (from feeding).
Honeydew: This is a sugary waste product of whitefly feeding. In order to extract enough protein from the plant, they need to eat a lot of sap. Then, they excrete most of the sugars back onto the leaves. This residue can attract sooty mold, which is very dangerous.
If you notice ants crawling over your plants, they may also have been attracted by the honeydew. This is doubly problematic as ants fight off whiteflies' natural predators.

Where Do Whiteflies Lay Eggs?

Whiteflies lay eggs on the underside of plants. Generally, they lay in a spiral or arc pattern. Eggs are usually white, and the pupae that emerge from them are transparent and almost invisible.

How to Treat Whiteflies on Cannabis

Whiteflies are notoriously hard to get rid of, partially because they develop and breed so quickly. As with all infestations and illnesses, acting fast is key. As soon as you see signs of whitefly infestation, take action! They won’t go away on their own.

Pruning and Hosing

Once you've addressed the environmental factors that might be contributing to your whitefly problem (more on this in the next section), it’s time to prune any infected leaves. Make sure to discard any prunings immediately to avoid infecting other plants.

You may want to try hosing down your plants. However, whitefly eggs are notoriously hard to remove from marijuana plants and might require a decent bit of water pressure, which could damage your crop.

Introduce Beneficial Insects

Ladybugs, lacewings, and predatory mites prey on whiteflies and their eggs. If you haven’t already, we highly suggest introducing these insects into your grow environment as they’ll help you control a wide variety of pests (including spider mites).

We suggest beginning with ladybugs, as these are some of the most ferocious insect predators out there. You can even buy them in tubes from garden centers. They tend to disperse within a day or two, though, so it might take several batches to fully eradicate a whitefly infestation.

Spinosad

All spinosad products are completely organic. We suggest spraying plants directly to kill any flies upon contact, as well as adding some during watering to help fend off whiteflies and other pests in the future.

These compounds are found in naturally occurring bacteria, and are great for dealing with certain pests (such as whiteflies) but do little harm to other animals. For large animals and humans, it is considered harmless. Moreover, it fully breaks down within 24 hours, meaning that it won’t harm the wider environment. However, a couple of applications might be necessary.

Insecticidal Soap

Insecticidal soap is great for spot-treating infected areas of your plants. Try not to get it directly on any buds, and consider using it multiple times to ensure you’ve killed off all the flies in your grow area.

You can make anti-whitefly soap at home by mixing 10ml of household soap with 1 litre of water. Then, use a misting bottle to spray this onto your plants’ leaves—both the tops and bottoms. It is certain that multiple applications will be necessary in order to properly remove an infestation.

Neem Oil

Neem oil is a favorite among organic growers, in cannabis cultivation and beyond.

This is a potent, naturally occurring insecticide. While the other solutions are a little hit-or-miss, neem oil provides a solid solution that should fix an infestation without damaging the wider environment too much. However, be aware that it will damage most insects, and is thought to potentially be harmful even to humans if ingested.

Note: Insecticidal soaps soften insects' outer shells, making it easier for insecticides to work. So consider using an insecticidal soap around an hour before applying neem oil to make it more effective.

How to Prevent a Whitefly Infestation on Cannabis

If you can, it’s best to not have a whitefly infestation in the first place. Though impossible to avoid entirely, there are a few steps you can take to make infestation less likely.

Clean the Grow Space

Before bringing your plants into a grow room or greenhouse, clean everything thoroughly and try to get the space fairly sterile. This means that there won’t already be whiteflies waiting for them.

Control the Environment

Whiteflies like warm weather and thrive in conditions where there are no (or few) predators around. Therefore, it’s important to make sure that your grow room is free of dust and any other insects that might naturally interfere with whitefly predators (such as ants). Also, make sure your grow room temperatures aren’t too high (20–25ºC or 68–77ºF is ideal).

If you’ve noticed some whiteflies in your grow room, you may want to bring temperatures down a little to fend off a bigger infestation. Aim to temporarily bring the temperature down to slightly below 20ºC or 68ºF, but be careful not to subject plants to temperatures below 16ºC or 60ºF.

Finally, make sure your grow room is well-ventilated. This is an important step in fending off most garden pests, which tend to love stagnant, humid environments.

Preventative Spraying

Some growers, especially those with large crops in greenhouses or outdoors, will spray their plants with neem oil every 20 or so days to prevent an infestation. If you have a small grow, this may not be necessary, as you can deal with problems as they occur. If, however, you have many plants, a preventative neem oil treatment can avert disaster.

Sticky Traps

Hanging sticky traps around your plants from day one can help to ward off an infestation. Hopefully, these will attract any errant whiteflies before they reach your plants—and stop others from ever reaching your plants.

Used alongside other measures, sticky traps can be very helpful.

Whiteflies: An Unwelcome Guest

Whiteflies are really not an insect you want living on your plants. Between their feeding and their excreting habits, they can cause a lot of damage for such small creatures.

If you’re growing outdoors or in a greenhouse, using the preventative measures above can make your life much easier in the long run. If you’re growing indoors, then you’re probably okay to just keep an eye on your plants, and act accordingly if and when you discover an issue.

Whichever route you opt for, if you do find signs of a whitefly presence, act fast!