Cannabis Pests - Whiteflies

Whiteflies are a common pest that many outdoor growers have a constant battle against every year. Although whiteflies can mean disaster for your cannabis plants, if we act quickly there treatments that can efficiently solve this annoying pest. This guide teaches you how to spot an early whitefly infestation, in addition to the right treatments for destroying them as soon as possible.

What Are Whiteflies?

Whiteflies are not actually flies, but belong to a group of insects called Hemipterans. They make up the family that goes by the name Aleyrodidae, which forms part of more than 1500 species of whitefly. 

Whiteflies look like tiny white moths that measure roughly 1-2mm in length. With closed wings they have a oval/triangular shape but with their wings open the span is about 3mm. They live on the undersides of leaves, where they lay their eggs and feed off the sap but puncturing the soft outer tissues. This damage eventually becomes noticeable on the tops of the leaves. Although small, these flying bugs can develop in huge numbers and drain your plants of nutrients.

Whitefly move quickly and are easily noticed flying around the infected plant during the daytime. Their numbers can grow rapidly, with each female whitefly able to lay around 100-200 eggs during her lifetime. The eggs are snug in place and not washed off easily.

R#7 GSC from Auto Seeds

The eggs hatch into crawling nymphs which find a place to feed and then eventually lose their legs as their pupa stage begins, which has 3 phases until it finally becomes an adult. Left unchecked, and whiteflies can be a serious problem for all types of agriculturalist, including the ganja farmers.

The Causes of Whiteflies

Whitefly can be predominantly found in hot, tropical climates and are particularly problematic in greenhouses where they are protected from predators. However, whitefly infestations can get so bad in some places that they can even withstand extreme cold conditions, allowing them to breed all year round. 

Because of their small size, whiteflies are able to find their way into indoor spaces their predators cannot, giving them the perfect opportunity to establish a colony. Whitefly live for just 3 weeks, meaning things can escalate very quickly when the conditions are favourable.

Depending on the exact species, whiteflies are attracted to a variety of different host plants, including lettuces, tomatoes, peppers, eggplants, hibiscus, geraniums and poinsettia, amongst plenty of others. On top of that, they are known to transmit plant viruses easily.

Identifying Whiteflies

Like aphids, whiteflies leave behind a sweet, sticky excrement known as honeydew. This can cause sooty mold to form, further weakening the leaves by preventing them from photosynthesising correctly.

Heavily affected leaves get completely drained of nutrients, turn brown and fall off. An overall decline in plant health becomes clearly noticeable.

Symptoms of whitefly infestation:

• Wilting and yellowing leaves (chlorosis)
• Slow growth
• White spots on topside of leaves
• Tiny, white eggs, sometimes in circular formations underneath leaves
• Honeydew excrement
• Sooty mold
• Ants.

Whitefly Treatment

Treating whiteflies is a challenge as they can quickly develop a tolerance to insecticides and other chemical pesticides. Depending on how severe the infestation is, multiple treatments are likely to be necessary. Some treatments work best for killing off eggs and nymphs, other are better suited for adults. Let's take a look.

Remove affected leaves - Because of the way whiteflies cluster themselves together, parts or whole leaves can be removed and burned or placed in a bucket of warm soapy water to kill the eggs and larvae. Pruning is the most direct way of removing whitefly young but it is unlikely to eradicate them completely and you want to be careful not to harm your plants further by removing too many leaves while they are infected. Also, clean up any dead leaves that might be lying around as nymphs could still be feeding on them.

Clean the plants - Blasting your plants with a hose can do a good job of scattering the whiteflies and help to loosen the eggs and nymphs 'fused' to the undersides of the leaves. Just be careful not to use too much pressure as it may damage the plants.

Predators - Green lacewings (Chrysopa), lady bugs (Delphastus) or predatory mites (Phytoseiidae) are known to feast on whiteflies. Just make sure you are not using any sprays at the same time otherwise you may kill the beneficial insects. Apply predators instead of or after any insecticide has been used. Other biological control bugs that can destroy whiteflies are Encarsia formosa, Eretmocerus eremicus, and Delphastus catalinae.

Neem Oil - Neem oil can really help to keep the populations down and stop whiteflies spreading so quickly. The adults won't want to land on the plants after spraying and the nymphs eventually ingest it, killing them. Neem oil is strong and may even deter predatory insects that could be beneficial for killing the whiteflies, so be careful how and when you use it. Dilute with water and potassium soap for an effective treatment. Apply 2-3 times per week, making sure not to spray on any flowers.

Insecticidal Soaps - Insecticidal soaps work well for all sorts of cannabis pests, and can be used effectively against whiteflies. They are completely safe but best not to spray on buds. You may need to apply most insecticidal soaps every day or two as they do not stay on the plant for long. If you are using with neem oil, spray less frequently. Check the label for further instructions on dilution or strength.

Spinosad and Essentia IC3 - Both of these work as effective organic insecticides against whiteflies. Use either one but preferably not both unless you have already tried one and not seen an improvement. Multiple applications are likely to be necessary but once consumed by nymphs and adults they can eventually die off. Avoid spraying on the flowers.

Tips For Preventing Whiteflies

It goes without saying that prevention is always the best solution to any potential pest problem. Keeping your grow environment as clean as possible is key, as is maintaining a suitable environment that does not put your cannabis plants at risk.

Tips for preventing whiteflies:

• Maintain temperatures below 25°C
• Use high quality soils.
• Add a few yellow adhesive strips around your plants to catch infestations early.
• Keep any new plants you bring into the grow space isolated for at least a week to make sure they are not infected.
• Use screens over ventilation holes.
• Apply neem oil preventative foliar spray once per week (during lights out) throughout vegetation.
• Introduce biological pest control before any signs of whiteflies (if you are not using sprays).

You can try bringing the temperatures down to around the 20°C range while you apply treatments as it may further discourage the whiteflies from staying on the plants.

Check out Cogollo_eu's Girl Scout Cookies (Fast Buds) diary to see more on combating whiteflies.

If you found this article useful or have any tips regarding whiteflies and their prevention or treatment, please share your thoughts with the community in the comments section below!

External References

An annotated check list of the world's whiteflies (Insecta: Hemiptera: Aleyrodidae). - Martin, J.H.; Mound, L.A. (2007)

Potential of the predatory mite Phytoseius finitimus (Acari: Phytoseiidae) to feed and reproduce on greenhouse pests. - Pappas, M.L., Xanthis, C., Samaras, K. (2013)

Transmission of Viruses by Whiteflies. In: Characterization of Plant Viruses. - Bhat A.I., Rao G.P. (2020) 

BIOLOGICAL CONTROL OF WHITEFLY BY SPECIES OF LADYBUG Delphastus spp.. - Giraldi, Greissi & Guerreiro, Julio & Augusto, Cawana & Pessoa, Thainara & Santos, Luiz & Silva, Paulo & Ferrari, Diogo & Silva, Keli. (2020).

Whitefly Endosymbionts: Biology, Evolution, and Plant Virus Interactions. - Andreason, Sharon & Shelby, Emily & Moss, Jeanette B & Moore, Patricia & Moore, Allen & Simmons, Alvin. (2020).

This article was updated December 2020.