How to control Whiteflies on marijuana plants

What's the Whitefly?


Whiteflies are hemipteran insects of the Aleyrodidae genus that attack many types of cultivated plants, including cannabis crops. These flies are about 2 mm in length and have a whitish appearance, with a pair of wings that serve as displacement method. They're usually found on the underside of the leaves (where they also lay their eggs, as we're going to see later) and, like other sucking insects such as Aphids or Mealybugs, they feed on sucking the sap of the plants.

Their body consists of three parts: the head, thorax, and abdomen. Like other insects, they've six legs and also a pair of white wings. As already mentioned, they've biting-sucking mouth parts thanks to which they can feed on the sap of young leaves and tissues.

Reproduction of the Whitefly

This insect reproduces through eggs, which it lays on the underside of the leaves in a quantity of 180-200 in each egg laying. These eggs are almost microscopic, of oval-pyramidal shape, and with a yellowish-white color. They've usually four generations a year (one generation is the duration of the insect's life cycle from the egg until it dies like an adult) depending on climatic conditions and hygiene, although in the greenhouse they can have up to ten per year, turning so into a serious pest.

Reproduction of the Whitefly, egg laying
Reproduction of the Whitefly, egg-laying

It is a pest that likes high temperatures and relatively humid ambient, that's why the summer is their favorite season and greenhouses and grow tents their favorite habitat. From the egg laying until the birth of the larva they spend approximately 24 hours: then the larva needs less than four weeks to become an adult, passing through 4 larval-nymphal stages in flake form and located on the underside of the leaves.

  • First stage: Approximate size of 0.25mm. The larva feeds on sucking sap from the plant. Only in this stage, the larva is capable of moving, the other three are sessile, i.e. the nymph is enclosed in a capsule to protect itself while its structure changes.
  • Second stage: Approximate size of 0.4 mm. The formation of six legs can be seen on the larva.
  • Third stage: Approximate size of 0.5 mm. Transparent appearance.
  • Fourth Stage: Some organs, like the eyes, appear at this stage. Its thickness and size increase. Normally, this nymphal state is called "pupa"; the adult emerges from its protective capsule through a T-shaped slot - normally in the morning - starting to fly immediately.

Symptoms and damages caused by the Whitefly

White-Fly plague
Tremendous Whitefly pest infestation

The first evidence of the attack of these insects is chlorosis, deficiencies (yellowing) in the leaves, which end up drying - usually starting at the edges - and falling. The plant often suffers a slowdown in its development and a general deterioration of its state.

Apart from the symptoms caused directly by its sap-sucking action, other symptoms related to the sugary honeydew secreted by these insects may appear, which favours the appearance of sooty mold, a black fungus that stains the leaves and weakens the photosynthetic process. It may also appear with other diseases, viruses, and bacteria.

Keep in mind then - especially when you're treating with a flying insect that has ease for the displacement - that whiteflies can cause serious damage to a crop, not only by its sap-sucking action but also by the diverse diseases that can be transmitted to the plants, for whiteflies are a vector insect of these.

Prevention and control of the Whitefly

Basil aroma repels the White-Fly

As in most pests and diseases that may affect the different strains of marijuana, prevention is basic to reduce the chances of possible attacks and infections. We can rotate our plants with others, thus creating an association of beneficial plants: growing Marigolds, Chinese Carnations, or Basil will help to prevent the appearance of whiteflies because their smell repels them. We must check the underside of the leaves regularly looking for adults or larvae, and use an organic insecticide like potassium soap or Neem oil every few days. The use of sticky traps, in which adult insects will be stuck, will make things more difficult for them.

If we already have an affected crop we can use different ecological remedies to combat the plague: Rotenone and Pyrethrins (commonly used in organic farming as an alternative to chemicals) work well, and their use can be alternated with other insecticides such as infusions of Tansy or wormwood.

Macrolophus Caliginosus
Macrolophus Caliginosus, natural predator of the White-Fly

If these remedies don't work - or if we don't want to use them for any reason - we can combat the White-Fly with different natural predators.  Some of the most effective ones are:

  • Cales Noacki: Small wasp that parasites whitefly larvae. Very effective, although it isn't commercialized on the market.
  • Encarsia Formosa: especially effective in greenhouses. Small fly of just 1mm of black color with transparent wings. As the Cales Noacki, it lays its eggs (parasites) in White-fly larvae. It reaches its maximum predatory efficiency at a temperature of 25-27ºC and 50-60% relative humidity, using 10 predators per m2.
  • Macrolophus Caliginosus: useful also to combat other pests like spider mites. They attack Whiteflies in all their stages, preferring eggs and larvae.
  • You can also use other predators, like fungi: Paecilomyces fumosororeus, Beauveria Bassiana, etc.

As a last resort, and always avoiding their use for the sake of our environment, we can use chemicals to eradicate a Whitefly pest. These treatments will be especially effective against the larvae, which tend to be more sensitive to these substances. It should be noted that Whiteflies have a great capacity to develop defenses against these products, so we should alternate the use of several active principles to get maximum effectiveness. We should always choose insecticides respectful with the natural enemies of the plague that we are going to treat, limiting their use to the most and always as last resource, since a biological crop is always better.

As active substances against the Whitefly, and among others, we find Butocarboxim, Buprofezin, Imidalclopid, etc.

We hope to have helped you in the fight against this annoying pest, remember that perseverance in prevention and hygiene are the keys to preventing the emergence of any pest or disease in your plants. We wish you happy and prosperous crops!

Good Vibes!

The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “How to control Whiteflies on marijuana plants” (7)


jellyman 2020-11-19
I have a bad infestation of whiteflies in my multi plant rooms. When I sprayed with neem oil/water mixed (in darkness) and then rinsed the leaves with plain water that next morning just as the lights turned on all the plants I sprayed burned up and now they are stunted even more. Its been almost two weeks and I'm still killing them by hand in the flowering room after the neem ruined one plants buds, and I removed all the effected parts off the veg plants tonight. I am wondering if pyrethrin sprays would also burn my plants leaves even after rinsing with water. my LED lights are dimmable and I even dimmed and raised them to "lower" the light in the room. If anyone has some insight please help!

Alchimia Staff

Tim Alchimia 2020-11-20
Hi, thanks for your comment and question. You definitely did the correct thing by dimming the lights but it sounds like the neem oil solution that you mixed was too concentrated for the plants and burned them. I use neem frequently and I've never seen any damage to leaves in 15 years of use. To make a gallon of solution, I mix 10ml Neem Oil with 10ml Potassium Silicate in a small bottle, shake well to emulsify and then add this mix to a gallon of water, along with 5ml of insecticidal soap, which helps as a de-surfactant during application. I sometimes add essential oils like lavender, eucalyptus and peppermint (4-6 drops of each per gallon), which, as well as helping to dissuade insect pests, really helps to improve the frankly disgusting smell of Neem Oil! One more important point to remember, and I bring this up because you mention that the neem ruined some buds... you should never use neem oil on flowering plants, ever. This isn't because of any damage to the plant, but because it will make your flowers unsmokeable when you harvest them. It should only be used in vegetative growth because the oil will adhere to the flowers and not only ruin the flavour but can be a potential health hazard if smoked too. For the record, rinsing the plants with clean water the next day will remove some neem oil residue but not much. The same goes for pyrethrin, which is now prohibited for use on cannabis in the US, I might use some on young seedlings or clones but it should never be applied to flowering plants. If your plants are in flower, then really the only safe option for dealing with a Whitefly infestation would be a combination of ambiental controls (lowering the temperature to slow reproduction, improving ventilation) alongside natural predators such as Wasps, Ladybugs, lacewings or predatory mites. I hope that helps, best wishes and happy growing!


Viv 2019-07-07
My plant looks like a fungus happening no white mildew just looks like a roughness on the leaves. Not white. Just no5 bright green. Dull in color like.

Alchimia Staff

Tim Alchimia 2019-07-08
Hi Viv, thanks for the question, it's hard to know exactly what the problem could be, I've had plants with rough textured leaves, and sometimes it's been down to a health problem while other times it's just a slight mutation in the genetics and the plant grows out of it. In your case I'd recommend spraying the plants with something that will serve as a general purpose fungicide but will also work to stimulate the plant and encourage good health. Products like Cannacure and Super Kukulus should fit the bill. All the best with this, please let us know how the plant progresses. Happy growing!

avatar 2018-09-08
Small vacuum cleaner will do it under each leaf


Dianne Houde 2018-08-04
So if i soray thr leavse with peppermint oil do i mix it with water?

Alchimia Staff

Tim Alchimia 2018-08-06
Hi Dianne, thanks for your question. Yes, you'll need to mix the peppermint essential oil with water. Use 1 drop of essential oil per 60ml of water and add a tiny bit of dish soap to help better spread the mixture over the leaves when you spray them. Have a look at our article on Foliar Spray basics for more tips on spraying correctly. Hope that helps, happy growing!


June Hutchison 2018-07-14
Thank you, I will try the cinnamon extract with Castile soap in a spray bottle, but my question is how many times a week?? And should I spray in the evening when the plant's are not in the direct sun???

Alchimia Staff

Tim Alchimia 2018-07-16
Yes, that's right June, either in the morning or in the evening, but always spraying when the plants aren't in direct sunlight. All the best!


shootthatgagmywayace 2018-02-24
i have been fighting whitflies with neems oil and insecticidal soap with poor results. They never completely go away and kill my plants one by one. i noticed when digging into soil that i see that i see a few flies that seem to be just beneath the top layer of soil. the temp is 20.2 celcius and humidity is 47%. Why cant i get rid of these pest? i alternate sprays every couple days and you cant really find them unless i dig around plants. Any help would be appreciated.

Alchimia Staff

Tim Alchimia 2018-02-27
Hi, thanks for your question. I've got a couple of ideas that might help, but as I imagine you've discovered, you'll need to take a multi-pronged approach, (IPM or Integrated Pest Managnement) as no single measure will be effective on its own: Firstly you can remove them manually, with a water hose, or with the help of a small vacuum cleaner. This is very effective for adults and larvae but the eggs can be more stubborn. Try adding some essential oils (a few drops per litre) to your neem/insecticidal soap mix, I've had good results against spider mites with Rosemary and Peppermint oils, and Eucalyptus, Rosemary, Lemon and Cinnamon are recommended against whitefly. Remember to spray for at least 4-5 weeks to be sure to catch all the stages of the pests life cycle. Another idea is to lower temperatures below 20ºC (without damaging our plants) to create a more hostile environment for the pests. Whitefly are attracted to the colour yellow, so hanging some yellow sticky traps can help to control numbers. If you're finding them in the soil then try using a reflective mulch (aluminium or silver polyethylene) to help with that. This is a common measure in large scale commercial operations. Companion planting of some beneficial flowers like nasturtiums and marigolds can help to keep whitefly away. We can also look at introducing some kind of biological control to deal with the problem, for example these Macrolophus Pygmaeus insect predators are effective against whitefly and many other pests. Predators like Ladybugs and Lacewings are easy enough to find, as well as a wide range of other suitable predators that are widely available to buy these days. I hope thats given you a few ideas, we wish you the best of luck getting rid of the problem. Happy growing!


Andi320 2015-09-07
does hydrogen peroxide work as a foliar spray?

Alchimia Staff

Dani Alchimia 2015-09-08
Hi Andi320, You have better products to combat whiteflies such as Expeléx or Mittel. Hydrogen peroxide is usually used in the reservoir to eliminate algae or to combat root fungi. In rare cases, it is used via foliar to combat powdery mildew (although other products work better). All the best!

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