Whiteflies: How to Destroy This Marijuana Plant Killer

Experienced marijuana growers realize that whiteflies are a curse to their cannabis crops. This particular pest removes sap from leaves, hinders photosynthesis, and, over time, causes cannabis plants to perish.

Whiteflies can lay a staggering number of eggs in a short period of time and can withstand attacks involving chemical pesticides and insecticides. Fortunately, there are organic ways to defeat this pest, and this article identifies these solutions and explains how to use them.

First, let’s learn a little more about whiteflies and why they’re such a problem.

What Are Whiteflies?

Whiteflies are winged insects with soft bodies that feast on plant sap. If you allow an infestation to linger for too long, your plants could die! There are over 1,500 identified species of whiteflies, and these Hemipterans tend to snack on the underside of your leaves.


They have a triangular shape and can be as small as 1-2 mm. Although there are a huge number of whitefly species, they primarily affect a relatively small number of plants. Unfortunately, marijuana is among them! The silverleaf whitefly is one of the most common species in the southern part of the U.S.

How to Spot a Whitefly Infestation

First and foremost, it’s important to note that whiteflies don’t survive cold winters outdoors. Therefore, they’re mainly a problem when you grow marijuana indoors or in a greenhouse. If you live in a milder climate with a warmer winter, whiteflies can survive and even reproduce outdoors all year around.

When whiteflies attack your plants, they suck up plant juices via their mouths. The result is honeydew, a sticky substance that can result in diseases such as mold forming on leaves. This honeydew is a telltale sign that there’s a whitefly infestation. To make matters worse, it attracts ants!

This predator prefers to feed on new plant growth, so look for leaves that have recently unfurled. Look at the undersides of leaves, particularly around the veins, and you may see the movement of white insects. You should also touch the leaves to see if you can feel the honeydew.

When feeding, the whiteflies will fly off the leaves in swarms when disturbed, which may cause a fright!

It’s also important to check for the eggs laid by whiteflies. After hatching, the larvae resemble small ovals with no legs. Even though they don’t begin moving right away, they do begin sucking sap from the plant. This is one of the reasons why so many marijuana growers miss whitefly infestations initially.

What Can Whiteflies Do to Your Marijuana Plants?

As I mentioned earlier, the honeydew produced by whiteflies can ruin your cannabis plants by causing a black sooty mold. This substance deprives your leaves of light over time.

If left alone, the infestation will quickly suck the sap from your plants’ leaves. Eventually, they become so weak that photosynthesis could prove impossible. You may notice that the leaves turn yellow, and the plant’s growth will slow down markedly. Leaves will shrivel and fall off the plants. Eventually, if things get really bad, plants will die.

Here is a quick overview of the life cycle of a whitefly when the temperature in your indoor grow room is approximately 70 degrees Fahrenheit:

  • Egg Hatch: 6-10 days
  • Nymph I: 3-4 days
  • Nymph II: 4-5 days
  • Nymph III: 4-5 days
  • Pupa: 6-10 days
  • Adult: 30-40 days

The warmer the temperature, the faster the transition from egg to adult. A female whitefly can lay up to 400 eggs during its lifetime. As such, an infestation can get out of hand at terrifying speed.

What Chemical Insecticides Are Effective Against Whiteflies?

Various chemical controls are available to destroy whitefly infestations. Imidacloprid is marketed as a low-toxicity option that affects insect neurotransmitters. It has systemic properties and is normally mixed with water and applied to the base of cannabis plants. The roots absorb the insecticide, and it should get to work relatively quickly.

You should avoid using imidacloprid during the flowering stage. Indeed, it’s best not to use it more than a month before you switch the lights to transition from vegging to blooming.

Pyrethroids such as permethrin have been used in the past. However, permethrin was banned because it was shown to be highly toxic to various aquatic organisms.

In general, most chemical insecticides are ineffective against whiteflies because these pests are highly resistant to them. Also, whiteflies in the egg and pupal stages can survive insecticides that may kill nymphs and adults. Therefore, you need to apply such products several times to get the desired results. This is not good news for the taste and quality of your weed!

Can Organic Insecticides Work?

Yes. Natural options, such as neem oils and insecticidal soaps, can help kill whiteflies. Such products are better for your plants and are also a great choice if you have children or pets in the house.

Neem oils suffocate whiteflies, although you have to be careful when applying them because they can burn or scald your plants. When in doubt, add a small amount of neem oil to a leaf and wait 24 hours to see if it causes damage. These oils and soaps kill insects on contact, so reapplication is necessary.

If you use soap or oil, dilute it with water according to the manufacturer’s instructions and spray it on the leaves. Make sure you reapply at least twice more. It’s a good idea to spray during the evening to avoid spraying beneficial insects or pollinators.

Also, when you see an infestation, begin your attack by spraying water on the leaves to scatter the whiteflies and dislodge eggs and nymphs.

Some growers use a hand vacuum to suck up the pests! If you do this, dispose of them accordingly, which means NOT putting them in your bin!

What Other Options Do I Have?

As is often the case when dealing with pests, biological controls are available. For example, the Encarsia formosa, a tiny parasitic wasp, feeds on whiteflies. It develops inside the nymph whiteflies, killing them within a few days. However, for it to work, the temperature within your grow room must average 72 degrees, even at night.


Eretmocerous californicus is another parasitic wasp species that kills whiteflies. This wasp’s ovipositors puncture the nymphs, so rather than laying eggs, adult whiteflies feed on blood from this wound. The E. californicus is particularly effective in combating the silverleaf whitefly.

It’s worth noting that adult whiteflies are strongly attracted to the colors white and yellow. Thus, it’s worth adding sticky traps in those colors to your cannabis garden. Place them just above your plants or along the edges of plantings. These traps can capture adults and also help monitor changes in the population of whiteflies.

One downside with these traps is that they won’t capture younger whiteflies. As such, you should consider traps as one part of a multi-faceted program.

Quick Whitefly Prevention Tips

When it comes to pest infestations on your marijuana crop, prevention is always better than cure. Here are a few ways to reduce the risk of whiteflies coming to town:

  • Check your soil’s nitrogen level; growing mediums that are high in N can attract whiteflies
  • Check for pests before you transfer your plants from one room to the next
  • Consider keeping natural predators, such as ladybugs, dragonflies, and spiders, around during your marijuana plants’ growing cycle
  • Use aluminum reflective mulch early in the growing cycle; it makes it tougher for whiteflies to find the plants as they are blinded by the reflective surface
  • Prune your marijuana plants and remove the trimmed vegetation from the grow room

Whiteflies Don’t Play Around: Get Rid of Them Today & Save Your Marijuana Plants

Whiteflies can cause serious damage to your cannabis crop if left untreated for any period of time. They can survive many chemical insecticides, and one whitefly can lay hundreds of eggs in a matter of weeks.

Check your plants regularly for signs of infestation, and if you find any, use the tips above to help you quickly and effectively get rid of it. A combination of predatory insects and a natural insecticide like neem oil will often solve the issue, although several applications and constant monitoring are also necessary.

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