How to Get Rid of Aphids on Weed

Sophia Delphi May 13, 2022 - 8 min read
Fact Checked
Image of Aphids Crawling on Weed Stem

Sometimes things go perfectly. Other times, the issues seem endless.

That could describe any project from renovating a bathroom to cooking. And when you’re in the middle of something and problems start cascading, you can feel like you’re fighting a losing battle.

A good example? Growing weed plants.

Some grows will be problem-free. During others, you might have to deal with nutritional deficiencies, mold, and insects — and you’re convinced you’ll never make it to harvest. Your best weapon in those situations is information.

That’s our job. And this time around we want to talk about aphids on weed.

It’s a complicated discussion, not because aphids are impossible to get rid of. Plants can be treated, and in most cases, the pests can be eradicated.

What makes the story complicated is the fact that there are two types of aphids. Some attack cannabis plants’ leaves and others attack their roots.

Let’s talk about both.

Aphids on Weed Leaves

The infestation that’s easier to detect involves aphids that proliferate on the undersides of cannabis plant leaves and may also attack the stems. They’re sometimes known as blackflies or greenflies.

Don’t be fooled by their alternate names, though. These bugs are most often black or green, but they can also be yellow, red, brown, or even white. The green ones, for obvious reasons, are very good at hiding on the undersides of leaves.

Aphids are generally oval with soft bodies. Young ones (known as nymphs) are small and thin. Mature insects are rounder and develop wings as they grow, which is why they’re often mistaken for flies.

When you have winged aphids on your plants, your problems are magnified; they grow wings because the leaf is crowded with bugs — and they’re going to fly off and attack more of your plants. And aphids are born live, meaning plants quickly become infested. If the colonies are allowed to keep growing, they’ll eventually attack your buds as well.

These aphids cause two big problems for cannabis plants. The first is that they suck nutrients from the plants; as a result, leaves turn yellow or wilt and the plant’s growth is stunted. The second issue is that they release a sticky, sweet substance known as honeydew.

Honeydew brings additional headaches to a grow. It attracts a fungus called sooty mold, which accumulates and turns leaves black, makes the buds unhealthy to smoke, and attracts other insects, particularly ants.

These aphids usually don’t attack the roots of plants. Their relatives handle that work.

Root Aphids on Cannabis Plants

It’s obvious from their name where root aphids gather. They’re cousins of the aphids that attack cannabis leaves; all belong to the Phylloxera genus of insects which are notorious for plaguing all sorts of crops, from grapes and lettuce to basil and rice.

Root aphids, however, are particularly voracious when they attack weed plants.

These bugs look much like mealybugs, pear-shaped and white. Their appearance is similar to that of leaf aphids, but with shorter legs and antennae.

Root aphids gather and create enormous colonies at the bottom of cannabis plants, sucking nutrients from the root system and spreading a white, waxy web all around the roots. They release honeydew, which causes the same issues it does when their cousins release the substance on plant leaves. They can also sprout wings to travel to other plants and attack them, although some simply crawl to the next plant in line.

In addition to damaging and eventually destroying the roots of a plant, these infestations cause the plants to stop growing as leaves turn yellow and wilt from lack of nutrition. What’s worse, the yellow leaves can make growers think that their plants are simply suffering from nutritional deficiencies, since they can’t see any pests on the leaves.

A root aphid infestation is unfortunately much more difficult to treat than the aphids that attack cannabis leaves, but let’s take a look at the best approaches for both types of pests.

Getting Rid of Aphids on Cannabis Leaves

It’s possible, although somewhat rare, that an aphid infestation will just go away.

First, wasps love to lay eggs in the middle of aphid colonies. When wasps appear, aphids respond by creating a shell around themselves that prevents them from attacking the plant. Second, ladybugs are attracted to aphid infestations — and feed on the aphids they find.

However, that may not happen fast enough, or with enough scope, to save your plants. It can certainly help to purchase a large number of ladybugs (you can get them at many garden shops or online) and set them loose on your aphids.

That’s not all you should do, though.

Of course, regular inspection of your grow is crucial, not only to find signs of pests but to look for fungus and signs of nutritional deficiencies as well. And as soon as you see aphids gathering on the undersides of your weed plants’ leaves, it’s time to spray.

You can start by trying to “wash off” as many bugs as possible by hitting the plants with water from a power sprayer (bring indoor plants outside first, needless to say). If leaves have turned yellow and are badly infested, cut them off.

The next step is trying to weaken the bugs with an insecticidal soap or fatty acid salt spray. Horticultural oils like neem oil may also work, as long as you keep the spray far away from your flowers. If you have a tomato crop and have tomato leaf spray on hand, that’s another good approach. These sprays don’t last long on plants, so they’ll need to be reapplied regularly.

After that, or if the infestation is already out of control, you can try an organic pesticide that contains Spinosad. It kills aphids on contact but isn’t terribly harmful to other, beneficial insects. Two things to know about these pesticides: they have to be reapplied every 24 hours, and they’re not legal for commercial growers to use in many states.

Some growers use chemical insecticides to battle aphids, but the chemicals could get into your weed. Be careful.

Getting Rid of Root Aphids

Three words before we start: best of luck. Root aphids quickly get deep into the root structure of a cannabis plant, so some plants simply can’t be saved after an infestation has taken hold.

One thing you can try is purchasing nematodes (a fancy word for roundworms) and putting them into the soil. They’ll attack root aphids but won’t be very effective against a large colony. Some growers have had luck heating the soil with space heaters, or cooling it with water chillers; that may help destroy larvae, but extreme heat or cold can also damage the plant.

Sadly, the best bet is to use industrial-strength chemical insecticides which target aphids – but it could also hurt or kill beneficial bacteria and insects, and leave chemicals in your weed. Even those products may not work completely, because of the waxy protective web we mentioned earlier. Be sure that the insecticide you choose is safe for use on edible plants or those that produce food.

Sorry, but that’s all we’ve got. Root aphids are a very difficult problem for cannabis growers. They’re one more reason you should carefully inspect your plants daily, to catch any potential problems as soon as possible.

Aphids on Weed: FAQ

Q: How quickly does an aphid infestation progress?
A: Very, very quickly. In warm weather, newborns can mature and start reproducing in just a week. Aphids can give birth 10 times per day, and every aphid can produce as many as 60-80 nymphs per week. You don’t have to do the math to realize we’re talking about just a couple of weeks before plants may be overrun.

Q: Is there any way to protect a grow against aphids?
A: Not completely, but using best growing practices definitely helps. Change soil or rotate crops with every grow, sterilize tools and containers regularly, avoid cross-contamination, and isolate clones for several weeks before introducing them into the grow. You can’t inoculate your plants against aphids, so the best bet is to do everything possible to prevent that first bug from making it into your grow room.


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  • Durak, R., Jedryczka, M., Czajka, B., Dampc, J., Wielgusz, K., & Borowiak-Sobkowiak, B. (2021). Mild abiotic stress affects development and stimulates hormesis of hemp aphid Phorodon cannabis. Insects, 12(5), 420. [2]