Root Aphids and the Cannabis (Marijuana) Plant

by Alex Robles

If you’ve never had root aphids before, count yourself lucky.  They are sinister little bastard that can be easily misdiagnosed.  Since “knowing is half the battle”, I want to share everything I’ve learned about them.

What are they:

The Root Aphid is in the Phylloxera family of insects, more specifically it is from the Pemphigus species and feeds on a lot of different plant roots.

– Their bodies are about 1mm long and are more pear-shaped (mealybugs are more oval shaped).  They will also have small cornicals or “tail pipes” at the end of their abdomen like most aphids (mealybugs don’t).  They’re also about the same size or a little smaller than stem-and-leaf aphids.

-The root aphids will have rings on the lower part of the body, towards the ass. You can see the rings when you look at them under magnification.

-Their color is going to range from brownish-orange, yellowish- green, pinkish-white and brown.

-People also misidentify them as mealybugs because they’re also covered in this white waxy cast (molted) skin that they leave behind.

-The root aphid will reproduce asexually during the spring and summer, which means unmated adult female aphids will  give birth to live young, all of which are female.

-They can give birth to 60-100 nymphs in their 30 day lifespan.  Those nymphs are going to mature pretty fast, in about 7-10 days if conditions are right and left unchecked.

-When the plant is almost dead and out of nutrients or when the population is really high ( like during and infestation) winged females start to develop.  They are going to fly off and infest new less crowded plants.

(In their winged stage, they can be confused with fungus gnats.  The gnats are skinnier and more mosquito looking.)

-In the fall, the root aphid will sense when winter is coming and male winged aphids will start to develop and mate with the females.

-The will lay the eggs that will overwinter in the soil or attached to leaves and stems above the soil.  When the temperature warms up they’ll hatch and cycle of infestation continues.


The root aphid will bore into the root and suck out the the plants life juice (sap).  As they feed they make scars and leave the plant root exposed, this makes it easy for mildew and disease to infect the roots.  Plant roots will turn yellow, swell, and then harden in the spots where the root aphids feed on them

– Aphids also poop out a sugary liquid called honeydew which helps a black fungus grow known as sooty mold and it attracts ants.

– The first sign of root aphids is going to be your plant slowing down and not growing as vigorously as it was.  It’s going to start to look withered, curled, and the leaves will start to yellow. It’s sometime misdiagnosed as a magnesium or iron deficiency.  .

How to control them:

Do not take a ‘WAIT AND SEE” attitude when you first discover root aphids.  It will not take them long to take hold and when that happens they will put up a fight.

  • Use yellow sticky cards to trap any flyers that could make their way into your grow area.  They aren’t very effective against the crawlers.
  • Don’t over water your plants, overly wet soil is attractive to root aphids.
  • Some soil mixes and compost that’s still to raw could come with root aphids.
  • Keep your grow area clean, don’t leave discarded plant material laying around.  That could give them more places to live and thrive.
  • Isolate any new plant and thoroughly inspect them before you put them in your grow area.
  • It’s important to rotate insecticides with different modes of action so the aphids don’t develop a resistance to them.
  • If your removing an infected plant, be careful not to drop soil or spread aphids into other parts of your garden.

How to fight them:

Green lacewing: Chrysoperla rufilabris adults are usually active at night and feed on nectar, pollen, and honeydew. The lacewing larvae (referred to as ‘aphid lions’) feed on a lot of different aphid species as well as mites and whiteflies.

Predatory midge: Aphidoletes aphidimyza feeds on over 60 aphid species. The midge is nocturnal and likes the dark, humid areas near the lower plant canopy. The bright orange larval will kill the aphids by biting their knee joints and injecting a paralyzing toxin.  After that they’ll suck out the body fluids.

Ladybugs:  Will eat the aphids that are on the plant and the surface of the soil but they’re not going to do much for the buggers underground.

Beneficial Nematodes:  Will help kill those soil dwelling pest but are harmless to earthworms, pets and humans.

Neem Oil:  Can help stop aphid infestations from growing because it strips the outer protective wax layer off the exoskeleton.  It doesn’t help with the eggs so you reapply 7-10 days.

  • Make sure the soil is completely dry.  Simply mix two tablespoons per gallon of water and soak the roots of your plants.

Clean Playground Sand:  You can buy this at any hardware or home improvement store.  Sand is like glass and stops them from going into your roots. Place about 1-2 inches on the top and bottom of your grow pots.  Subcool mentioned he does this for gnats.

Hydrogen Peroxide:  Works by killing the aphid larvae.  Be careful when using it because it can harm the roots if you use too much.

  • Dry out the soil for a couple of days, then mix 1 part hydrogen peroxide to 4 parts water and soak your infected cannabis plants. When the growing medium starts to foam, it means the larvae a now being killed.

Pyrethrum sprays: These foliar  sprays can be effective when used early  in the infestation. When you water lightly after applying, it will disperse this chrysanthemum-based botanical into the soil. Reapply every two weeks (eggs in soil may continue hatching) until plants regain vigor and all aphid sign disappears.

I hope this information helps your fight  against the dreaded “Root Aphid”.

Click here to listen to the “In My Grow Show” podcast.


Grow Learn Teach

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