Root aphids

How can I eliminate or at least vastly inhibit aphid colonization? They are colonizing at roots on rockwool cubes exposed to the atmosphere.
Guerneville, California

Root aphids colonize and suck juices from roots in many mediums including horticultural pebbles, rockwool and planting mixes. They are persistent, so it requires some discipline to eliminate them. There are several organic products that can be used without affecting the plant, the buds, or the safety of the buds for later human consumption. The first is organic pyrethrum. This is a natural insecticide gathered from a chrysanthemum-type flower. There are several brands of liquid concentrate. If pyrethrum liquid is not available at your local nursery or garden shop you can order it on the internet.

Botanigard is an insecticide that is composed of a living fungus, beauveria bassiana. This fungus seeks out aphids and infects them, causing death. Then it releases spores waiting for more victims. It also works to control whiteflies and thrips. You can order it at many garden stores or through garden websites on the internet.

Neem oil and citrus oil have also been used to kill aphids, but they sometimes affect the roots. Test them on a sample plant before using either of them in the garden.

The aphids should be treated every other day with a minimum of six treatments. Rotate the insecticides. Botanigard can be combined with pyrethrum. The neem and citrus oils can be mixed with each other as well as pyrethrum. The idea is to totally eliminate the pests.

If the plants are growing in a hydroponic system, rather than mixing the treatment in the reservoir, make a special batch of water. Turn off the hydroponic system and water the plants using a watering can. Let the insecticide water stay in the root area for at least an hour before turning the hydroponic unit back on.

Once the aphids are gone, it is difficult for them to reinfect. They were probably introduced to your garden by a new element such as a clone or infected planting mix.

Readers with grow questions (or answers) should send them to Ed at: Ask Ed, PMB 147, 530 Divisadero St, San Francisco, CA 94117, USA.
You can also email Ed at [email protected] and send queries via his website at
All featured questions will be rewarded with a copy of Ed’s book, The Big Book of Buds. Sorry, Ed cannot send personal replies to your questions.



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  16. Anonymous on

    I used baer tree and shrub. only on the vegging plants. i just followed the directions on the bottle. it completely wiped them out. its been almost 1 month, and not a one of those evil creatures have been found. groth is back to normal,and I see nothing but brite white roots, where as before, they ate the roots to the point that they were brown, with major root rot.

  17. DanTheHydroMan on

    Hi I red a few of your articles about root aphids and I have been battling them for a while. I have watered with nematodes twice in a row now I am starting to see the aphids walking around on the floor but they are still in the root zone ( soiless mix) so I did a pyrethrum bomb to take care of the exposed live aphids and I ordered botanigard so now I’m going to water with that today bomb in two days then add more nematodes and bomb in two more days if seeing aphids on the ground still do u think that should take care of them or do I need to water with the pyrethrum also?if so what brand do u recommend? I looked for some and a liter ranged from $11 to like $175 so I’m not sure what kind to get.

  18. Anonymous on

    We were very pleased to find the article on root aphids. We basically had the identical scenario as the grower above with what seemed to be a severe infestation of hundreds or perhaps thousands of aphids attached to and crawling on the roots in the netpots. This was really freaky and scary!

    Twice now, a pest infestation was the gift of receiving contaminated clones from another source. I have learned my lesson about receiving clones from another party, even if that party has a good reputation and supposedly is an expert in the field plant cultivation. If I ever need clones again, each plant will get dipped in Neem, Pyrethrum, or Azamax before being introduced into my system. My first infestation from 3rd party clones was spider mites and now most recently root aphids.

    Unfortunately by the time I realized what we had, there was no time to order products like Botanigard, or liquid concentrated pyrethrum over the internet. We needed to something fast or risk loosing everything. Non of the three hydro shops nor any of the nursery supply establishments in my area, carried these products. What I was able to find that effectively did the job in two applications, was a combination of ‘Azamax’ (azadirachtin) and Green Light ‘Rose Defense’ (clarified hydrophobic extract of neem oil). Both products are suitable for organic growing.

    Azamax is not cheap and in order to save on insecticide and at the same time directly target the infected area, I decided to deviate from the instructions and use my own method of application.

    My hydro setup is a General Hydroponics Aeroflow 20 system.

    1.) First of all, assuming that aphids don’t have gills, I raised the level of water in the tubes to the highest possible level with the hopes of drowning as many of the little bastards as possible.

    2.) In a standard one gallon garden sprayer I added 1.5 Tbs of Azamaz (.6%) and 4 caps full of Rose Defense.

    3.) Then I individually lifted each netpot out of the Aeroflow 20 tube as far as possible without tearing the roots and using the garden sprayer, first saturated the top surface of the pot so that the insecticide penetrated deep into the surface of the rockwool substrate and into the roots. Then gently rotating the netpot from side to side, I also saturated the rockwool from the outside. Fortunately I didn’t use coco baskets this round, which made the treatment more effective. Of course all of the insecticide eventually soaked through the netpots and began circulating through the hydroponic system. Almost immediately, dead and slow moving aphids were flushing into the reservoirs. When the treatment was complete, I allowed the water to circulate for two hours before draining the system and adding fresh water, nutrient and Botanicare ‘Aqua Shield’.

    Note: The aphids (and associated particles) flushing into the reservoir were so small that the cylindrical filters of the pump intakes were not fine enough to keep them from entering and clogging the laser tubes. I replaced the course spunge-type filters with one gallon paint strainer bags which are available at any retailer that sells house painting supplies. These worked so well, that this is all I use now. They do however need to be tied on with twine, which is not a big deal.

    4.) After one week I examined all of the net pots and could find only one live aphid slowly crawling around. If I found one, it was highly likely that there were more. Following the same process as above, I repeated the treatment. The only deviation from my first treatment was that I decided to lower the water level in the tubes to 50% as not to immediately flush the insecticide out of the roots in the netpots.

    The plants are now regaining their normal color of dark green, are growing well and otherwise seem healthy.

    I hope this additional information helps anyone that might run into this problem.

  19. on war path on

    hey I have liquid pyrethrum at 5% and i want to flood the root arae to kill root aphids but i am not sure how much pyrethrum to add per gallon so i don’t kill my plants.