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.
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