Root aphids, other pests, and how to avoid them

One of the biggest challenges facing cannabis cultivators is how to avoid pests, such as root aphids, spider mites, and fungus gnats. Left untreated, these infestations can cause serious damage to your crops. Root aphids are notorious for infesting cannabis, as well as the succulent family of plants and numerous trees.

Here you'll learn how to get rid of root aphids and other pests that threaten the health of cannabis plants.

What are root aphids?

Resembling mealybugs, root aphids are invasive white growths that attack the root systems of cannabis plants. Alternately referred to as white soil mites, root aphids are not only a problem for cannabis plants but also for asters, hosta, rice crops, fir trees, and herbs such as basil and oregano.

However, root aphids can be particularly malicious toward cannabis plants. Seasoned cannabis cultivator Steven Somoza of Hydroponics, Inc., depicted them as a "sneaky and infamous pest for cannabis growers. They propagate in staggering numbers at the root zone, destroying the root as they leech nutrients."

Indeed, root aphids can be ruthless in their quest to feed off of cannabis plants.

What do root aphids do?

Root aphids act like vampires in the soil, depleting entire root systems by sucking out vital moisture. When under attack, plants will experience stunted growth, wilting, and yellowing leaves. The damage that these pests inflict is often mistaken for nutrient deficiencies, which may display similar symptoms. But there are several ways you can distinguish between a pest problem and a nutrient deficiency.

wilting cannabis plants
When under attack by root aphids, cannabis plants will experience stunted growth, wilting, and yellowing leaves.
Photo by: Gina Coleman/Weedmaps

How do you know if you have root aphids?

You can identify root aphids by their teardrop shape and a pair of pointy protrusions on their hind ends. These aggressive pests, which belong to the Phylloxera family of insects, grow in clusters and cover plant roots with soft, tissue-like masses. You may also observe ants congregating near your plants, as they are attracted to the honeydew that root aphids excrete.

How to get rid of root aphids

A widespread infestation on a plant root system may be difficult or impossible to treat. Fortunately, there are several courses of action you can take against root aphid predators if you catch them early enough.

Treating root aphids with insecticides

While not foolproof, insecticides can be moderately effective in killing root aphids which have a natural wax coating that protects them against such chemicals. Be aware, though, that any insecticide you use can be toxic to beneficial insects such as bees and butterflies, not to mention harmful to humans and pets.

But if you're willing to take a risk that the treatment might fail or harm other species, here's how to treat root aphids with insecticides:

Drench your growing medium, soaking it through with an industrial-strength insecticide. This method will be most effective with dense soil as opposed to poorly draining soil that contains high amounts of peat moss and bark. However, any soil drench will travel quickly into the plant's body, meaning that the roots may not receive enough of the pesticide for it to work. To maximize the insecticide's potency, repeat the soil drench two weeks after completing the initial one.

cannabis seed in soil
To treat root aphids with insecticides, drench your growing medium, soaking it through with an industrial-strength insecticide.
Photo by: Gina Coleman/Weedmaps

Growers have had varying levels of success with the following pesticides:

  • Dinotefuran
  • Imidacloprid
  • Cyfluthrin
  • Malathion
  • Thiamethoxam

These pesticides contain bases of natural ingredients derived from essential oils, especially rosemary and lemongrass. Using these essential oils in their raw form may serve as a spot treatment on root aphids but are unlikely to fully eradicate the issue.

Treating root aphids with nematodes

You can also try introducing nematodes (roundworms) into the soil. As Somoza shared, "We have farmers who have seen great success with helper or 'predatory' nematodes which are harmless to humans and to plants."

Nematodes are also harmless to earthworms, which are an important component of any natural soil. At the first sign of infestation, apply a treatment of nematodes to moist soil as these parasites will attack root aphids and other soil-borne pests. Parasitic wasps and ladybugs are also notable for their potential to attack and kill aphid eggs.

In terms of what doesn't work to kill root aphids, setting traps is not usually a good solution. Because the problem originates underground, deep in the root system, sticky traps are superficial and do not address the core concern. However, some indoor cannabis growers have reported success with yellow sticky traps as the bright color draws the aphids.

Further, the aphid life cycle can be problematic, as these insects reproduce quickly and lay eggs in large numbers (up to 150 in a span of 45 days) that are difficult for growers to manage. If all else fails, there is one other treatment you can try: temperature control.

What temperature kills root aphids?

There may not be one particular temperature that kills root aphids, as cultivators have experimented with both heat and cold to favorable results.

Somoza explained, "We've had reports of outdoor growers using heaters at the root area to deter aphids and destroy the larvae. Another farmer found success indoors using water chillers and high doses of H2O2." (H2O2 is hydrogen peroxide.)

Therefore, application of extreme heat or extreme cold may be effective in killing aphids. Exercise caution, though, as cannabis plants thrive in a moderate temperature range of 65 to 80 degrees Fahrenheit during most stages of growth.

How to prevent root aphids and other pests

Since even the strongest pesticide may not banish root aphids, the best way to prevent infestations in the first place is to keep garden equipment clean and rotate crops regularly. Sterilize reusable containers and avoid cross-contamination from plants. Vigilance in all aspects of cultivation can deter many types of harmful pests from destroying your harvest.

Somoza elaborated, "An infestation can be overwhelming...the best practices to avoid pests are cleanliness and a solid integrated pest management schedule that utilizes safe products for you and your garden."

In the end, good gardening hygiene is the most useful strategy to keep your grow area free of root aphids and other pests, including fungus gnats and spider mites.

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The information contained in this site is provided for informational purposes only, and should not be construed as medical or legal advice. This page was last updated on September 8, 2020.