Quick answer: Root aphids are small, soft-bodied aphids that feed on cannabis roots below the soil line. A heavy infestation leaves plants wilting, yellowing and growing slowly. To confirm them, slide the plant out of its pot and check the root ball with a hand lens. Winged aphids stuck to the upper sides of leaves are another clue.

What Are Root Aphids?

Root aphids are aphids that live and feed on roots instead of leaves and stems, so most of the colony stays hidden below the soil line.

The rice root aphid is a dark olive-green aphid with a rounded body. Colorado State University researchers name it the most common aphid reported from indoor marijuana production in Colorado.

Other root aphids, such as the sugarbeet root aphid (Pemphigus betae), are covered in white wax and can be mistaken for mealybugs, though they’re smaller. UMass Extension notes that root aphids have reduced cornicles that look like rings at the end of the abdomen and can be seen under magnification.

Rice Root Aphid Life Cycle

Rice root aphids reproduce without mating, and females give birth to live daughters. They mature in about 9 to 10 days and adults live for about a month. At 73°F, a population can double every 1.6 days. Most stay wingless on the roots, but winged adults form from time to time, climb out through cracks in the soil and fly to new plants.

Signs of Root Aphids on Cannabis

Root aphids feed out of sight, so the first clues show up above the soil. Root feeding causes reduced vigor, slow growth, wilting and leaf yellowing, and heavily infested plants can be stunted. Colorado State University reports that cannabis plants carrying large rice root aphid populations can show a significant decline.

• Wilting or drooping leaves
• Yellowing leaves
• Slow, stunted growth
• Winged aphids caught on the upper surfaces of leaves, where leaf hairs trap them
• Dark aphids in the soil at the base of the stem
• Aphid clusters or white, waxy residue on the roots

Wilting and yellowing also come from overwatering, root rot and feeding problems, so the next step is a quick look at the roots.

How to Check Cannabis Roots for Aphids

1. Pick a plant that shows symptoms and gently slide it out of its pot.
2. Look for clusters of small aphids or white, waxy residue on the outside of the root ball, where roots press against the pot wall.
3. Use a hand lens to confirm what you see. Under magnification, root aphids show reduced, ring-like cornicles at the end of the abdomen.
4. Check the soil surface at the base of the stem and the upper sides of leaves for dark, winged aphids.
5. Hang yellow sticky traps near the plants to catch winged aphids moving between pots.

Root Aphids vs. Fungus Gnats and Root Mealybugs

Three soil pests turn up around cannabis roots, and each needs a different response.

Pest	What you see	Where to look	What helps
Root aphids	Small, soft aphids; dark olive-green, or covered in white wax	On roots and in the soil; winged adults on the upper sides of leaves	Removing infested plants, a host-free week, soil-dwelling predatory mites
Fungus gnats	Small, dark, delicate flies with long legs and antennae; larvae are whitish with a shiny black head	Adults on soil, leaves and nearby surfaces; larvae in damp potting mix	Letting the top of the mix dry between waterings, yellow sticky traps, Steinernema feltiae nematodes or Hypoaspis predatory mites
Root mealybugs	Masses of fine, powdery white wax on the roots	In crevices of the mix and on the outer edge of the root ball	Discarding infested plants and debris, cleaning pots before reuse

Sources for the table: Colorado State University for root aphids, the UC Statewide IPM Program for fungus gnats and UMass Extension for root mealybugs.

Winged root aphids and adult fungus gnats can both end up on sticky traps. Fungus gnats are slender, mosquito-like flies, while winged root aphids keep the rounder aphid body. For more on gnats, see beneficial nematodes for cannabis growers and the fungus gnat and mealybug sections in protecting marijuana plants from pests and bugs.

How to Get Rid of Root Aphids on Cannabis

Root aphids live and feed in the root zone, out of sight. Colorado State University’s guidance centers on removing infested plants, breaking the life cycle with a host-free period and using soil-dwelling predators.

Isolate and Remove Infested Plants

Move plants with confirmed root aphids away from healthy ones. Discard heavily infested plants along with their used potting mix, and clean pots before reusing them.

Give the Grow Space a Host-Free Week

Colorado State University notes that rice root aphids can be wiped out with a brief host-free period. They live only a few days without a living host plant, and indoors they don’t leave a lasting egg stage. That means about one week with no plants in the space should let them die out.

Add Soil-Dwelling Predators

Many aphid predators, such as lady beetles, green lacewings and most parasitic wasps, aren’t suited to aphids that live on roots. Colorado State University says soil-dwelling generalist predators such as Stratiolaelaps scimitus (formerly Hypoaspis miles) are likely to be most effective in soil. For hydroponic root zones, it says no commercially available predators are likely to be adapted. Our overview of beneficial insects for cannabis growers covers these soil mites.

Track Winged Aphids With Sticky Traps

Yellow sticky traps show whether winged aphids are still moving around the grow. Check them throughout the year.

How to Prevent Root Aphids

How Root Aphids Get Into a Grow

Colorado State University points to infested plants as the likely way most indoor grows pick up rice root aphids. Winged aphids can also come in through vents, and plants taken outdoors can pick them up and bring them back inside. Once inside, root aphids can move between pots through drainage holes and in irrigation water that drains from one pot to another.

Growing style plays a part too. Surface mulches, often used in continuous indoor live-soil growing, have been shown to favor rice root aphids. The same aphid also lives on the roots of grasses such as wheat and barley.

Prevention Habits That Work

• Inspect new plants, including the root ball, before they join the main grow, since infested plants are the likely way in.
• Keep each pot draining on its own, so runoff doesn’t flow from one pot into the next.
• Keep indoor plants indoors, and watch yellow sticky traps near vents and other openings.
• Avoid excess nitrogen, and manage grasses and sedges in and around growing areas.
• Keep yellow sticky traps up all year to catch winged aphids early.

Frequently Asked Questions

What Do Root Aphids Look Like on Cannabis?

The rice root aphid is a small, dark olive-green insect with a rounded body. Colorado State University names it the most common aphid reported from indoor marijuana production in Colorado. Other root aphids are covered in white wax. Most stay on the roots, but winged adults sometimes turn up on the upper sides of leaves.

Do Root Aphids Fly?

Some do. Most rice root aphids are wingless and live on the roots, but winged adults form from time to time, climb out through cracks in the soil and fly to new plants. Yellow sticky traps hung near the plants are a simple way to catch them.

Where Do Root Aphids Come From?

In indoor grows, they most often arrive on infested plants. Winged aphids can also enter through vents and other openings or colonize plants that spend time outdoors. Rice root aphids also live on the roots of grasses such as wheat and barley.

How Serious Are Root Aphids on Cannabis?

They can be serious once populations build up. Colorado State University reports that cannabis plants carrying large rice root aphid populations can show a significant decline. Colorado State University also notes that root feeding may leave small wounds that make it easier for root rot to take hold. Utah State University lists reduced vigor, wilting and yellowing among the signs.

Do Beneficial Nematodes Kill Root Aphids?

The UC Statewide IPM Program lists beneficial nematodes such as Steinernema feltiae as a control for fungus gnat larvae. For root aphids, Colorado State University points instead to soil-dwelling predatory mites such as Stratiolaelaps scimitus (formerly Hypoaspis miles) as the natural enemies likely to be most effective in soil.

How Do You Get Rid of Root Aphids Between Grows?

Remove the plants and leave the space without any living plants for about a week. Rice root aphids live only a few days without a host and don’t leave a lasting egg stage indoors, so a host-free week should let them die out. Clean the pots and start again with fresh mix.

Sources

• Colorado State University, Hemp Insects: Rice Root Aphid
• Colorado State University, Hemp Insects: Rice Root Aphid (with photos)
• Cranshaw et al., Colorado State University, Developing Insect Pest Management Systems for Hemp in the United States (Journal of Integrated Pest Management, 2019)
• Utah State University Extension, Rice Root Aphid
• Michigan State University Extension, Root aphids: the underground pest on succulent plants
• UMass Extension, Aphids on Greenhouse Crops
• UMass Extension, Mealybugs in Greenhouses
• UC Statewide IPM Program, Pest Notes: Fungus Gnats