Aphids on Cannabis: Signs and Treatments

You have found clusters of small soft-bodied bugs on your stems, and the leaves feel sticky. Those are aphids. They are big enough to deal with directly, and easing off nitrogen helps keep them away.

Cannie showing advanced aphids — Advanced

“Little sticky squatters on my stems! Aphids, time to pack up.”

Where it shows

Stems and leaf undersides, in visible clusters.

What it looks like

Clusters of small soft-bodied insects on the stems, leaves curling, foliage glazed sticky with honeydew and later blackening with sooty mold.

How to confirm it

Check stems and leaf undersides for clusters of insects.
Leaves curl as they feed.
Foliage feels sticky from honeydew.
Sooty black mold grows on the honeydew later.
Ants may be farming them.

Why it happens

Often follows over-feeding with nitrogen. Soft sappy growth full of free amino acids is exactly what sap-feeding insects are looking for.

Overfeeding nitrogen, which makes soft, sappy growth they love.
Infested clones or plants brought in.
Ants protecting and spreading them.
Outdoor plants exposed to aphid flights.

How to fix it

Cannie's quick fix, in order:

Ease off the nitrogen. Lush over-fed growth is what attracted them.
They are large enough to remove physically: in veg, a strong water spray knocks most off. Never spray water into buds in flower.
The sticky honeydew grows sooty mold, so clean the leaves after treating.

Ease off nitrogen. Lush, overfed growth attracts them.
In veg, knock most off with a strong water spray.
Wipe or prune heavy clusters by hand.
Clean leaves after treating, since honeydew grows sooty mold.
Repeat checks every few days.

Organic options

Ladybugs

Eat aphids in large numbers. Release at dusk and keep lights off briefly so they settle. Safe in flower.

Lacewings

Larvae hunt aphids. A good option in flower when sprays are off the table.

Insecticidal soap

Kills aphids on contact. Use in veg only, with gloves and eye protection, and follow the label.

Neem or karanja oil

Use in veg only, never on buds. Never combine with sulfur.

Read and follow every product label. Organic friendly does not mean certified organic; check the listing if that matters to you.

Veg or flower?

In veg, water sprays and soaps work well. In flower, never spray buds; use beneficial insects and hand removal instead.

Prevent it next time

Do not overfeed nitrogen.
Quarantine new plants.
Control ants near outdoor plants.
Inspect stems and leaf undersides every few days, and daily once you have seen one.

Questions growers ask

Why do aphids appear on my cannabis?

They are drawn to soft, sappy growth from too much nitrogen. Infested clones and ants also bring them in.

Are ladybugs safe to use in flower?

Yes. Ladybugs and lacewings are good flower options since they leave no spray residue on buds.

What is the sticky stuff on my leaves?

That is honeydew from aphids. It grows black sooty mold if left, so clean it off after treating.

Where these figures come from

These points match published grow books, page by page. They are grower practice, not research: none of these books cites a study, so where science and the books differ, this page follows the science.

Insecticidal soap, veg only. Danko (2018), e-book p. 128. Green (2001), p. 320.
Ants may be farming them. Green (2001), p. 322 to 323.

Books: Danko, Cannabis: A Beginner's Guide to Growing Marijuana (Hampton Roads, 2018); Green, The Cannabis Grow Bible (4th ed., 2001); Paull and Zetta, Foolproof Guide to Growing Cannabis (2020) and The Cannabis Grow Bible (2020).