Aphids

Aphids are soft bodied sap suckers that gather in visible clusters on stems and new growth. They are the easiest pest on this site to identify with the naked eye and, caught early, one of the easiest to clear.

What you are seeing#

Clusters. Dozens of pear-shaped bugs about an eighth of an inch long packed together on a stem, a petiole, or the underside of a new leaf. Color varies by species: green, black, pink, gray or nearly translucent. They barely move when you touch them, which is a useful tell.

Check leaf undersides and the soft new growth at the tops. Aphids want tender tissue, so they concentrate on growing tips, not old fan leaves. At 30x you will see two small tubes, called cornicles, sticking out the back end like exhaust pipes. Nothing else on a cannabis plant has those.

Then look for what they leave behind. Leaves below a colony go shiny and tacky with honeydew, their sugary waste, and within a week or two black sooty mold grows on it. You may also find pale shed skins that look like white flecks and get mistaken for a second pest.

Heavily fed new growth comes in curled, twisted and undersized, and older leaves yellow and drop.

Why it happens#

They arrive on clones, on soil, through an open window, or on you. Winged forms appear when a colony gets crowded and fly to the next plant.

They multiply faster than beginners expect. Indoors, females give birth to live young without mating, and a single aphid can produce offspring within a week of being born. That is why a colony you glanced at last Tuesday is three times the size on Sunday.

Soft, heavily nitrogen-fed growth attracts them, as does a still tent and a dense canopy nobody looks inside.

How to fix it#

1. Wipe the colonies you can reach today. With a population this visible, mechanical removal gets you most of the way. Wear a glove and run your fingers down the stem.
2. Knock the rest off with water. A firm spray on the undersides dislodges them, and aphids are poor at climbing back onto a plant.
3. Remove the worst growing tips entirely and bag them before carrying them out.
4. Spray insecticidal soap on undersides and stems, lights off, to run-off. Soap kills soft bodied insects by contact and aphids are about as soft as it gets.
5. Repeat every 4 to 5 days for 3 rounds, about 2 weeks. Soap kills only what it wets, so nymphs deep in the colony or born after you sprayed are untouched. One application always leaves survivors and the population rebuilds in a week.
6. Check for ants. Outdoors and in garages, ants farm aphids for honeydew and actively protect them. Deal with the ant trail or you will not win.
7. Wipe the honeydew off with a damp cloth so sooty mold does not establish.
8. Over the next week, dial nitrogen back to label strength if you have been pushing it, and get a fan moving through the canopy.

How to tell it apart#

Versus whiteflies. Both leave sticky honeydew, and this is the pairing people mix up. Whiteflies fly: shake the plant and a cloud of tiny white moths lifts off and resettles within seconds. Aphids sit still in clumps. Aphid colonies are on stems and tips, whitefly adults are flat under leaves.

Versus spider mites. Mites are much smaller, need a loupe to see at all, do not cluster on stems, leave fine pale stippling, and produce webbing. Aphids are visible without magnification and leave stickiness instead of stippling.

Versus thrips. Thrips are narrow and fast and leave dry silvery scarring with black frass specks. If the leaf feels sticky, you are looking at aphids or whiteflies, not thrips.

How long until it looks better#

Mechanical removal plus the first soap spray usually takes out most of the population in a day. Expect the colony to be gone within 10 to 14 days on the full 3 round schedule.

Curled and twisted leaves stay curled. That tissue formed wrong and will not straighten out. Judge recovery on the next set of growing tips, which should come in flat and normal sized within 7 to 10 days.

Keep checking the tips weekly for a month. Aphids are easy to beat and easy to reintroduce, and the second round always starts in the same place: the newest, softest growth on the plant.