Whiteflies

Whiteflies are small sap sucking insects that look like tiny white moths. They feed on the underside of leaves, weaken the plant slowly, and coat everything below them in sticky honeydew.

What you are seeing#

Shake a branch. If a small cloud of white specks lifts off, circles for a second and settles back under the leaves, you have whiteflies. Nothing else in a tent behaves like that. Adults are about a sixteenth of an inch, bright white, with wings tented over the body and a faint powdery coating.

Turn the leaves over, especially in the lower and middle canopy. At 30x you will find the rest of the life cycle stuck to the underside: oval yellowish eggs laid in loose arcs, and flat translucent scale-like nymphs that do not move at all. Beginners miss the nymphs entirely because they look like part of the leaf.

Below the colonies, leaves go shiny and tacky with honeydew, then grow a black sooty film on top of it. Fed-on leaves turn pale and mottled, then yellow, and drop from the bottom up. Yellow sticky cards at canopy height fill quickly and are the easiest way to track the population.

Why it happens#

They come in on nursery clones, on a houseplant moved into the room, or through an open window or unscreened intake from an outdoor garden.

They stick around because of the nymph stage. Once a nymph settles it is immobile, flat, and largely shielded from contact sprays, so a treatment that knocks down every adult in the tent still leaves a full replacement generation glued to the leaves.

Warm still air, a crowded canopy and soft nitrogen-heavy growth all speed them up.

How to fix it#

1. Hang yellow sticky cards at canopy height today. They are strongly attracted to yellow, and the cards are both a control and your population count.
2. Vacuum the adults. A handheld vacuum run slowly under the leaves in the morning, when they are sluggish, removes a large share of the breeding adults in a few minutes.
3. Remove the worst-infested lower leaves, bag them, carry them out.
4. Spray leaf undersides with insecticidal soap, lights off, to the point of dripping. Coverage of the underside is the entire job; a nymph you did not wet survives.
5. Repeat every 4 to 5 days for at least 3 weeks. Eggs hatch in 5 to 10 days and soap does not affect them, so a single spray clears the adults and hands the tent back to the next generation a week later.
6. Rotate products between rounds, for example soap one week and horticultural oil at 0.5 to 1 percent the next, in vegetative plants only.
7. Get air moving, screen the intake, and quarantine new plants for 2 weeks going forward. Whiteflies are weak fliers and dislike a breezy canopy.

How to tell it apart#

Versus aphids. Both produce honeydew and sticky leaves. Whiteflies fly up in a cloud when disturbed and their adults are white and winged. Aphids cluster on stems and new growth in visible clumps, are green, black or pink, and stay put when touched. Shaking the plant settles this in one second.

Versus fungus gnats. Gnats are dark, not white, hover near the soil surface rather than the leaves, and leave no stickiness anywhere. If the bugs are on the medium, they are gnats.

Versus thrips. Thrips leave dry silvery scarred patches with black frass specks and no stickiness. Whitefly damage is pale mottling with a tacky surface. Feel the leaf: sticky means whiteflies or aphids, dry and scarred means thrips.

How long until it looks better#

Adult counts drop within 2 to 3 days of vacuuming and hanging cards. Expect the population under control at 10 to 14 days and genuinely cleared at 3 weeks if you hold the spray schedule.

Yellowed and mottled leaves do not recover and should be removed once the plant is stable. Sooty mold wipes off with a damp cloth but the leaf underneath may already be spent. Judge recovery on new growth staying clean and on sticky cards catching nothing for two weeks running.