Alocasia attract spider mites more reliably than almost any other common houseplant. Thin leaves and the warm, dry indoor air these plants are usually kept in are close to ideal breeding conditions.
The velvet-leaved species are worst of all. Alocasia micholitziana 'Frydek', Alocasia reginula and the jewel types hide early webbing in their leaf texture, so the infestation is often advanced before anyone notices.
Spot them early
Mites are barely visible, under half a millimetre. Look for the signs instead.
- Fine pale speckling across the leaf surface, as if it has been dusted
- Delicate webbing where the petiole meets the leaf, most visible in raking light
- Dull, faded leaves that have lost their gloss
Check the undersides weekly. Wiping a white tissue across the underside and finding rust-coloured smears confirms it.
Treatment
- Isolate the plant immediately. Mites move between touching plants within days.
- Shower the plant. Lukewarm water, firm pressure, undersides especially. This physically removes the bulk of the population.
- Treat with insecticidal soap or neem. Coat every surface, undersides included. Do this out of direct sun to avoid leaf burn.
- Repeat every 5-7 days for at least three rounds. Neem and soap kill adults and nymphs but not eggs, so the repeats catch each new hatch.
- Raise the humidity. Mites struggle above 60% humidity, which is where Alocasia want to be anyway. This is prevention as much as treatment.
Stopping after one treatment because the plant looks better is why infestations return a fortnight later.
A note on velvet leaves
Do not shower or wipe the velvet-leaved species with water, because it marks the surface permanently. Use a soft dry brush to dislodge what you can, then treat with a fine spray held well back from the leaf.
Other pests to watch for
Thrips
Silvery streaking and deformed new leaves. Harder to shift than mites, so expect a longer treatment cycle.
Mealybugs
White cottony clusters in the leaf joints. Dab each one with a cotton bud dipped in rubbing alcohol, then treat as above.
Fungus gnats
Small flies around the soil. Harmless to a healthy Alocasia, but a signal you are watering too often, which for this genus is the more serious problem.
Prevention
Quarantine every new plant for two weeks. Keep humidity up. Inspect leaf undersides when you water.
Mites caught in week one take one treatment cycle. Mites caught in week four can take a month and cost most of the foliage.
