Alocasia Polly Spider Mites: Confirm, Wash, Treat, Recheck

Pale speckles on a Polly leaf are alarming, especially on a plant that only carries a few leaves at a time. Spider mites are a known risk here. Missouri Botanical Garden’s entry for Alocasia × amazonica ‘Polly’ lists one problem: watch for spider mites. NC State Extension says the whole Alocasia genus is prone to them, and advises monitoring for them on Alocasia × mortfontanensis, the name NC State now uses for the plant sold as A. × amazonica.

The same steps work for any Alocasia. Confirm the pest first, then treat the undersides, where the mites live.

Confirm it is spider mites

Mites are hard to see. UC IPM’s spider mite pest note says you will usually notice the damage before the mites. Check for these signs together:

• Stippling. Fine light dots on the upper leaf surface where mites have sucked out cell contents. On Polly’s dark green blade they show up as a dull, sandy speckle.
• Bronzing or yellowing. UC IPM notes that heavily fed leaves can turn bronze, then yellow, and drop.
• Mites and eggs underneath. The RHS describes glasshouse red spider mite (two-spotted spider mite) as yellowish-green with two dark patches, about 0.5 mm long. Look for white cast skins and spherical eggs on the underside. A 10× hand lens makes them visible.
• Webbing. Fine silk along the leaf underside, the midrib or where the blade meets the stalk. UC IPM notes that webbing separates spider mites from aphids and thrips, which also feed on undersides.

For a quick test, hold white paper under a leaf and tap it. UC IPM notes that mites knocked onto paper move around rapidly. Specks that crawl are mites. Specks that stay still are dust or debris.

Be sure mites are present before you treat. UC IPM points out that mites are sometimes gone by the time damage is noticed. Old stippling stays on the leaf even when the colony has left.

Why Polly gets mites indoors

UC IPM notes that spider mites build up fastest in hot, dusty conditions and on water-stressed plants. Iowa State University Extension’s houseplant spider mite article adds that dry indoor winter air and reduced plant vigor favor mites. The RHS Alocasia growing guide says low humidity can attract red spider mites to Alocasia.

So a Polly near a heater, in a dry room, or allowed to wilt between waterings is the plant to check first.

Treat spider mites on Polly

1. Isolate the plant. UC IPM notes that female mites disperse to other plants as leaf quality declines. Move Polly away from your other houseplants until the colony is gone.
2. Wear gloves. The RHS advises gloves because Alocasia sap irritates skin. The ASPCA lists Alocasia as toxic to dogs, cats and horses because of insoluble calcium oxalates.
3. Remove the worst leaves. Iowa State suggests pruning heavily infested portions before control. On Polly, take off only leaves that are mostly bronzed or webbed. Cut them at the base.
4. Wash the plant. Iowa State recommends a forceful spray of water in a bathtub or shower to dislodge mites. Aim at every leaf underside and the stalk joints. UC IPM suggests a water spray on leaf undersides at least once a day while plants are infested.
5. Use soap or oil if mites persist. UC IPM recommends insecticidal soap or insecticidal oil, including neem or other plant-based oils. Both must touch the mites, so cover the undersides completely. Repeat applications may be required.
6. Test first. UC IPM warns that soaps and oils can injure some plants. Spray one Polly leaf, wait several days, then treat the whole plant. Do not spray a wilted plant or one above 32 °C (90 °F).
7. Recheck weekly. Look under two or three leaves with a hand lens. Judge success by new leaves that open without fresh stippling.

Iowa State advises buying commercial insecticidal soap rather than dish detergent. Concentrated or grease-cutting detergents can harm plants. Follow every product label.

Avoid broad-spectrum insecticides aimed at other pests. UC IPM notes that some organophosphates, pyrethroids and carbaryl can trigger spider mite outbreaks. Some kill mite predators, and some stimulate mite reproduction.

When to use predatory mites or start over

The RHS names Phytoseiulus persimilis as the most commonly used biological control for red spider mite. It is sold by mail order and feeds on all mite life stages. UC IPM suggests lowering a heavy infestation with soap first, then releasing predators.

Iowa State notes that a small, heavily infested plant is often easier to discard than to rescue.

Prevent the next infestation

• Inspect leaf undersides each time you water, especially in winter.
• Keep Polly evenly watered so it does not wilt. UC IPM links water stress to mite damage.
• Raise humidity around the plant. Our Alocasia humidity guide explains how to measure it.
• Wipe dust off the leaves. UC IPM links dusty conditions to mite outbreaks.
• Check new plants with a hand lens before they join your collection.

For general care, see the Alocasia care guide and our spider mite identification and treatment guide. The Alocasia Polly hub collects our other Polly pages.

References

• Missouri Botanical Garden Plant Finder: Alocasia × amazonica ‘Polly’
• NC State Extension Gardener Plant Toolbox: Alocasia × mortfontanensis
• NC State Extension Gardener Plant Toolbox: Alocasia
• UC Statewide IPM Program: Spider Mites Pest Note
• Iowa State University Extension and Outreach: Spider Mites on Houseplants
• RHS: Alocasia Growing Guide
• RHS: Glasshouse Red Spider Mite
• ASPCA Animal Poison Control: Alocasia