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False spider mites

Also known as Flat mites, Tenuipalpidae, Brevipalpus mites, Phalaenopsis mite (Tenuipalpus pacificus), Orchid mite (Brevipalpus californicus)

PestHarmful
Flat mite (Brevipalpus phoenicis), a false spider mite Photo: Courtesy, Erbe, Pooley: USDA, ARS, EMU. "All of the micrographs on the web site are in the public domain and can be freely used." --Christopher Pooley. · Public domain

In short

False spider mites, or flat mites, are very small, flat, slow-moving mites that feed on leaf undersides near the midrib and veins. They make no webbing, and on orchids they leave pitted, silvery patches that turn rusty black or brown and scabby. Several Brevipalpus species transmit plant viruses.

How it looks

About 0.3 mm long, smaller than spider mites, brick-red to yellow, with a flattened, egg-shaped body that has a net-like pattern on the back. They move very slowly. Eggs are bright red, elliptical, and laid in leaf folds or along the midrib, often in dense clusters. Life stages are egg, larva, protonymph, deutonymph and adult; white shed skins show up against damaged tissue.

Signs

Pock-marked leaf surfaces that turn silvery and then rusty black; brown, scabby discolouration spreading out from both sides of the main vein; general yellowing when numbers are high; premature ageing of leaves and occasionally deformed growth. Thin-leaved orchids suffer more than thick-leaved ones.

Life cycle

A generation takes three to eight weeks, with several overlapping generations a year. Mites disperse on air currents.

Prevention

  • Inspect the undersides of new orchids and other hosts along the midrib with a hand lens before buying.
  • Quarantine new plants, since slow-building populations are easy to miss.

Treatment

Start with the first step and move down only if the problem persists.

  1. Isolate affected plants and remove the worst leaves.
  2. Predatory mites are sold for biological control of false spider mites.
  3. Horticultural oil or insecticidal soap, applied to leaf undersides three times at five- to seven-day intervals, gives suppression; follow the product label.
  4. Products based on spinosad or avermectin-class miticides are further options; follow the product label.

Pros and cons

Cons

  • Damage builds slowly and is often noticed late.
  • Some Brevipalpus species transmit plant viruses.

Look-alikes

Spider mites
Produce fine webbing, move faster and cause pale stippling rather than scabby brown patches along the midrib.
Thrips damage
Silvering comes with dark varnish-like droppings, and slender insects are present.

Affected plants

Orchids (including Phalaenopsis and Oncidium), citrus, papaya, pomegranate and many greenhouse ornamentals.

Sources

  1. Orchid Insect and Mite Pests in South Florida (ENY2114) — UF/IFAS
  2. False spider mites — Koppert
  3. Tenuipalpidae — Wikipedia

Written in our own words from these sources. Check a product label before using any treatment.