Broad mites
Also known as Polyphagotarsonemus latus, Tarsonemid mite
In short
Broad mites are microscopic mites that feed on the youngest leaves and buds. Their toxic saliva leaves new growth twisted, hardened and bronzed underneath, damage that is easily mistaken for herbicide injury, nutrient deficiency or a virus. They prefer warm, humid conditions.
How it looks
Adult females are about 0.25 mm long, roughly a quarter the size of a spider mite, and cannot be seen without at least a 20× lens or a microscope. They are oval, colourless to pale brown and translucent, with a white stripe down the back. The eggs are the easiest stage to recognise under magnification: elliptical and covered in rows of whitish bumps that look like diamonds. They live on the undersides of the newest leaves, in buds and inside the distorted tissue they cause.
Signs
New leaves become twisted, curled downwards, thickened and hardened, often with bronzed undersides and puckered margins. Buds deform or drop, flowers are distorted or fail to open, internodes shorten so growth looks stunted, and the growing tip can die. The damage shows as tissue expands after feeding, so symptoms can appear after the mites have moved on.
Life cycle
Egg, larva, nymph and adult. Larvae hatch in 2–3 days and begin feeding at once, and egg to adult takes about 6–10 days in warm conditions, sometimes as little as a week. Estimates of eggs per female vary between sources, from about 20 to as many as 75.
What favours it
Development is favoured by about 21–27 °C (70–80 °F) with 80–90% relative humidity; the broad mite is a tropical species, so warm, humid homes and greenhouses suit it. It spreads on air currents, by plant contact, on hands and tools, by hitching rides on adult whiteflies, and in cuttings and other vegetatively propagated plants.
Prevention
- Buy or start from mite-free stock, and look at the newest leaves and buds of new plants with a strong lens.
- Quarantine new plants, and handle any suspect plant last, washing hands afterwards.
- Control whiteflies, which can carry broad mites between plants.
Treatment
Start with the first step and move down only if the problem persists.
- Discard severely infested plants, or cut out distorted shoots and bin them.
- Release predatory mites such as Neoseiulus cucumeris, N. californicus or Amblyseius swirskii early, before numbers peak.
- Home gardeners can use horticultural oil, insecticidal soap, neem oil or wettable sulfur, repeating as directed; follow the product label.
- Commercially, translaminar miticides are used with repeat applications; follow the product label.
Pros and cons
Cons
- Distorts flowers and new growth, often ruining ornamental value.
- Invisible to the naked eye, so infestations are usually found late.
Look-alikes
- Cyclamen mites
- Very similar damage, but cyclamen mites prefer cool humid conditions and have a parallel-sided body; a microscope is needed to tell them apart.
- Nutrient deficiency or herbicide injury
- No mites or diamond-patterned eggs on the newest leaves under magnification.
- Virus infection
- Mosaic or mottled patterns rather than hardened, bronzed, downward-curled new growth.
Affected plants
African violet, azalea, begonia, chrysanthemum, cyclamen, dahlia, Exacum, gerbera, gloxinia, hibiscus, impatiens, English ivy, jasmine, lantana, marigold, rhododendron, snapdragon, verbena, zinnia, peppers and lemons, among many other ornamentals and vegetables.
Related
Sources
- Broad Mite and Cyclamen Mite — UC IPM Home and Landscape
- Managing Broad Mites on Greenhouse Crops — UConn IPM
Written in our own words from these sources. Check a product label before using any treatment.