Broad mites (Polyphagotarsonemus latus) are one of the most damaging houseplant pests in UK collections, and one of the hardest to spot. You will never see the mite itself with the naked eye. What you will see is the damage: new leaves emerging twisted, glossy, downward-curled, and sometimes bronzed. They love Anthuriums, Hoyas, Peperomias, many aroids. The good news is that they are treatable, and once you know what to look for you can catch infestations early.
What Are Broad Mites?
Broad mites are microscopic arthropods in the family Tarsonemidae. Adults are around 0.2mm long, about a fifth the size of a spider mite, and translucent yellow-green. You cannot see them without a hand lens of at least 30x magnification, and even then they are easy to miss. They feed on emerging tissue at the growing tip of the plant, injecting saliva that contains a growth-regulating toxin. The toxin causes the cell distortion that gives broad mite damage its characteristic look.
They are distinct from spider mites (which produce webbing and stippling on mature leaves) and from flat mites (which cause leaf bronzing but not the same growth-tip distortion). The combination of healthy older leaves and badly malformed new ones is the giveaway for broad mites.
Life Cycle of Broad Mites
The full life cycle takes about 5 to 14 days at 20 to 25°C, which is why infestations build so quickly. A female lays up to 50 eggs in her short adult life, and males physically carry female nymphs to fresh growth, spreading damage across the plant. There are four stages: egg, larva, quiescent nymph, adult.
Two things matter for treatment timing. First, eggs are unaffected by most contact treatments, so you have to repeat applications to catch each new hatch. Second, the life cycle accelerates in warm humid conditions, exactly the environment a grow tent, terrarium or steamy bathroom provides. If you collect humidity-loving plants, broad mites should be on your watch list.
Identifying Broad Mites
Physical Characteristics
You almost certainly will not see the mites. If you have a good hand lens, look at the underside of the youngest leaf or in the growing point itself, where the mites concentrate. They are pale yellow, oval, with a faint pearly sheen, and they move slowly. The eggs are clear and stuck to the leaf surface in small dotted patterns.
What you will see is the damage. New leaves come out:
- Distorted, twisted or curled downward at the edges
- Glossy or slightly waxy, as if dipped in varnish
- Hardened and sometimes brittle
- Smaller than usual, with shortened internodes
- Bronzed or bruised on the lower surface
- Sometimes with corky scarring along the midrib
Older established leaves usually look normal, which is what makes broad mites easy to mistake for nutrient deficiency, herbicide drift, or a thrips infestation.
Where to Look
Always check the growing tip first. Pull back the youngest leaves carefully and look down into the centre of the plant where new growth emerges. Damage radiates outward from this point. Check the undersides of any newly opening leaves, where mites and eggs concentrate.
On vining hoyas, philodendrons and scindapsus, check the apical bud and the next 2 to 3 newest leaves. On rosette-forming plants like anthuriums and African violets, look right into the crown.
Where Do Broad Mites Come From?
The most common entry point is a newly purchased plant. Imported anthuriums, hoyas and tissue-culture plants are the most frequent carriers we see. They also spread on tools, hands, clothing, and on the move during repotting. They cannot fly but they do drift on air currents and they hitch rides on other insects.
This is the case for strict quarantine. Any new plant joining a collection should sit alone for a minimum of three weeks, ideally six, and be inspected weekly. See our quarantine guide for the full protocol.
Damage Caused by Broad Mites
The first sign is malformed new growth. Left untreated, the plant continues to push out distorted leaves indefinitely, the growing tip eventually aborts or dies, and side shoots are then attacked in turn. A heavily infested plant will look stunted and bonsai-like with hardened, twisted leaves and no soft new growth at all.
Some species suffer more than others. Anthuriums, Hoyas, Peperomias, and aroids in general show damage badly. Tougher-leaved plants like Sansevieria and most cacti are rarely affected.
How to Get Rid of Broad Mites
Immediate Steps
The moment you suspect broad mites, isolate the plant. Move it to a different room, ideally with a closed door between it and the rest of your collection. Inspect everything else within 1 metre of the affected plant, and any plant you have moved, repotted or pruned alongside it in the last month.
If the damage is bad, cut off the worst-affected growth and bin it (do not compost). This removes the bulk of the mite population in one go and lets you see whether new growth comes through clean.
Hot Water Treatment
The most effective home remedy for broad mites is a brief hot water dip. They cannot survive at temperatures above 43°C, but most houseplants can tolerate brief exposure to 45 to 46°C. The protocol we use at the nursery on incoming hoyas and anthuriums:
- Heat water to exactly 46°C with a thermometer. Do not guess.
- Submerge the entire affected part of the plant (foliage and growing tip) for 15 minutes.
- Drain and return to a cool shaded spot for 24 hours before resuming normal care.
This is dramatic but effective. Test on one leaf first if you are nervous, and avoid it on plants with very thin or new leaves, which can scald. It is not suitable for orchids or African violets, where contact treatments are safer.
Contact Treatments
For plants where the hot water dip is impractical, switch to repeated contact sprays. Broad mites die quickly on contact with horticultural soap or potassium-based plant invigorators, but eggs are unaffected, so you must repeat the treatment to catch each new hatch.
We use SB Plant Invigorator diluted to label rate, applied every 5 days for 3 weeks (a minimum of five applications). Spray to wet the underside of every leaf, the growing tip, and the petiole bases. Miss spots and the infestation will rebuild.
For heavy infestations, Pepin Neem Oil added at half label rate to the SB Plant Invigorator mix increases knockdown and disrupts the moulting cycle. Do not use neem in direct sun, or on plants in active flower.
Horticultural soap is another reliable contact treatment, applied to the same schedule.
Biological Controls
For collection-scale infestations, the predatory mite Neoseiulus cucumeris (the same species used commercially in glasshouses for thrips) feeds on broad mite eggs and immatures. Release rates and conditions are specialised; if you have a grow tent or cabinet collection it is worth looking into. Amblyseius swirskii is also effective in warmer, more humid environments.
Prevention
Broad mites are difficult to keep out of a collection that frequently takes in new plants, so the strategy is early detection rather than total exclusion.
Quarantine every new plant for at least three weeks. See our quarantine protocol. Inspect the growing tip weekly.
Check the growing tip every time you water. Any glossy curled leaf coming out of the centre of a plant is a flag. Catching it on the first damaged leaf instead of the tenth is the difference between an easy treatment and losing the plant.
Clean tools between plants. Wipe scissors and tweezers with surgical spirit between each plant when pruning or propagating.
Avoid sharing soil or moss between plants. Broad mites can survive briefly off the plant in damp organic matter.
If you grow in a cabinet, terrarium or tent, the warm humid conditions accelerate infestations massively. Quarantine becomes even more important, and an early-warning predatory mite programme is worth considering.
If your new plant has come from us and you suspect broad mites, get in touch straight away. We hot-water-treat susceptible species on intake and want to know if anything has slipped through.