Bulb mites
Also known as Rhizoglyphus echinopus, Rhizoglyphus robini, Acarid mites
In short
Bulb mites are tiny, slow-moving mites that feed on bulbs, corms and other underground plant parts. They are usually secondary pests that follow injury or rot, but their feeding lets fungi and bacteria in, so bulbs soften and decay.
How it looks
Oval, shiny white to translucent mites about 0.5–1 mm long (1/50–1/25 inch) with short, stubby reddish-orange to brown legs and sometimes two brown spots on the body. They move slowly and cluster under bulb scales and where roots join the bulb, and can be mistaken for insect eggs without a strong hand lens. Crowded colonies produce a non-feeding travelling stage (hypopus) that clings to insects such as fungus gnats to spread.
Signs
Stunted plants, yellowing and distortion; soft, decaying, reddish-brown areas on bulbs and bulb scales; in lilies, stems toppling at soil level. Checking the base of a bulb with a hand lens shows the mites.
Life cycle
Egg, larva, nymph and adult. At about 25–27 °C (77–80 °F) the cycle takes only 10–12 days; each female lays up to about 100 eggs.
What favours it
Bulbs already damaged by handling, fungus gnat larvae or rot; warm, moist storage or media.
Prevention
- Buy firm, clean bulbs and discard soft or damaged ones.
- Handle bulbs carefully and store them cool and dry.
- Control fungus gnats and root rot, which open the way for mites.
- Remove plant debris and do not reuse old mix from infested pots.
Treatment
Start with the first step and move down only if the problem persists.
- Discard badly infested, soft bulbs.
- Hot-water treatment used by growers: presoak bulbs 2–3 hours in water at about 24 °C (75 °F), then immerse in water at about 44 °C (111 °F) for about 1.5 hours; temperature control matters to avoid damaging the bulbs.
- No biological control is commercially available; the predatory mite Hypoaspis aculeifer has shown promise in trials.
- Chemical options are few and poorly tested; sulfur dust or wettable sulfur is an organically acceptable option for growers — follow the product label.
Pros and cons
Cons
- Speeds up bulb rot and spreads with fungus gnats.
Look-alikes
- Fungus gnat larvae
- Much larger (up to about 6 mm), worm-like, with a shiny black head.
- Springtails
- Harmless six-legged hexapods that jump when disturbed.
- Soil predatory mites
- Brownish, fast-moving mites that hunt other small soil animals.
- Bacterial soft rot
- Soft, smelly bulb rot that can occur without mites.
Affected plants
Amaryllis (Hippeastrum), crocus, freesia, gladiolus, hyacinth, lily, narcissus, peony rhizomes, tulip, garlic and onion.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.