Bulb Mites (Acarid Mites)

These mites infest bulbs and host debris during storage and in the field. Note that bulb mites (family Acaridae) are a different pest than bulb scale mites, which are thread-footed mites (Tarsonemidae) Bulb scale mites are too small to be seen with the naked eye, unlike with the larger bulb mites discussed here.

Bulb mites are whitish with brownish spots and brown, stubby legs. At maturity they are about 1/50 to 1/32 inch (0.55–0.75 mm) long; immature stages are smaller. They are slow moving, oval shaped, and sometimes mistaken for insect eggs unless examined with a binocular microscope or high-powered hand lens and sufficient lighting. They feed between bud scales and in hollowed out and decomposing portions of bulbs and sometimes on basal stems, rhizomes, or roots. Egg to adult development time (1 generation) occurs in about 10 days at 80°F.

Bulb mites feed on underground parts and contribute to increased infection and damage from soil-dwelling, plant-pathogenic bacteria and fungi. Mites and pathogens in combination cause infested parts to become soft and decayed during storage or in the field. Bulb mites are associated with spread and increased incidence of Fusarium, Pseudomonas, and Stromatinia diseases of bulbs. Bulbs attacked include those of freesia, hyacinth, lilies, narcissus, and onions. Freesia bulbs are particularly affected because they require high-temperature storage to break dormancy, and higher temperatures shorten mite generation time and increase their abundance. In lilies, mite-feeding underground stunts growth and feeding at the soil level (on basal stems) causes aboveground parts to topple. On peony, underground rhizomes are infested.

Bulb mites are managed with cultural and chemical controls.

Biological control has not been investigated.

Avoid injuring bulbs and other underground parts during digging, handling, or storage; injuries promote attack by mites and plant pathogens, and pathogen infection promotes bulb mite infestations. To minimize infestations, prevent disease development in hosts by providing adequate drainage and appropriate irrigation. Use pasteurized or sterile planting media and disease-resistant cultivars. Apply fungicides when warranted. Remove or in the field deeply bury crop debris and otherwise practice good sanitation because bulb mites can persist for long periods solely on decaying crop residue. Fallow fields, rotate to non-host crops, temporarily flood fallow fields, and use flood irrigation, which also reduce bulb mite abundance.

Heat treatment

Bulbs can be disinfested of mites by holding them for 24 hours at 100% relative humidity and 105.5°F. Aerated steam and hot water are highly effective for disinfesting mites and other pests from bulbs, corms, dormant stem cuttings, and tubers. First test small batches of each cultivar to determine control efficacy and plant tolerance to heat treatment before applying the method to large portions of the crop. A general recommendation is to presoak bulbs, corms, or rhizomes for 2 to 3 hours or overnight in 75°F water containing a wetting agent before immersing them in 111°F water for about 1-1/2 hours. Cool plants immediately afterward with clean, cold water; dry them thoroughly in warm air or sunshine, then store them under cool, low-humidity conditions until plants are used. See Control Pests by Heat Treatment of Plants in Nurseries for specific guidelines by crop.

Cultural controls including heat treatment are organically acceptable management methods. Dusts or sprays of the mineral sulfur are also acceptable for organic production.

Thoroughly clean bulbs, dip them in a sulfur fungicide solution, and dry them following harvest. Sulfur controls bulb mites as well as fungal diseases during storage. CO₂ fumigation can be useful if bulbs are held long enough in the absence of free oxygen.

Selected Products Registered for Greenhouse or Nursery Ornamentals