Identification

Acarid bulb mites are shiny, creamy white, bulbous mites that range in size from 1/2 to 1 mm long. They are relatively large in comparison with most other pest mite species. They have four pairs of short brown legs and look like tiny pearls with legs. Acarid bulb mites occur in clusters and infest flower crop bulbs such as daffodil, freesia, gladiolus, lily, and tulip in storage and in the field. They are also found inhabiting damaged areas under the root plate of onion bulbs or garlic cloves or in the crown of spinach.

Wheat curl mites and dry bulb mites (eriophyid mites in the family Eriophyidae) are smaller and more elongate than Acarid bulb mites. These mites are microscopic, white, wormlike organisms about 1/4 mm long. They have four legs that are located near the head. In addition to onion and garlic, the dry bulb mite also feeds on liliaceous bulbs such as tulips. The wheat curl mite primarily feeds on cereal grains and wild grasses but occasionally feeds on onion and garlic as well.

Damage

Acarid bulb mites are most damaging in cool, wet weather, when plant growth is slow. On seeded onions, mites can cut off the radicle before the plant becomes established. On spinach, they penetrate the developing leaves and distort the growth. They thrive in association with bulb and root diseases. Mites damage bulbs by penetrating the outer layer of tissue and allowing rotting organisms to gain entry. Plant growth may be reduced and bulbs may rot in storage or in the field. Infested fleshy bulb scales commonly turn reddish brown. Bulb mite-infested roots, rhizomes, or basal stems can become soft and decayed.

Dry bulb mites and wheat curl mites are primarily a pest of stored bulbs. Their feeding during storage produces sunken brown spots and streaks on garlic clove. Heavy infestations result in streaking and twisting of garlic leaves and reduce plant stand and yield. Damage from these mites on stored bulbs is rare in California, and the dry bulb mite more commonly infests onion and garlic than the wheat curl mite.

Solutions

Use clean seed cloves when planting garlic. Inspect bulbs carefully before planting for signs of bulb mites, and destroy any that are infested, decayed, or are soft when squeezed. Avoid injuring bulbs during digging, handling or storage. Injuries promote attack by diseases and mites. If storing bulbs, examine them carefully for signs of mites and disease.

Rapid crop rotation fosters the survival of mites on leftover vegetation. Avoid planting onion or garlic immediately after Brassica species, corn, grains, or grasses and avoid successive plantings. After harvest, clear all vegetation to allow organic matter to decompose; this reduces populations of the mite. Flood irrigation or heavy rains during the winter may reduce mite levels in the soil.

Pesticide applications are not practical for Acarid mites in home garden situations and generally not necessary for dry bulb mite and wheat curl mite.