How to Manage Pests

Pests in Gardens and Landscapes

Bulb mites (Spinach crown mites)—Rhizoglyphus and Tyrophagus spp.

Bulb mites are shiny, creamy white, bulbous mites that range in size from 0.5 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. 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.

Damage

Bulb mites appear to be secondary pests, attacking weakened tissue. Bulb 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. They thrive in association with bulb and root diseases. Infested fleshy bulb scales commonly turn reddish brown. Bulb mite-infested roots, rhizomes, or basal stems can become soft and decayed. On seeded onions, mites can cut off the radicle before the plant becomes established. On spinach, bulb mites penetrate the developing leaves and distort the growth.

Solutions

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. 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.

Bulb mite adult
Bulb mite adult


Statewide IPM Program, Agriculture and Natural Resources, University of California
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