How to Manage Pests
UC Pest Management Guidelines
Scientific Names: Rhizoglyphus spp., Tyrophagus spp.
(Reviewed 4/17, updated 4/17)
In this Guideline:
DESCRIPTION OF THE PESTS
Bulb mites are shiny, creamy white, bulbous-appearing mites that range in size from 0.02 to 0.04 inches (0.5–1 mm) long. They have four pairs of short brown legs and look like tiny pearls with legs. Bulb mites have a wide host range, feed on many kinds of bulbs, roots, and tubers, both, in storage or in the field. These mites can survive on decaying vegetation in the field until it is completely decomposed.
Bulb mites damage lettuce at germination only by penetrating the seedcoat as soon as germination begins. This pest is most damaging when emergence is slowed by cool, wet weather. Bulb mites can drastically reduce plant stands, especially when lettuce follows cole crops.
Rotation from one crop to the next without proper cultivation will foster mite survival on the leftover vegetation in the soil from the previous crop. Decaying cole crops, especially cauliflower, may harbor high bulb mite numbers. Fallow fields to allow complete decomposition of organic matter; this will in turn reduce mite numbers. Flood irrigation or heavy rains during the winter may reduce mite levels in the soil.
Monitoring and Treatment Decisions
No specific monitoring methods are available. Use a microscope to examine fragments of non-decayed vegetation in the soil for the presence of the mites.
Treatments are generally preventive and should be considered for fields that are high in organic matter or that have had previous bulb mite problems. No treatment thresholds exist. Proper vegetation management and timing of planting is key.
UC IPM Pest Management Guidelines: Lettuce
Insects and Other Arthropods
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects and Mites:N. C. Toscano, Entomology, UC Riverside