How to Manage Pests
UC Pest Management Guidelines
Scientific Names: Rhizoglyphus
spp., Tyrophagus spp.
In this Guideline:
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. They have a wide
host range, feed on many kinds of bulbs, roots, and tubers, and can infest
bulbs in storage or in the field. Bulb 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.
Rapid rotation, from one crop to the next, fosters survival of mites on the
leftover vegetation in the soil from the previous crop. Decaying cole crops,
especially cauliflower, may harbor very high bulb mite populations. Fallow
fields to allow complete decomposition of organic matter; this reduces field
populations of the mite. 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 undecayed vegetation in the soil for the presence of the mites.
Treatments are generally preventive and should be considered for
fields that are high in vegetative matter or that have had previous bulb mite
problems. No treatment thresholds exist. Proper vegetation management and
timing of planting is key.
|When choosing a pesticide, consider information relating to the impact on natural enemies and
honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
||COMMENTS: Metam sodium injected
into the soil at 6 inches deep before planting has provided fair to good
control of bulb mites living on organic matter in the field. However, it will
not control mites brought into the field on infested bulbs. Fumigants such as
metam sodium are a source of volatile organic compounds (VOCs) but are
minimally reactive with other air contaminants that form ozone. Fumigate only
as a last resort when other management strategies have not been successful or are not available.
UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450
Insects and Other Arthropods
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects and Mites:
W. E. Chaney, UC Cooperative Extension, Monterey County
N. C. Toscano, Entomology, UC Riverside
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