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How to Manage Pests
UC Pest Management Guidelines
Lettuce
Bulb Mites
Scientific Names: Rhizoglyphus
spp., Tyrophagus spp.
(Reviewed 8/07,
updated 8/07)
In this Guideline:
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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.
Cultural Control
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.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
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(hours) |
(days) |
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| When choosing a pesticide, consider information relating
to the impact
on natural enemies and honey bees and environmental impact.
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| PREPLANT |
| A. |
METAM SODIUM* |
50–75 gal |
48 |
0 |
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(Vapam) |
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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), which are a major air quality issue. Fumigate
only as a last resort when other management strategies have not been successful
or are not available. |
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UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450
Insects and Other Arthropods
E. T. Natwick, UC Cooperative Extension, Imperial Co.
W. E. Chaney, UC Cooperative Extension, Monterey Co.
Acknowledgment for contributions to the insects and mites section:
N. C. Toscano, Entomology, UC Riverside
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