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How to Manage Pests
UC Pest Management Guidelines
Onion and Garlic
Bulb Mites
Scientific names: Rhizoglyphus spp., Tyrophagus spp.
(Reviewed 1/07,
updated 1/07)
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 to 1 mm) long. They have four pairs
of short brown legs and look like tiny pearls with legs. They generally occur
in clusters inhabiting damaged areas under the root plate of onion bulbs or
garlic cloves. 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 bulbs by penetrating the outer layer of tissue and
allowing rotting organisms to gain entry. This pest is most damaging when plant
growth is slowed by cool, wet weather. Bulb mites can reduce plant stands,
stunt plant growth, and promote rot of bulbs in storage. On seeded onions, they
can cut off the radicle before the plant becomes established.
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. Avoid planting successive onion or garlic crops.
Flood irrigation or heavy rains during the winter may reduce mite levels in the
soil. Garlic growers must insist on clean seed cloves. Hot water treatment of
seed garlic before planting may reduce mite infestation.
Monitoring and Management
Decisions
No specific monitoring methods are available. Use a microscope to
examine fragments of undecayed vegetation in the soil or volunteer onions or
garlic for the presence of the mites.
Treatments are generally
preventative and should be considered for fields that are high in vegetative
matter or that have had previous bulb mite problems. No treatment thresholds
exist.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
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| When choosing a
pesticide, consider information relating to environmental impact.
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| PREPLANT |
| A. |
METAM SODIUM* |
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(Vapam) |
50–75 gal |
48 |
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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 bulb.
Fumigants such as metam sodium
are a prime 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: Onion and Garlic
UC ANR Publication 3453
Insects and Mites
R. L. Coviello, UC Cooperative Extension, Fresno Co.
W. E. Chaney, UC Cooperative Extension, Monterey Co.
S. Orloff, UC Cooperative Extension, Siskiyou Co.
G. J. Poole, UC Cooperative Extension, Los Angeles Co.
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