How to Manage Pests
UC Pest Management Guidelines
Onion and Garlic
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 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.
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
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
|The following materials are listed
in order of usefulness in an IPM program, taking into account impact
on natural enemies and honey bees.
When choosing a pesticide, also consider information relating to
environmental impact. Not all registered pesticides are listed. Always read label of product being used.
||COMMENTS: 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: Onion and Garlic
UC ANR Publication 3453
Insects and Mites
S. Orloff, UC Cooperative
Extension, Siskiyou County
E.T. Natwick, UC Cooperative Extension, Imperial County
G. J. Poole, UC Cooperative Extension, Los Angeles County
Acknowledgment for contributions to Insects and Mites:
R. L. Coviello, UC Cooperative Extension, Fresno County
W. E. Chaney, UC Cooperative Extension, Monterey County
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