How to Manage Pests

UC Pest Management Guidelines

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 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.

DAMAGE

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.

MANAGEMENT

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)
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.
PREPLANT
A.	METAM SODIUM*
	(Vapam)	50–75 gal	48	—
	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.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
*	Permit required from county agricultural commissioner for purchase or use.
—	Not applicable

PUBLICATION

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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