Onion Bulb Mite Reference
Page
Rhyzoglyphus
spp.
Pest
description and crop damage
Bulb mites are shiny, creamy white, bulbous,
and about 1⁄32 inch long. 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
rot organisms to gain entry. This pest is most damaging when plant
growth is
slowed by mild, 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.
Scouting
and thresholds
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
generally are 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.
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.
Management—chemical
control
1.
Soil
fumigation can help to control this pest.
Source: PNW
Insect Management Handbook
Updated April 27, 2007-jn
