HIGH PLAIN VIRUS AND THE WHEAT CURL MITE
Silvia I. Rondon, Extension Entomologist
Oregon State University, Hermiston Agricultural Research and Extension Center
Email: silvia.rondon@oregonstate.edu
Introduction
High plains disease is transmitted by the wheat curl mite Aceria tosichella, the same
vector that transmits wheat streak mosaic and wheat spot mosaic. The wheat curl mite is a
common mite in the central plains of the US. In the northwest, it was first confirmed in
Idaho in 1993, in Utah in 1994, and in Washington in 1998. In Oregon, the pest is present
since the early 90’s although it wasn't of major significance until 2003.
The wheat curl mite. Picture courtesy of L. Townsend, Dept. of Entomology
The virus
□ Viruses multiply only in living hosts and cannot move by themselves. Some type
of vector is needed for viruses to move from plant to plant. The only known
vector of High Plain Virus (HPV) in corn is the wheat curl mite.
□ Both the mites and virus persist on living, susceptible plants, but not on wheat or
other grasses as they mature and dry down.
□ Wheat is the favorite habitat for the wheat curl mite. Other hosts include oats,
barley, rye and corn.
□ In corn, mites feeding cause leaves to roll up. Both dent and sweet corn cultivars
are affected.
The vector: the wheat curl mite
□ The wheat curl mite belongs to a group of microscopic plant-feeding pests.
Rondon. Corn Field Day, September 7 2006
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□ Mites are not true insects, but are closely related to ticks and spiders.
□ The wheat curl mite is white and about 1/100 of an inch long and has a sausage
shape. Requires a powerful magnifying glass to see the mite on the leaf.
□ The life stages of the wheat curl mite are: egg, two larval stages, and adult.
□ Females lay about 1 egg per day. During their life-time they lay approximately
25 eggs.
□ The minute eggs are attached to the leaves parallel to the leaf veins.
□ At 75-80oF, mite populations build rapidly. A complete cycle can be completed
in 7 to 10 days. At 32oF, development stops (diapause). All stages can survive at
least 3 months at near freezing temperatures and can survive for several days at
0oF. In the laboratory, mites can survive only about 8 hours at 75oF without food
or water.
□ Hot dry weather can reduce mite populations and virus problems significantly,
but survival of alternate hosts can prevent their complete elimination.
□ Mites crawl very slowly and depend almost entirely on wind for movement from
plant to plant. Thus, the spread of the disease is related to the dispersal of the
mite vector. They are always looking for new growth.
□ New infestations usually first occur along field margins; then they spread.
□ Mites that land on corn plants will crawl into the leaf sheaths to feed and
reproduce. As ears develop, the mites can move to feed on husks, silks, and
kernels. As the ears mature and dry, the mites will again take up positions on the
outer plant parts to be blown away.
□ The virus is carried in the mid and hind gut of both larval and adult stages.
□ Once inside the mite, the virus can be passed on to other plants during feeding.
□ The virus can be picked up during a 10 to 30 minute feeding period and remains
active in the mite for 7 to 9 days. The virus remains in the mite as it molts from
stage to stage, but cannot be passed to the next mite generation through the egg
stage.
Rondon. Corn Field Day, September 7 2006
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Mosaic Cycle (Picture courtesy Agricultural Communication, NDSU)
General Recommendations
□ Volunteer wheat and grasses should be destroyed to limit vector survival.
□ Avoid late seeding.
□ The use of acaricides or insecticides against the leaf curl mite has not resulted in
effective control.
□ Cultural practices and resistant varieties are the major tools in mite and disease
management.
OTHER MITES
Banks Grass Mite
□ Banks grass mite attacks a wide variety of grasses,
including turf, sorghum and wheat.
□ The life stages of the mite are: egg, larval stages, and
adult. Adults are similar than the twospotted spider
mites. Overwintering mites are bright orange.
□ The time required to complete a generation varies with
temperature. At 75oF is usually 10 to 20 days.
Bank grass mite (actual size at maturity, 1/60 to 1/50 inch).
Picture courtesy UF.
Rondon. Corn Field Day, September 7 2006
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□ Banks grass mites produce heavy webbing to protect colonies. Colonies usually
are found on the undersides of leaves.
□ Heavy populations can kill small plants and reduce kernel size in larger plants.
□ Insecticide applications to field margins bordering corn often are sufficient to
prevent economic damage.
Two Spotted Spider Mite
□ Tiny, spider like, located on underside of leaves that
cause yellowing or silvering of leaves. They feed on
plant juices and may contribute to early maturity and
poor quality of corn.
□ Male and female spider mites develop through the
following stages: egg, larva, protonymph,
deutonymph, and adult.
Spider mite.
Picture courtesy UF.
□ All stages can be found in web covered colonies on the
undersides of leaves. Separation of the various stages is difficult, with the
exception of the eggs. The eggs are spherical, about 0.14 mm in diameter and
clear when newly deposited. They turn opaque when incubation proceeds.
□ The adults usually have a dark spot on both sides of the body, hence their
common name. Males are slender and smaller than females, and usually the tip of
their abdomen is elongated. Dispersal of the twospotted spider mite is mainly by
infested stock. Consequently, patchy infestations ("hot spots") are characteristic
for this pest in fields. Mites also can suspend themselves on silken threads and be
dispersed by air currents.
□ Temperature and host plant quality are important determinants for egg production
as well as for the rate of development. One female may produce as many as 100
eggs during their life time; one generation may develop in about 7 days 85°F.
Rondon. Corn Field Day, September 7 2006
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