Host Crops
Wheat streak mosaic virus attacks barley, corn and some grasses, but is most common on
winter and spring wheat. Oats and rye may be infected but they do not appear to be
seriously damaged. Wheat is the only cereal that is seriously affected.
Biology
Wheat streak mosaic is a viral disease of wheat. The virus enters the leaves and
spreads to all parts of the plant. Infected plants are usually stunted and produce fewer
seeds, which are often badly shrivelled. The earlier the infection, the greater the effect
on the plant.
Wheat streak mosaic virus is transmitted by the wheat curl mite and by leaf rubbing.
The mite can be blown from field to field by wind.
The mite and virus overwinter on winter wheat. In the spring, mites multiply rapidly
and are blown to spring wheat or volunteer spring wheat. These hosts harbour the mite and
virus over the summer. If winter wheat is sown near unharvested spring wheat, infected
mites can be blown onto winter wheat completing the disease cycle.
Development of this disease depends on the population of mites, the presence of
virus-infected wheat plants, and sufficient moisture for good plant growth and rapid mite
reproduction. Severe outbreaks occur when there is a build-up of mites and virus on
volunteer spring wheat in fields next to winter wheat that was planted early.
Symptoms of the disease become more pronounced when temperatures climb above 10 degrees
C (50 degrees F) in the spring. Symptoms of Damage
Winter wheat rarely shows symptoms until spring. These symptoms appear on the leaves as
dashes, streaks or yellow stripes parallel to the veins. Leaves become increasingly
mottled until the green areas disappear and the leaves die. Infected plants are stunted;
the degree of stunting depends on how early the infection took place. Wheat spot mosaic
virus, which is similar to wheat streak mosaic virus, is spread by mites, has a comparable
life cycle, and may sometimes be present in winter wheat.
Wheat infected at an early tillering stage stops growing and produces few to no heads.
Infection at late tillering to early jointing stages results in head formation but the
flowers may be sterile. With late season infection during jointing to boot stage, the
flowers are fertile but kernels are reduced in size. Fall-infected winter wheat plants do
not produce grain the following season. One study found that stunted and diseased plants
yielded 78% less than healthy plants, and seed milling quality was reduced substantially.
Scouting Techniques
Mites in large populations on wheat will cause the leaf blades to curl upward and
inward. Tips of new leaves are often caught in the curled leaf above it; this may indicate
the presence of the mites and virus. A microscope or a good magnifying glass is necessary
to see the mites.
Economic Thresholds
None available.
Control Tips
This disease can be controlled or reduced to a minimum by following certain cultural
and agronomic practices. The key control method is to disrupt the life cycle of the wheat
curl mite by preventing infection of winter wheat. Mites that survive the winter on winter
wheat increase rapidly during the warm spring and summer weather and are blown to nearby
hosts.
Do not sow winter wheat near immature spring wheat or other cereals. Seed winter wheat
after spring crops are mature. Control all volunteer host plants at least 2 weeks before
winter wheat is planted including adjacent fields. The mites cannot survive longer than 10
days in the absence of living cereal plants. Plant winter wheat as late in August or
September as possible to avoid the period when mites move from late-maturing spring
cereals.
Do not reseed a severely diseased winter wheat field with spring wheat. Diseased winter
wheat plants are difficult to eliminate completely.
There are no pesticides available for the control of the mite or virus. |
