Wheat Streak Mosaic & the “Green Bridge”

Wheat Streak Mosaic (WSM) is a viral disease that can infect wheat, barley, corn and many other grasses.  The virus is transmitted by the wheat curl mite, which can move by leaf rubbing or be blown from field to field by wind.  Infected plants are usually stunted and produce fewer seeds.  The earlier the infection, the greater the impact to yield potential.  Both the virus and the wheat curl mite require living, i.e. green, material in order to survive.   

The mite and virus overwinter on infected plants, which can include winter wheat or volunteer cereals. In the spring, mites multiply rapidly and can be blown to other hosts such as spring wheat, winter wheat or even volunteer spring wheat.  These hosts harbour the mite and virus over the summer.  If winter wheat is seeded near unharvested spring wheat or into fields with potential host plants, infected mites can be blown onto the winter wheat completing the disease cycle.  As long as there is green tissue (the “green bridge”) available to the mite the virus with continue with its life 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.

Wheat streak mosaic can be controlled or reduced to a minimum by following certain cultural and agronomic practices as there are no pesticides available for control of the mite or virus.  The key control method is to disrupt the life cycle of the wheat curl mite by removing the “green bridge” in the fall to try and prevent infection of the winter wheat.  Control all host plants, such as volunteer cereals, at least two weeks before winter wheat is planted as the mites cannot survive longer than ten days with no living hosts.  This would include not only the field winter wheat is to be seeded into but also adjacent fields (which may not be possible of course).  Another control method is not seeding winter wheat near immature spring wheat or other cereals. 

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