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Wheat Streak Mosaic Virus Threat

Update August 11, 2010

NOW IS TIME TO MANAGE WHEAT STREAK MOSAIC

Wheat streak mosaic virus (WSMV) was severe in a number of wheat fields in North Dakota this year.  The virus was confirmed in 71 wheat samples sent to the NDSU Plant Diagnostic Lab, with a majority of these samples from counties in the north central region of the state.  Keys to managing this disease include understanding its life cycle and directing steps to break the cycle.

Virus and Mite Carrier:  The virus causes yellowing and mosaic streaking of the leaves (Picture 1), stunting of the plant, and potentially large yield losses.  The virus is transmitted from plant to plant by the tiny wheat curl mite.  This mite, only 1/100 of an inch long, needs a green “bridge” to live, reproduce, and survive.  The mite can feed, transmit the virus, lay eggs, and complete its cycle within 7-10 days under warm temperatures of 70 degrees Fahrenheit or greater.  Starting with one mite, a population of 3 million mites could potentially be produced within 60 days.  These virus transmitting mites move from plant to plant by wind.  Although mites can be spread a distance of greater than one mile, severely infected fields generally cause problems in fields within one-half mile of the source field.  Insecticides or miticides will not control wheat curl mites, and few adapted varieties have some levels of resistance to the mite or virus.

Pest2

Leaf streak and mosaic symptoms of wheat streak mosaic in young winter wheat

Mite Hosts:  The most favored hosts for mites are all the wheat crops, winter, spring or durum.  Grassy weeds such as Downy brome and smooth crabgrass are good hosts, and corn, cheat and Japanese brome are fair hosts.  Barley, rye and foxtails are poor hosts for the mite, but have been known to be infected with the virus.   Mites will feed on corn kernels and can move from green corn into adjacent winter wheat crops.

Wheat Streak Management:  Wheat streak mosaic disease is managed by breaking the life cycle of the mite through two key cultural practices: 1) controlling volunteer wheat and grassy weeds at least two weeks prior to planting; and 2) use of appropriate planting dates.  Prior to planting winter wheat this fall, the field to be planted and adjacent fields should be free of any wheat volunteers or grassy weeds.  This is generally accomplished with burn-down herbicides applied at least two weeks prior to planting, to assure complete weed control prior to emergence of the new wheat crop.  If no host is available in the field, the mite will die.   The second step, date of planting, also is very important.  Planting winter wheat too early in the fall generally results in emergence of the new winter wheat crop when mites are still very active, because of warm temperatures.  Generally, NDSU recommends planting winter wheat in northern tier counties within the first two weeks of September, and in more southern counties, the last two weeks of September.  No volunteer winter wheat should ever be left standing over winter as a potential crop.  Picture 2 is evidence of the potential devastating effects of leaving volunteer winter wheat to infect wheat crops the following spring.

Pest3

Leaf streak and mosaic symptoms of wheat streak mosaic in young winter wheat

Reasons for More WSMV in 2010:  Wheat streak mosaic virus was severe in 2010 because the late harvest made it difficult for producers to kill volunteers and weed hosts with herbicides a solid two weeks prior to planting winter wheat in 2009.  Early planted winter wheat emerged in September when warm weather caused higher mite activity.  Winter wheat planted at the end of September or later emerged in October, which was considerably colder than September and led to decreased mite activity and less spread of the virus.  The abundant snow cover during the winter had two adverse consequences.  It allowed the wheat curl mite and infected spring wheat to survive better and further spread the disease.  Producers in high risk areas did get some relief in May as cooler temperatures allowed the wheat to grow faster than mite populations. 

Sources:  Marcia McMullen, NDSU Extension Plant Pathologist; Dan Waldstein, NDSU Extension Area Specialist, North Central REC, Minot.

Udate July 8, 2010

The wheat streak mosaic virus cases in northwest Ward and western McHenry Counties were confirmed by the diagnostic lab.  Symptoms of this disease were also found in a wheat field in SE McHenry County.

Update May 30, 2010

Wheat Streak Mosaic Virus in Spring Wheat: Wheat streak mosaic virus (WSMV) symptoms were observed in spring wheat fields in the Kenmare (NW Ward County) and Sawyer (McHenry County) areas.  The fields in the Sawyer area had flag leaf infections and the Kenmare field was in the jointing stage.  Similar to Barley yellow dwarf virus, yield loss is approximately 5% with infections at the flag leaf stage and 20% at the jointing stage (Marcia McMullen, Extension Plant Pathology). 

The wheat curl mite that spreads this virus completes an entire life cycle in as little as 7 days when temperatures are in the 70’s.  The combination of the warm weather and a maturing winter wheat crop increases the likelihood of the virus being spread from field to field.  As green wheat tissue turns brown, the wheat curl mite moves out of protected areas of the wheat plant to volunteer wheat or adjacent wheat fields.  The wheat curl mite is primarily spread by wind.  Although mites can be spread by wind distances greater than one mile, the highest risk is to adjacent fields one-quarter to one-half mile from severely infected fields.  Insecticides registered on wheat are not an effective tool for wheat curl mite management.  Mites are in protected areas of the plant and reproduce rapidly so populations recover quickly from insecticides and miticides that are well below the 100% efficacy necessary for control.  The best management practice for reducing the spread of WSMV is to eliminate the volunteer wheat food source for the mites through herbicide use or tillage.  In addition, avoiding wheat on wheat rotations will reduce the spread of WSMV from one season to the next. 

Update May 06, 2010

Wheat streak mosaic virus has been confirmed in winter wheat fields in Bottineau, Renville, Rolette, and Ward counties. Our observations have led us to believe that winter wheat planted prior to Sept 25, 2009 is at the highest risk for infection. We have also found symptoms of this virus in spring wheat volunteers in the area.

Producers are potentially at a higher risk for infections in spring wheat and durum fields this growing season because of over wintering wheat volunteers. The key to successful management is control of volunteers with herbicides two weeks prior to planting.

For more information click the links below:

Wheat streak mosaic document in pdf format

KMOT News Story

or call the North Central Research Extension Center at (701) 857-7682.

Sources:

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