Tuesday, August 15, 2017

Wheat Streak Mosaic Virus Prevention

Jesse Fulbright, MSU Liberty County Extension

I know that as harvest begins wrapping up in the coming weeks that everyone will be turning their attention to fall seeding, if we ever get some moisture.  If you or a neighbor had wheat streak mosaic virus, or even if you didn’t, please make sure that the green bridge is eliminated this fall.  Wheat curl mite, the vector of WSMV, will continue moving from harvested grain, volunteer, cheatgrass and other grasses into new and green grasses, particularly volunteer and planted winter wheat, until a major frost event. 

Please make sure that you give those plants plenty of time to die before planting back in with winter wheat.  This is for wheat streak mosaic virus consideration as much as anything.  Extension’s recommendation is that you spray 2-3 weeks before planting back.  While growers might not find this realistic, please wait as long as you can before going back in with winter wheat seed.  Otherwise there is the risk of a green bridge occurring.
If you have volunteer grains, grazing hailed/volunteer cereal grains and not terminating the remaining volunteer creates a high risk disease situation.  You can graze, but you need to terminate the volunteer with tillage or glyphosate and allow the plant material to die before planting a new crop.  This scenario can provide inoculum for neighboring crops, since the mite can travel in wind.  So, when making grazing decisions, consider neighbor planting decisions.

Good volunteer and grassy weed control is CRITICAL in WSMV-affected areas, and is a good best management practice in all areas, particularly those hit by hail after mid-milk in cereals.  At this point the seed is capable of germinating and creates volunteer.
Hosts vary in their ability to support mite and virus replication.  The best host by far is spring wheat, followed by winter wheat and barley.  A somewhat distant third is downy brome or cheatgrass which due to its life cycle and high populations does serve as a significant alternate host in Montana.  Then, there are numerous grassy weeds that overall are ‘intermediate/poor’ hosts of the mite and virus, but could be sources in some years if conditions are favorable.  They essentially maintain a background level of the virus and mite that we will never eliminate. 

Please contact your local county Extension office with further questions about wheat streak mosaic virus and how to better manage for it.

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