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Different viruses can produce similar symptoms in wheat, as is the case with wheat streak mosaic virus and barley yellow dwarf virus. Diagnostic differences between these viruses include the pattern in the field in which they appear; where wheat streak occurs on the field border and moves inward, and barley yellow dwarf virus moves out in a ring shape from the point of infection. Also, yellowing from barley yellow dwarf virus has less of a streaking appearance and more of an overall yellowing of leaf tissue, starting from the leaf tip down.
Images

Image credits
http://www.usask.ca/agriculture/plantsci/winter_cereals/images/chapt22/fig05.jpg
Possible causes
Crop type