We have fielded a number of calls from folks who believe they are seeing more metribuzin injury on wheat this fall than in previous years. I rated metribuzin tolerance in a number of county wheat trials scattered across West Tennessee to help address this question.
In those trials, we sprayed a 6-foot band of metribuzin at a 6 oz/a rate and another at a 12 oz/a rate. With the 6 oz/a rate, the wheat injury consisted of some minor burning (no stand loss) and ranged from 0% to 20% depending upon the variety. Well over 90% of the varieties in these county tests showed injury at or below 10%. This is consistent with the results from previous years. What this says to me is the typical metribuzin rate used in Tennessee of 3 to 4 oz/A should not result in any kind of significant wheat injury regardless of variety. One caveat here is that Pioneer does no participate in our testing program so I cannot speak for the tolerance of their varieties.
After walking these fields as well as some other production fields, what I think is going on is a bit of an optical illusion. From the road many of our West Tennessee wheat fields look like they have great stands. Upon closer inspection though a lot of the green in these fields is poa. The poa pressure has been very heavy in most of the wheat fields that I have walked this spring.
Therefore, the main reason metribuzin-treated wheat fields look like they have thinner wheat stands than those not treated is that the poa has been removed by the herbicide. My best estimate of how this will play out is come next March the metribuzin-treated wheat fields will look much better than many of the fields that were not treated with a herbicide this fall.