The University of Tennessee has fielded a number of calls from folks who believe that they are seeing more metrbuzin injury on wheat this fall than in previous years. Larry Steckel, Extension iweed specialist, University of Tennessee, spent a good part of a day last week rating metribuzin tolerance in a number of county wheat trials scattered around West Tennessee to help address this question.
In those trials, a 6 foot band of metribuzin was sprayed 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 a 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 not participate in UT's testing program, so Steckel could not speak for the tolerance of their varieties.
After walking these fields as well as some other production fields, what Steckel thinks 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 he has 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. His 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.