Osprey
(mesosulfuron methyl) is a foliar-applied herbicide used to
manage weedy grasses after wheat emergence. Although
many Kentucky growers have been impressed with its ability to
control such problem weeds as Italian ryegrass and annual
bluegrass, there have been isolated cases where Osprey injured
wheat, particularly when it was applied near the time of
topdressing nitrogen fertilizer.
The Kentucky Small Grain Growers Association
supported a three-year research project beginning in the fall
of 2006 to evaluate wheat response when nitrogen fertilizer
was topdressed at different times relative to spring
application of Osprey. Liquid nitrogen (28%) was applied at
the rate of 40 gallons/A (i.e. 120 units of N/A) with Chafer
stream bars or TeeJet stream tips. Depending on the study, the
timings of nitrogen were made at weekly intervals ranging from
21 days prior to Osprey to 21 days after Osprey. Osprey was
applied early to mid-March in water at a spray volume of 20
GPA with 8003 flat fan tips. Each nitrogen timing had a
duplicate set of plots, with one set of plots receiving Osprey
and the other set of plots without Osprey as a check for
comparing wheat response to the herbicide.
Wheat injury in the form of stunted plants and
chlorotic and necrotic foliage was greatest when Osprey was
applied the same days as nitrogen fertilizer. Discoloration of
wheat foliage was temporary and did not last beyond 4 weeks
after Osprey. Stunting tended to occur more often when
nitrogen was topdressed the same day as Osprey, or earlier,
compared with topdressing after Osprey. The freezing
temperatures in April of 2007 distorted treatment effects on
end-of-season growth and yield. The only treatments where
Osprey limited wheat yield in the second study was when
nitrogen was topdressed the same day as Osprey and seven days
after the herbicide.
Based on UK research, similar results have
occurred with PowerFlex (pyroxsulam). Both Osprey and
PowerFlex are foliar-applied herbicides used to manage weedy
grasses after wheat emergence. Both products are an
Acetolactate Synthase (ALS) inhibitor that can injure wheat;
consequently, they are formulated with a safener. PowerFlex is
a relative new product; consequently, growers have had less
experience with it compared with Osprey.
