For the past couple of years during the fall, Arkansas has applied for a Section 18 with the EPA for mesosulfuron-methyl (Osprey) for the control of Hoelon-resistant ryegrass. We were denied those requests based on the fact that Osprey was a new compound not registered for another crop or use in the United States.

Bayer Crop Sciences now has a full Section 3 label for Osprey for use in winter wheat. In our trials, Osprey applied at 4.75 ounces per acre with both a 0.5 percent nonionic surfactant and 1.5 pints per acre of 32 percent nitrogen or 1 percent MSO as an adjuvant has consistently provided over 90 percent control of both Hoelon-resistant and susceptible ryegrass.

In addition to ryegrass, Osprey will suppress or control many broadleaf weeds, including vetch, shepherds-purse, mustards, henbit and buttercup. It is an excellent wild oat material.

Osprey is a member of the same class of chemistry as Classic, Peak, Harmony Extra and both the active ingredients in Finesse herbicides. Unlike these compounds, however, Osprey has shown very little in the way of residual activity.

There are few rotational restrictions to Osprey and for all intents and purposes it should be considered a material with post activity only.

Osprey is labeled to be rain-fast in four hours. Both the company and the university recommends you apply Osprey in the fall to actively growing ryegrass somewhere between the one-leaf and two-tiller growth stage. Early control of ryegrass is essential to maintain maximum wheat yields.

In circumstances where a fall application is missed, however, it will be possible to apply Osprey until just prior to jointing. So, salvage ryegrass applications are labeled, but not recommended.

We have some limited data on spraying larger ryegrass with Osprey, and control has been adequate.

I prefer applications be made late in the fall after most of the ryegrass has germinated but before temperatures get too cold. At our locations, this is typically the two-tiller stage on ryegrass. Because Osprey offers no residual control, spraying later in the fall will help insure the most bang for your buck.”

One advantage that Osprey has over Hoelon is that you can tank-mix Osprey with several broadleaf herbicides without fear of antagonism. The label restricts tank-mixes with Clarity, 2,4-D, and Sencor. Harmony Extra, Express and Finesse and others are approved. We have observed no antagonism in our trials over the past two years.

In those fields that have both Hoelon-resistant ryegrass and wild garlic, it will probably be necessary to make two applications, one for ryegrass in the fall and one for garlic in the spring, because the treatment windows do not match up well.

For some time now Finesse herbicide has been an option for Hoelon-resistant ryegrass where limited rotational crops is not a concern. You must follow Finesse-treated wheat with STS soybeans. Another problem with using Finesse is that it is applied pre-emergence and requires immediate rainfall for good activity on ryegrass. When rainfall occurs, control of ryegrass is excellent with Finesse. When rainfall is delayed, ryegrass control is inadequate.

It is my understanding that the cost of 4.75 ounces per acre of Osprey will be set similar to 1.33 pints of Hoelon. The cost of Finesse is significantly less at around $6 per acre. One option on Hoelon-resistant acres would be to use $6 worth of Finesse and see if you get a rain before you automatically invest in Osprey.

Due to Osprey's lack of residual, Hoelon is probably still the best option for ryegrass control if the ryegrass is not resistant. Of course, you may want to consider a rotation to Osprey herbicide if you have used Hoelon for several years in a row to prevent the buildup of Hoelon-resistant ryegrass on your farm.

Finally, it is my understanding that BASF has some renewed interest in labeling Prowl H2O herbicide for winter wheat. Prowl is not currently labeled for use in wheat. I have been looking at Prowl on wheat for around seven years now and results have often been inconsistent on ryegrass. Like Finesse, activity depends on rainfall and there are concerns about crop safety.

We have evaluated Prowl applied at 1 pound and 2 pounds of active ingredient per acre, both pre-emerge and delayed pre-emerge. Because of the relatively low cost of Prowl and the lack of rotational issues, it would be worth a roll of the dice to try and get enough ryegrass control to get by with just a Prowl application.

Our data suggests you might do it in one year of three.

In addition to ryegrass control Prowl also controls henbit, mustards and many other small-seeded winter annual broadleaf weeds.

We have also looked at Prowl as a tank-mix partner with Hoelon or Osprey. These treatments have typically looked pretty good, and we will continue to look at them again this fall. However, I have been told it will be 2007 at the earliest for a label for Prowl on wheat.


Bob Scott is the University of Arkansas Extension weed specialist. e-mail: bscott@uaex.edu