For farmers with Hoelon-resistant ryegrass problems, there is now Osprey. No, not a bird, but a new herbicide featuring new chemistry.
Bob Scott, weed scientist with the University of Arkansas Cooperative Extension Service, says Osprey has just been labeled for use in wheat. He says the U of A Division of Agriculture had petitioned the Environmental Protection Agency for Section 18 approval to use Osprey in wheat.
"We've been using Hoelon in Arkansas for ryegrass control for nearly 20 years, and this has resulted in the development of Hoelon-resistant ryegrass," Scott says. He estimated that about 15% of Arkansas ryegrass is resistant to Hoelon.
"Osprey has a different chemistry and a different mode of action. It's effective on both regular ryegrass and Hoelon-resistant ryegrass. It also suppresses many broadleaf weeds, which Hoelon doesn't."
Another extension weed scientist, Ken Smith, says Hoelon, the "old standby" for controlling ryegrass, works on contact and has some residual control activity.
"It was really good until we started using it continually," he says, "and the herbicide resistance built up. Osprey works on all ryegrass, but it has no residual activity. With Osprey, farmers will have to wait until the ryegrass emerges to use it."
When applied at a 4.75-ounce per acre rate, Osprey has consistently provided more than 90% control of both Hoelon-resistant and susceptible ryegrass.
Scott says Osprey is a member of the same class of chemistry as Classic, Peak, Harmony Extra and both active ingredients in Finesse herbicides. Osprey has specific adjuvant requirements, whereas Hoelon doesn't. In an herbicide product, an adjuvant is a material mixed with the product to make it work better.
The extension service and the maker of Osprey recommend that farmers apply Osprey in the fall to actively growing ryegrass between the one-leaf and two-tiller growth stage. Early control of ryegrass is essential in maintaining maximum wheat yields.
"One advantage Osprey has over Hoelon is that you can tank-mix Osprey with several broadleaf herbicides without fear," Scott says.
He says that the cost of 4.75 ounces of Osprey for an acre will be about the same as using the recommended 1.33 pints of Hoelon. The cost of Finesse, another ryegrass herbicide, is significantly less at about $6 an acre.
Scott says farmers can collect ryegrass seed and send it the University of Arkansas to determine if the grass is Hoelon-resistant. He says county extension agents can advise farmers and send in the seeds for testing.
Scott says Finesse, a pre-emergent herbicide, works well in controlling Hoelon-resistant and non-resistant ryegrass in wheat. In addition to controlling ryegrass, it controls the widest spectrum of weeds in wheat of any herbicide, according to Scott.
"It's applied pre-emergent to the soil immediately after wheat planting and before ryegrass emergence," Scott says. "It requires rainfall for activation, which can be a limiting factor. It's economical and effective, and it can be a good option for farmers infested with resistant grass."
If it doesn't rain to activate Finesse, Scott says, a farmer will have to go back in and apply Osprey.
"If a farmer uses Finesse on wheat, he or she must plant STS soybeans the following year instead of conventional soybeans."
For more information on wheat and weeds, contact your county extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.