Bob Scott says that when it comes to problem weeds in winter wheat in Arkansas, ryegrass probably ranks No. 1, No. 2 and No. 3.
“About eight years ago, Ford Baldwin (former Arkansas Extension weed scientist) and others determined we had Hoelon-resistant ryegrass in a field near Willow Beach, Ark.,” says Scott. “In fact, they put out 20 pints of Hoelon on that field. It killed the wheat, but the ryegrass lived.”
The discovery led to an Arkansas Extension Service survey of wheat growers across the state. Of the samples submitted in the survey, 60 percent were Hoelon-resistant to some degree, according to Scott, Extension weed specialist for Arkansas.
“Weed scientists at the University of Arkansas have determined we have Hoelon-resistant ryegrass in every wheat-growing county in Arkansas,” he said. “So you can see ryegrass control is a widespread problem.”
That's why Scott and other specialists are happy to see that growers have a new postemergence herbicide that can be used to control ryegrass and other weeds when they begin planting wheat this fall.
Osprey, the new herbicide developed by Bayer CropScience, received a Section 3 registration from EPA on March 31 and was applied on about 250,000 acres of spring wheat that had just been planted in Oregon. Mid-South growers will see the herbicide for the first time this fall.
“We put in for Section 18 emergency exemptions for Osprey while it was a numbered compound,” said Scott, speaking at an Osprey kickoff meeting in Memphis, Tenn. “EPA denied those, but now we've got it, and we believe growers will use it.”
Osprey can be applied postemergence from emergence up to the jointing stage of wheat growth, according to Shane Hand, product development manager for Osprey. Weeds should be from the one-leaf stage to two tillers in size.
“We will urge growers to get it out at the beginning of the season and reduce the amount of weed competition you can have in that field,” he said. “We've seen our best control when Osprey is applied early in the season to actively growing weeds.”
The Osprey label will have a range of rates from 3.2 ounces for weeds like wild oats that are more of a problem in the Pacific Northwest to 4.75 ounces for Italian ryegrass, a major concern for growers in the Mid-South.
“With later applications, when you have some type of stress on the plant — it's too hot, too dry or too wet — you may see a little yellowing and more stunting of the wheat,” Hand noted. “We recommend the applications be made in early December or before to remove early weed competition from the wheat.”
He said Osprey must be applied with a nonionic surfactant. Research indicates adding a nitrogen solution such as UAN or ammonium sulfate to the spray mix can improve control. Crop oil concentrates and organo-silicone materials appear to reduce the activity of Osprey.
In most of Scott's work with Osprey, the early application strategy has performed well, he said. “We have three or four good years of data where a single fall application of Osprey gave us control in the 90 percent range. 2004 was the worst we've seen for multiple flushes of ryegrass. We're continuing to research Osprey and will fine-tune our recommendations.”
Arkansas research has borne out Bayer CropScience's rates. “We believe they're right in their rate recommendations,” said Scott, who has worked with the compound for several years. “We've seen decreased control when we've conducted reduced rate studies with Osprey.”
Bayer CropScience strongly recommends that applications of Osprey be made in the fall and not delayed until spring, said Keith Vodrazka, technical service specialist with the company.
“The best application timing for control of ryegrass and for yield protection will be to apply Osprey to ryegrass that is one to two tillers in size, and that usually means a November or December application. When applications are made in the spring, weeds are too large to kill consistently and crop yields are reduced due to weed competition.”
The company will recommend the addition of ammonium sulfate at 1.5 to 3 pounds per acre or UAN at 1 to 3 quarts to the spray mix, he noted. “Our experience shows that using a good quality non-ionic surfactant 80-20 or above at one-half percent plus the recommended amount of nitrogen will work great.”