Time for weed control in wheat

I prefer to control ryegrass in wheat in late fall if possible, because most weed competition occurs when wheat and ryegrass are small. The longer that ryegrass control efforts are pushed back into the spring, typically the more yield loss you can expect.

Additional fertilizer may or may not overcome this loss. So, in general it is a good idea to control ryegrass in wheat early.

Also, if you are using Hoelon, University of Arkansas data suggest that lower rates can be effective on ryegrass prior to tillering. If you wait until after ryegrass has reached the two- to three-tiller stage, the full rate of 2.67 pints per acre of Hoelon is required.

Due to factors such as weather, late-germinating ryegrass and hunting season, wheat does not always get the attention that it deserves in the fall. Many fields are in need of ryegrass control treatments this spring in Arkansas.

In addition to Hoelon, Osprey herbicide can be used for spring ryegrass control in wheat. Due to the reduced number of wheat acres last year, this is really the first full season of use for Osprey. The following are some general comments and recommendations on using Osprey herbicide in wheat.

Performance of Osprey on larger ryegrass (two- to three-tiller) has been excellent in our plot work over the past few years. Where we have sprayed ryegrass in the spring we have had good results.

Also, Osprey has been effective at controlling Hoelon-resistant ryegrass at our resistant location. It has several other advantages over Hoelon later in the season: Osprey is cheaper and it has activity also on annual bluegrass, chickweed, henbit, and vetch (not on the current label).

In addition, where you have both ryegrass and wild garlic/onion, Osprey can be tank-mixed with Harmony Extra or Peak. Peak has a nine-month rotational interval to soybeans, while soybeans can be planted double-crop following Osprey and Harmony Extra. Osprey has a 12-month rotational interval to corn. Most other Southern crops are 90 days.

Osprey can be tank-mixed with most broadleaf herbicides in wheat except for 2,4-D, Clarity (dicamba), and Sencor. These tank mixes may result in antagonism of ryegrass control.

Osprey herbicide has only one use rate (4.75 ounces of product per acre) and you must add 1 to 1.5 pints per acre of methylated seed oil (MSO) to the spray solution. An alternative to the MSO is to add 0.5 percent nonionic surfactant plus a spray grade ammonium sulfate (AMS). In our research these spray additives have improved consistency and speed of activity of Osprey.

If you are planning to apply nitrogen to your wheat this spring (top-dressing), avoid making an Osprey application too close to nitrogen fertilization. The most current label that I could find called for 21 days between fertilization and herbicide application. However, it is my understanding that you can actually safely apply Osprey as early as 14 days before fertilizer application, or 14 days after the fertilizer has been activated by rainfall.

Osprey was used in Arkansas in several fields last year with no injury reported and we have not observed injury in any of our treatments over the past three to four years.

At times Osprey activity can be very slow. So far this year, performance has been reported as good for the most part out in the field, but some consultants get nervous waiting on it to work. Under good conditions it can take up to four to six weeks before you can really tell if Osprey is working or not. When temperatures fall below 50 degrees after application, activity can be even slower.

In addition Osprey should not be applied when ryegrass is under moisture stress. Osprey offers no residual activity on ryegrass and good spray coverage is essential.

Bob Scott is the University of Arkansas Extension weed specialist. e-mail: [email protected]

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