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Agribusiness: Applying new herbicide to help control ryegrass

Due to heavy rains, low price and high input costs, wheat acres were significantly down across Arkansas and much of the South last year. For many, the price of diesel and fertilizer may limit wheat acres again this year.

This has made for a slow launch of Osprey, the new Bayer herbicide for wheat. Prior to last year, Hoelon-resistant ryegrass acres had been on a steady increase in Arkansas for the past decade or so. However, with the decline in wheat acres, the incidence of new fields with resistance has also declined.

If you are one of the many who will not be growing any wheat this year, I strongly suggest taking this opportunity to get rid of as many flushes of ryegrass as you can germinate on your fallow wheat ground. It is important to remember that glyphosate is generally very good on ryegrass from emergence through about 2-4 tillers in the fall. However, once it goes reproductive in the spring and gets some size on it, it can get hard to kill.

Keep a late-fall application of glyphosate in mind for your fallow wheat ground. For that matter, you may want to consider this or at the very least an extremely early spring burndown for ryegrass on all your acres with ryegrass. If ryegrass gets too big for glyphosate your next best option is probably tillage.

At my Hoelon-resistant ryegrass location, it often takes two applications of glyphosate for season-long control of ryegrass in the fallow areas. This may be the case on some farms as well. However, keep in mind that most ryegrass seed germinates in the first season after it is produced. Just one year of fallow can result in as much as 90 percent ryegrass control in the following crop.

For those of you who are growing wheat and have Hoelon-resistant ryegrass, this may be a good time to consider trying the new product Osprey. 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. The Osprey label includes a lower rate for wild oat control; however, in our work, 4.75 ounces were needed for consistent control of ryegrass.

In addition to ryegrass, Osprey will suppress or control many broadleaf weeds, including vetch, shepherdspurse, mustards, henbit and buttercup. It is an excellent wild oat material. 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. Osprey should be applied in the fall to actively growing ryegrass somewhere between the four-leaf and two-tiller growth stage. Early control of ryegrass is essential to maintain maximum wheat yields. However, Osprey has no residual activity, so a single well-timed postemergence application is needed.

In circumstances where a fall application is missed, however, it will be possible to apply Osprey until just prior to wheat jointing. So, salvage ryegrass applications are labeled, but I recommend you get it under control before then.

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. However, Harmony Extra, Express, Finesse and others are approved. We have observed no antagonism in our trials over the past three 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.

Finesse herbicide has been an option in Arkansas for Hoelon-resistant ryegrass control; however rotational crops are serious concerns. 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. One option on Hoelon-resistant acres would be to use Finesse and see if you get a rain before you invest in Osprey.

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

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