Ryegrass control will become more difficult

Bob Scott had an excellent article on ryegrass control in wheat in the Sept. 19 issue of Delta Farm Press. The point was made that most of the ryegrass in Arkansas can be considered resistant to Hoelon. This has shifted the effective ryegrass control chemistry to the ALS inhibiting herbicides such as Finesse, Osprey and PowerFlex.

Since that article was written we have received a report back after my wife, Tomilea, sent ryegrass samples from five wheat fields to be tested at the University of Arkansas for herbicide resistance. The ryegrass seed were harvested from wheat fields where control failures with Osprey herbicide had occurred in both central and northeast Arkansas.

The ryegrass seed were grown out at the University and sprayed with Opsrey, Hoelon, Raptor or Beyond (that would be used in Clearfield wheat) and PowerFlex. Hoelon is an ACC-ASE inhibiting herbicide and the others are ALS inhibitors.

The ryegrass from all five fields survived at least a 1X rate of all four herbicides with most surviving 2X to 4X rates in the testing. The ryegrass from one field tested resistant to all four herbicides at 4X rates.

There is no way the above information can be considered good news. If there is any positive spin to put on the data it is the samples were all pulled from suspect fields as opposed to samples being pulled at random.

However, if previous experiences with ALS resistance hold true, you can expect the resistance to spread rapidly and the effectiveness of the ALS inhibiting herbicides for ryegrass control in wheat to diminish quickly.

This does not come as a total surprise. When ryegrass in Australia developed resistance to Hoelon, it was resistant to the ALS inhibiting herbicides almost immediately.

The information presented here should not be interpreted to mean we are out of business overnight. However, since our most effective ryegrass herbicides have been either ACC-ASE or ALS inhibitors, I believe the results do indicate that ryegrass control in wheat is going to become much more challenging.

It appears at this point that wheat acres in Arkansas will be down dramatically this fall. If you have fields where wheat is traditionally grown and ryegrass is a problem, and you do not plant them this fall, you have an excellent opportunity for a fallow program.

We are going to have to look beyond herbicides for some of our ryegrass control. I have never forgotten a comment Steve Powels from Australia made to me years ago. He said, “Herbicide-resistant ryegrass changed me from a herbicide scientist to a weed scientist.” What he meant was all of the answers to our weed problems do not lie in herbicides.

This has been a very trying, expensive and difficult crop year. The last thing you likely want to do is go work up fields that will not be planted in order to destroy a bunch of ryegrass. However, research at the University of Arkansas has shown that one year of fallow can effectively reduce a severe ryegrass population to one that does not require a herbicide application for ryegrass the year after the fallow.

The key to the effective fallow is preparing a good early fall seedbed and then tilling and destroying the ryegrass seedlings as they emerge.

While some disagree or do not like it, I believe strongly there is another message here — the weeds are simply catching up with our current herbicide technology.

Some consumers continue to oppose the development of genetically modified crops, especially primary food crops. However, as the weeds demand new technology, weed control must come in the form of new and novel herbicide chemistry or in the form of traits that allow us to use herbicides we already have.

It is obvious to me that technology change in the foreseeable future is going to be in traits. If we cannot make some breakthroughs in consumer acceptance, weed control is going to get increasingly difficult in some crops in a hurry.

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