Last year we observed an increase in the number of fields with ryegrass that was resistant to Axial XL herbicide, a slightly different ACCase inhibitor from Hoelon which we have been relying on for some time.
For the past three years now we have recommended Anthem Flex or Zidua delayed pre or Axiom plus Prowl H2O or Anthem Flex/Zidua early post in the fall followed by Axial XL in the spring for ryegrass. This is mainly due to resistance levels to Hoelon and the ALS chemistry being high in Arkansas ryegrass populations.
These Axial XL-resistant fields make me wonder if we could be heading to a point where we cannot grow wheat in Arkansas due to herbicide resistance.
Our Axiom/Prowl H2O followed by Axial XL program allowed many growers to “get by” for one more season. I will not say it was perfect, but we grew a wheat crop instead of a ryegrass crop.
I also know that there were a number of failures where only ALS herbicides were used in 2013-14, so the problem is still there.
In 2014-15 Anthem Flex and Zidua helped some, but not being able to use them pre-emergence to the wheat has greatly limited their potential. We did find that a late fall treatment of Athem Flex or Zidua plus Axial XL was as close to a one-shot ryegrass program in wheat that I have ever looked at since Finesse (prior to ALS resistance).
In our research programs, we feel that we have exhausted our options with what we can do for ryegrass chemically. Although I know some of you have tested Zidua as a pre, we and the companies saw too much injury from time to time and no one was willing to accept the risk of labeling it that way.
There does appear to be varietal differences, but that could be due to emergence as much as genetics and has been impossible — at least for me — to successfully quantify.
Therefore, we are conducting a screen of many of the new rice herbicides and other herbicides not currently labeled for wheat to see if there is something out there that has been overlooked that might have potential as a ryegrass herbicide for wheat.
As always, we continue to look for novel ways of controlling ryegrass in wheat. One new project we have is looking at post-harvest destruction of ryegrass seed. Right now this will involve windrow burning but may evolve into seed destruction devices in the future.
My wheat work is funded by the Arkansas Wheat Promotion Board and without their support it would not be possible.