I have been taking part in a series of industry-sponsored meetings, talking to rice consultants about the need to rotate chemistries for barnyardgrass control in rice. Much of this comes on the heels of news that over 60 percent of the rice acres in Arkansas could be Clearfield rice next year. That means there will be a heavy reliance on Newpath for grass weed control in addition to red rice control.
Newpath has been a very good barnyardgrass control material in rice for the past five to six years. However, last year we discovered a population of barnyardgrass near Delaplane, Ark., that can tolerate ALS chemistry (ALS refers to aceto-lactate synthase, the enzyme inhibited by these types of herbicides).
ALS rice herbicides include Newpath, Regiment, Beyond, Grasp, Londax, Permit and Strada. This family is prone to the development of resistance. There is much concern that ALS-resistant barnyardgrass will develop rapidly with Clearfield rice and Newpath being used on so many acres.
In addition to ALS-resistant barnyardgrass, we currently have documented barnyardgrass that is resistant to Command, Facet and propanil.
Since barnyardgrass can readily cross-pollinate, it is not that hard to imagine a barnyardgrass population that none of the aforementioned products would kill. Just so we are clear, that would mean that of all of the rice herbicides available, only Prowl, Bolero, Clincher and RiceStar would still be effective.
While this would still leave us with a few tools for barnyardgrass control, these products can be difficult to build a true program approach around. For example, Prowl/Bolero would need to be applied delayed-pre only and the Accase-inhibitors (Clincher and RiceStar) have no residual and need excellent moisture conditions to work properly.
Now more than ever before it is important to understand which family of chemistry you are using for grass control in rice. The families are grouped by their modes of action. In the Arkansas Extension guide MP-44 we have organized the herbicide trade names and chemical names by mode of action. That actually may make it a bit harder for you to find the herbicide you are looking for. We hope to get you thinking about modes of action and whether or not you are rotating the chemistries on your farm.
I encourage you to develop a weed control strategy or program that involves at least two full rates of two different barnyardgrass herbicides on your farm. Weeds are much less likely to develop resistance if more than one herbicide with different modes of action are used each year.