Cotton Seed Distributors - Web on Wednesday

Prof. Rick Roush - University of California, Davis Campus - Discusses the potential of Glyphosate resistance in the cotton industry.

Rick, the possibility of Glyphosate resistance, we have populations of annual rye grass in southern Australia, what are the key areas of concern there?

It was always thought that resistance couldn’t evolve at all to glyphosate let us say Roundup® and related products. What we have realized since is that it is very hard for weeds to evolve resistance to glyphosate but not impossible.

So then on a steady exposure to glyphosate alone as a primary control tactic for fifteen or twenty years you can get resistance, we have seen it with a weed in Malaysia, with annual rye grass in California, with annual rye grass in Southern Australia and in particular a wide spread weed in soybean growing areas in the United States, Conyza. So if you hammer the populations year after year you can get resistance and particular in the case of Conyza it was a case where the weed was probably not very sensitive to roundup anyhow.

The very modest levels of resistance that we get in roundup resistance plants the very modest levels of resistance we get are enough that actually start to make these weeds problematic for control. It is not a big deal with most kinds of herbicides like Triazenes or ALS inhibiting herbicides you get resistance and you can’t control the weeds at all. Glyphosate is not like that the levels of resistance are quiet low so it is one of those things that really become a problem but not a crisis.

What I wanted to try and argue today is that with relatively little effort people could stay on top of this problem and prevent it from ever getting there, and I should add its really something that probably you know what some one does on their individual farm, in contrast to heliothis which will move all over the place, if you don’t manage weeds properly the weed problems and resistance problems are going to be your own.

It is really up to the individual to do this. The kind of things that people are encouraging like staying on top of the weed problems if there are very many survivors going out and doing something about it those are the important. Certainly what we have found in Adelaide is that there seems to be very high fitness costs that if you just don’t use roundup year after year the chances of resistance evolving are much lower.

For a lot of weeds in cotton and other crops rotating herbicide practices are a good idea because some weeds are intrinsically less susceptible to roundup any how so just from the stand point of trying to avoid weed spectrum shifts, it would be a good thing to keep switching things. So the motto in herbicide resistance with all due respect to John Laws is when on a good thing don’t stick to it - keep shifting ground on the weeds, rogue them out, change the herbicide practice every now and then just to keep them off balance and we can forestall this problem so it never really becomes an issue.

And tillage would become an important part of that process?

Tillage can definitely be an important part of the control process because you can control at least some of the surviving weeds that might have appeared in the rows after treatment. So tillage is important and any kind of control tactic that helps keep the weed densities under control can be very useful.

Further Information:  Robert Eveleigh, John Marshall,  Craig McDonald or David Kelly