Curtis Thompson Kansas Corn School

(Curtis) Curtis Thompson, Extension Weed Scientist for Kansas State University and I was here today visiting with the corn growers regarding the weed management issues that they are dealing with. And the title of my presentation was actually, “Weed Management May Become Increasingly Difficult.” And of course as we look at how weed control programs have changed over the years we were in a period from the late ’90s and into 2000 when glyphosate was the base and everything was working extremely well. We were in a honeymoon period. And basically today what we talked to the growers about is perhaps the honeymoon is over. We’ve had a number of different resistant weeds pop up. We spent today focusing on two of the pig weeds, palmer amaranth as well as water hemp. Both of those having developed resistance to ALS inhibitors, to glyphosate, to the triazines. We have PPO resistance to the water hemp and we have HPPD resistance to the palmer amaranth in Kansas and also to water hemp in other states. And so we know that the potential to HPPD resistant water hemp does exist here within the state of Kansas. And what we did is we walked through a number of potential ways in which we can manage some of the various weed populations that have these different resistances. We did spend some time in our new 2015 Chemical Weed Control Guide, that should be available in the county agent’s offices here. But one of the real concerns that does hit me is one of the last resistances we’ve come up with is the HPPD resistant. This group of herbicides have been the primary way in which we are dealing with the glyphosate resistant pig weeds. And so if we have resistance to this HPPD herbicide that does hurt us significantly as we look at the two populations in Kansas one in Russell County, one in Stafford County. We find that they are also resistant to the triazines like Atrazine and Metribuzin. They are also resistant to our ALS inhibitors and there’s a whole host of ALS inhibitors and so we run out of things fairly quickly. At this point we’re still controlling ’em with glyphosate, but the rate at which glyphosate resistance is spreading in pig weed, it’s only a matter of time and and we will have palmer amaranth populations resistant to the glyphosate, to HPPD to ALS and the triazines. What’s concerning about this HPPD resistance is that it is metabolism based. The Atrazine resistance in these populations is also metabolism based. That is new. Both of those resistances are transferred through pollen. And that means that pollen from pigweed can get up and move from one area to the next and infest susceptible populations, so it’s at great risk of seeing this particular resistance spread. And so I guess that kind of goes back to my title and managing or weed control in corn may become increasingly difficult. I still think it can be done, but it does require growers to be very timely, use pre’s followed by post programs. We may have to be more selective on the herbicides that we use, but I think in the end we’ll be able to handle these populations.

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