There are six confirmed glyphosate resistant weeds in Arkansas now. In soybeans and cotton, two of the weeds, Palmer amaranth (pigweed) and horseweed, have pushed the options that we have for control to the limit.
A lot has been made of the introduction of Ignite herbicide and LibertyLink cotton and soybeans this year and for good reason. Ignite gives us a new tool for controlling pigweed in these crops. New tools have been few and far between for the past several years.
The newest mode of action in herbicides is the HPPD inhibitors. This class of chemistry is over 25 years old! We do not use many of these in Arkansas.
Callisto may be the most common to many of you. Many have hailed Callisto as the next best thing to atrazine. In corn production areas it is a good replacement for atrazine if you cannot use atrazine for some reason. The last time I checked, it cost more than atrazine.
A couple of recent articles in the Delta Farm Press got me thinking about herbicide options. The first was an article about the announcement that tall waterhemp (a relative of Palmer amaranth) resistant to HPPD inhibitors was found in the Midwest. The second article was about the EPA’s current focus on the registration status of atrazine and re-registration of atrazine.
The lack of new herbicide registration in cotton and soybean, the lack of new herbicide development in general, the increasing occurrence of resistant weeds, and the feeling that we are losing more products than we are getting approved at EPA have me concerned that we are headed for a train wreck.
We have little control over the development of herbicides and the potential discovery of new modes of action. From where I sit, the basic manufacturers seem to have more interest in herbicide development. If, however, we found a new mode of action, under our current labeling timeline we are probably looking at a minimum of seven years to develop before we could get it to the farmer. This means we have to survive on our current chemistry until new active ingredients are discovered and eventually make it to market.
One thing that we can control is what we do with existing technology. I do not believe at this time we can afford to lose atrazine. I do not mean that from an economical standpoint to the grower, although that is and should be a consideration. We cannot lose it, because it works on four of the six glyphosate-resistant weeds that we have.
No, you cannot use atrazine in cotton or soybean, but you do rotate both crops with corn. I believe that good crop rotation has played a big role in preventing a more rapid development of glyphosate-resistant weeds in the Midwest.
Crop rotation and herbicide rotation are major ways we can save glyphosate and Ignite. I usually do not get that involved in policy, but this has to be considered by those in positions to make decisions about cutting a herbicide. We simply cannot lose any tools at this time. Atrazine is a very important tool right now!
We are faced with a similar situation in Arkansas in our rice/soybean rotation acres. This segment has been slow to develop glyphosate-resistant weeds. This is at least partially due to the fact that rice is flooded and neither horseweed nor pigweed can survive a flood. However, recently we have seen a major increase in the occurrence of glyphosate-resistant Palmer amaranth on rice levees. I believe this is due in part to a recent ban on the use of 2,4-D in many counties after April 15, well before time to spray rice levees. None of the current rice herbicides will control pigweed as well as 2,4-D.
The ban on 2,4-D by all accounts has been a success. Very little late phenoxy injury is being reported on cotton in these counties. I believe that the next step should be to examine what uses we can now allow without changing the success of the program. One of these is the use of small ground rigs to apply 2,4-D late on rice levees for pigweed.
Policymakers are in a position to determine the success or failure of some of our resistance management efforts. I encourage you to let them know your position. Hopefully, they will consider these fundamental issues along with other factors that affect labeling and use restrictions. When options are so limited, the loss of just one can result in a breakdown in the system.
The system is currently broken or at least breaking down in cotton, and soybeans are close behind. We are hoeing more fields than in the last 15 years and I had to buy a wiper wick bar rig the other day to look at some salvage options in cotton, peanuts and soybeans. At this time, we cannot afford to lose any herbicides that control pigweed.
e-mail: bscott@uaex.edu