Until new weed control traits arrive, the backbone of weed control programs for Palmer amaranth will be glufosinate, PPO herbicides and continued use of "out of the box" approaches.
Though we do have more grown-up, messy Palmer amaranth fields than last year, it is apparent that overall weed control this season is better than I thought it would be, given all the issues this spring. The main issue was the lack of time to spray pre-applied herbicides or in some cases post-applied herbicides due to the weather.
This problem is even more of an issue this year as it seems everyone is planting with one of the big air seeders that can plant a tremendous amount of acres in a short period of time. These new, big and fast planters essentially compress the time window that a large amount of acres will need to be sprayed and, in essence, can make it impossible for the sprayer to keep pace even in a very forgiving spring.
From a weed control standpoint, we still have a lot of fields that have some Palmer amaranth in them, but not that many are at drastic, yield-reducing levels. Even fewer had to be disked down and replanted due to Palmer amaranth infestation than I thought would be the case. The few fields that were replanted were mostly in middle Tennessee.
I know that relatively clean fields were not achieved easily. They were much more costly in time, equipment, labor and above all money than when glyphosate would control Palmer amaranth at any height.
One of the reasons that cotton and soybean fields look better than I expected is that more folks seem to be aware of post-harvest weed control last fall, which reduced the amount of Palmer amaranth seed produced after corn harvest. This reduced the number of Palmer amaranth that had to be managed this spring in cotton and soybean. Moreover, more farmers utilized cover crops last fall with a considerable amount of it sown with an airplane into a standing crop.
We had perfect weather last fall for this to work as most stands of the cover crops were quite good. For the most part, the covers helped provide control of horseweed (marestail) and suppressed some Palmer amaranth early on this spring. Finally there seemed to be more chopping crews out in 2014 than I can recall in past years. In part I think the cool weather this summer made it easier to chop Palmer amaranth out of cotton and soybeans. Many growers have hired chopping crews, and those who didn’t are stopping the truck and going out and hand pulling a few escapes in a field. All of these out of the box weed control approaches often helped supplement the herbicides when they could not be applied timely.
Looking ahead to next year, I know many farmers are expecting Dow’s Enlist trait and Monsanto’s Xtend trait to be available for help on Palmer amaranth. In soybeans, it will be some time before we see these technologies available for planting as approvals overseas, particularly China, are moving slow.
My understanding is that the new soybean herbicide-tolerant trait technologies, at best, will be two if not three years away before any significant acres are available to plant. Even then, these new herbicide-tolerant traits work best if cultural practices and some other herbicides are used with them. They are much less consistent and will not last long if dicamba with Xtend or 2,4-D with Enlist are all that is utilized to control Palmer amaranth.
In cotton, we very well may have the new herbicide-tolerant traits in some supply a year or so earlier than soybean. Again, a complete weed management system will need to be employed to obtain consistent control with those technologies in cotton.
In short, glufosinate and the PPO herbicides will continue to be the backbone of Palmer amaranth management for at least the next two to three years. My hope is that Palmer amaranth does not develop resistance to these herbicides before the new traits come on line in significant quantities. A good way to make that a reality is to continue to utilize some of the out of the box approaches to weed control many of you have started to embrace. That way when these new herbicide traits arrive in some volume, we may have enough herbicide diversity to be able to manage Palmer amaranth long-term.