What is the best herbicide for corn that is being planted into fields with overwhelming Palmer amaranth soil seed bank? There are two key aspects to manage heavy GR Palmer infestations in corn. First is to use at least two herbicides with good activity on Palmer amaranth. The second is to use these herbicides in a split application.
The number one herbicide combination used on corn in Tennessee is atrazine and glyphosate. In 2008, Eric Prostko (et al.) at the University of Georgia confirmed atrazine and glyphosate resistance in the same Palmer amaranth plant. Utilizing a glyphosate and atrazine tank-mix on fields with a huge Palmer seed bank greatly increases the probability of finding a Palmer pigweed in our state resistant to both atrazine and glyphosate. We cannot afford for that to happen.
That is why we must use at least two modes of action effective on Palmer pigweed in corn. Fortunately there are many herbicides in corn that will control Palmer applied pre, post or both. Some of these include Dual Magnum, Frontier, Harness, Callisto, Laudis, Armezon, Impact, Status, 2,4-D, simazine and, of course, atrazine. Because there are so many herbicides that can be used in corn that can control Palmer amaranth it really matters more how they are applied than which herbicides are used. In general, the herbicides should be applied in some kind of split application. Some producers are not aware that traditional pre herbicides in corn like Bicep, Lexar, Harness Extra, Degree Extra, etc. can be applied post emergence in corn. They can be applied post and they provide better pigweed control applied in this fashion. A good method is to apply 1/3 of the labeled rate for the soil type pre emergence and then follow up early post emergence with the other 2/3 of the labeled rate. This typically provides the most consistent pigweed control. Moreover, the newer premixes that contain a bleacher herbicide like Halex GT and Capreno work very well post emergence in corn after atrazine, simazine or Verdict has been applied pre emergence. Be advised that the bleaching mode of action based herbicide premixes provide the best control on Palmer when atrazine is mixed with them.
Unfortunately, Palmer amaranth control does not end there even if weed control early in the corn growing season was successful. Corn can hide late emerging Palmer pigweed. Anywhere light can hit the ground expect Palmer to emerge once the herbicide has played out. In areas where the corn is thin Palmer can emerge as early as June and will grow 6‘ tall and produce a lot of seed. Later as the corn is drying down Palmer amaranth will emerge well into September or later and even small Palmer can produce some seed. Therefore weed control must be maintained even after corn harvest. This can be accomplished with tillage or a herbicide. Regardless of how it is done the only way to reduce the soil seed bank is to minimize the Palmer pigweed seed production throughout the entire year.
Don’t forget VERDICT!
Greg
You make a good point. We do need to use all the tools available to manage herbicide resistance now and in the future. Verdict would be a good fit in a pre followed by post system.
Larry
And Don’t forget the New POST herbicide just introduced by BASF, ARMEZON!!!
Greg
I wrote this article before Aremzon was annouced. I will write a more comprehensive article on the bleaching herbicides in a couple weeks. Between the introduction of Aremzon and resistance being confirmed in IL, IA and NE to HPPD herbicides an extensive artile is warranted on this topic.
Larry
Great article for corn. Any plans to write the same article but for cotton and soybean fields with heavy Palmer pressure? Thanks.
Tom
Thanks for the comment. Soybean and cotton planted into fields with heavy Palmer pressure will be addressed in future articles. Many of these fields will go to Liberty Link cotton and soybeans. Then right out of the gate we will be putting severe selection pressure on Liberty herbicide. This definitly warrants several articles.
Larry
Larry,
When you get to the articles on Soybeans, do not leave out suggested programs for conventional beans. There are quite a few people I’ve been talking to, that are looking at going back to conventional bean varieties, vs. just switching bandwagons to Liberty. If the bandwagon switch is done, I really expect to find ourselves back in the same shape we are now, and expect it to take less time to get there. Personally, we have committed to going 100% conventional beans. I’m needing to use Select for Johnsongrass, Italian Ryegrass control anyhow, so there is no use having R-up in the mix or paying a tech fee for the R-up beans.
Chris
Thanks for the imput. In many ways a RR soybean program has to be managed as a conventional program for fields infested with GR Palmer and goosegrass. I agree we do not need to go all in on any one technology. The only way to make weed control sustainable is for folks to rotate their herbicide program between years or even between fields. There are very few soybean growers who plant all one variety. They plant several different varieties to spread their risk. The same really should apply to weed control for combating herbicide resistance.
Larry
Larry,
Will burning a field that has a significant amount of crop residue plus a heavy resistant pigweed seed bank help in managing the pigweed in the next crop? I have fields that have been in continuous no-till for many years that have choking pigweed pressure and I am wondering if the heat from burning-off the field would kill the germ in the seed from the resistant pigweed.
Richard
Good question…. We definitly need to think outside of the norm in order to long-term control this weed. Unfortunatly, fire will not destroy pigweed seed. In fact it may help the germination of the Palmer seed. During my Ph.D research I soaked pigweed seed in concentrated sulfuric acid and improved the germ by 70%.
Thanks for the question,
Larry