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Palmer pigweed: residual herbicides

In last week’s article I wrote that planting LibertyLink soybeans and using Ignite herbicide provide the best opportunity to consistently control glyphosate-resistance Palmer pigweed.

Ignite has the best postemergence activity of the available herbicides and, therefore, provides the best backup for a residual herbicide program.

Whether you choose conventional, Roundup Ready or LibertyLink soybeans, I recommend a residual herbicide program. Perhaps it does not need to be as aggressive in LibertyLink soybeans, but some use of residuals is recommended.

With any of these programs you have to be prepared to deal with the weeds that escape the residual treatments. We have a lot more years in Arkansas where timely rains for activation do not occur than we have wet years like 2009. You must be prepared to deal with anything from a total failure of the residual to anything less than 100 percent control (and you will get very few 100s).

In a conventional weed control program or a Roundup Ready program depending upon conventional herbicides to control the resistant weeds, Flexstar and Blazer are the two primary postemergence options. With either, they must be applied to very small weeds and there is a point at around 14 days after emergence they simply will not work anymore.

In addition, even when they work well it is easy to get 80 percent control with them but very difficult to get 100 percent control.

One of the things we have going for us right now is the resistant populations in a lot of fields are at a low enough level that 80 percent control of any escapes following a residual treatment looks pretty good.

If we continue down the same road we are on, in a couple more years we will have the pre–Roundup Ready high population of the 1980s, except they will all be glyphosate-resistant. What would happen in the 1980’s and early 1990’s (the problem Roundup Ready solved until now) is the residual treatment would give partial control, the Blazer and Flexstar type treatments would give 80 or even 90 percent control of the escapes, if everything was done right, but the end result still was a grown up mess.

I attempt to write at least once in most articles that we still have the opportunity to head off the worst of the problems in a lot of fields if you will just change your program now.

Changing the program can be through better use of rotation crops such as corn, better use of conventional herbicides in a Roundup Ready program, the use of LibertyLink soybeans or a combination. University research the past two years has shown that Ignite herbicide in LibertyLink soybeans has the best postemergence activity on glyphosate-resistant pigweeds.

In addition, my experience with the technology in the field the past two years has shown that LibertyLink soybeans provide an excellent pigweed control option. Ignite has better activity on resistant pigweed than the commercial standards and it also represents a new herbicide mode of action for resistance prevention and management.

I wrote in last week’s article that the key to controlling pigweed and also grasses with Ignite would be learning how to use Ignite like Ignite and not trying to use it like glyphosate.

I like Ignite best in a program with residual herbicides because the program is more consistent plus the residuals provide alternative modes of action for resistance management with Ignite. Two timely applications of Ignite have provided excellent pigweed control when applied in systems where the soybean canopy closes quickly.

As a result, the LibertyLink system is not as dependent upon residuals as a conventional or Roundup Ready program on resistant pigweeds. However, a program using some early preplant, pre-emergence or residual tank mix partner with Ignite is by far the best choice.

Next week I will get specific on how to make these programs work.


TAGS: Soybean
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