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Pigweed in conventional soybeans

I continue to receive e-mails about the articles on pigweeds and that is encouraging. That tells me I am writing about a topic of interest, but it also tells me that pigweed resistance finally has hit home to a lot of folks.

Hopefully we can now move forward and turn the problem around.

Most of the e-mails I have received have been from outside Arkansas, which tells me I am writing about more than a localized problem. The next several articles will be about my experiences, ideas and opinions about the control options available. In these articles, control options in conventional soybeans, Roundup Ready soybeans and LibertyLink soybeans will be discussed.

A logical starting place is to discuss control in conventional soybeans for a couple of reasons. First, there is a lot of history on Palmer pigweed control in conventional soybeans prior to the introduction of the Roundup Ready technology.

The other reason is I have heard a lot of comments along the line of “if I am going to have to use conventional herbicides in a Roundup Ready or LibertyLink program, I may as well save the upfront cost for those technologies and just grow conventional soybeans.”

The use of conventional herbicides in Roundup Ready and LibertyLink soybeans will be discussed in future articles. However, I would suggest considering a lot of things before you move to conventional soybeans for that reason.

I believe there is a place for conventional soybeans, but it may not be for Palmer pigweed control — at least not in dense infestations. That was one of the weeds that we were not able to control with conventional herbicide programs before Roundup Ready.

With that said, let’s look at a typical conventional herbicide program. A Palmer pigweed control program in conventional soybeans is extremely dependent upon getting excellent activity from soil residual herbicides. This was a great year for residual herbicide activity because of abundant moisture.

By nature, however, residual herbicides are inconsistent due to our erratic rainfall patterns most years. I could never get consistent pre-emergence herbicide activity on pigweeds in research plots in the years prior to Roundup Ready and growers’ experiences were similar.

Back then, almost everything was planted using conventional tillage and a lot of herbicides were incorporated. I am getting a lot of questions about that, and there may be a place for some incorporation. However, we have made great strides in conservation tillage and going back to incorporated herbicides will be counterproductive to that.

In addition, most of the incorporated treatments did not work very well on pigweeds either.

With most soybeans now being planted using conservation tillage methods, there are some options for getting residual herbicides to work that we did not look at in the 1980s.

First, we did not have Valor then or had not figured out how to use it. It probably has the best overall pigweed activity of any of the residual treatments. The university researchers now are doing a lot of work with Valor (and the numerous package mixes that contain Valor) applied in a burndown mix a couple of weeks prior to planting.

I like this concept for a couple of reasons. The biggest hurdle with a surface-applied herbicide is getting it activated. If you apply it at planting and it does not rain in three to five days, you have a flush of pigweeds up.

However, if you apply it around 14 days prior to planting, that is that much time to get it activated before you plant.

The other reason I like Valor applied prior to planting is it reduces the risk of injury. A lot of folks recommend and use Valor-containing products at planting. However, I do not recommend them at planting due to the risk of injury if you get a rain on them near soybean emergence. That is a personal choice as I feel the preplant application is a much better option.

I will start back here on control in conventional soybeans next week.


TAGS: Soybean
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