pigweed in soybeans

Overlap residual herbicides to control pigweed

The key to a successful pigweed control program in the absence of switching to LibertyLink soybeans is to overlap residuals.

In soybeans, many of you already put down an early application of Valor or one of the Valor premixes; some made it to planting and put another residual down at planting. I like this program. I usually save fomesafen (Flexstar) for my post application, which also has some residual.

Another good option is Prefix (Dual + Flexstar) early post. On wider row crops a final shot may be needed. A product like Warrant or Zidua can fit in here. The bottom line is to try and never let the pigweed up.

In some areas of northeast Arkansas, rainfall has prevented this normal progression of layering residuals. Some have gotten no burndown out, others got one out but planting is delayed. I have talked to some growers about extending this residual with a second burndown plus a different residual. Many are opting for Dual, Fierce, or one of the Authority products.

(Click to open MP44)
(Click to open MP44)

Hopefully they can make it through planting and skip the pre- at planting if they do this and go with an early shot of Roundup plus a residual post. Many in this case will use Prefix.

Remember that row spacing may determine the number of treatments that you have to make in soybeans. The wider the row, the more residual shots you will need. I have said it before, but in my opinion we do not currently have the technology to grow Roundup Ready beans on 38-inch rows where resistant Palmer pigweed is present. I think you should either narrow your row spacing or switch to Liberty beans if you are going to stay on 38-inch rows.

For some growers the pigweed problem is so bad that LibertyLink is the only realistic option. Switching to LibertyLink soybeans, a residual just before or at planting can make a big difference. On wider rows I think you need at least two residuals and two Liberty applications to control pigweed season-long. I also like a program in Libertylink where we start real clean and come in with a very early post application of Liberty Plus Prefix. This works especially well on narrow row soybeans (15 inches or less).

Because of the time of year, LibertyLink has kind of become the product of choice for wheat-beans. I would still mix Dual, Warrant or Zidua or Prefix with the first post shot to try and get a second mode of action in there and get at least some residual control even though the wheat stubble will tie some of it up. There is a new generic form of glufosinate available, the active ingredient in Liberty — Cheetah, which is glufosinate alone, and Cheetah plus, which is glufosinate plus fomesafen (Reflex/Flexstar).

My soybean research is made possible by a grant from farmers in the state of Arkansas, through the Arkansas Soybean Promotion Board, and their support is greatly appreciated.

TAGS: Management
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