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Managing barnyardgrass begins in soybeans

It is much easier to talk about potential problems with barnyardgrass resistance in rice than it is to talk about solutions. Small things that can be done with existing technology can help, but there is the need for new technology.

One thing that can be done with existing technology that would help the most is to do a much better job of controlling barnyardgrass in soybeans.

Riding the roads each summer I see two disturbing scenarios.

One is the increasing failure to control barnyardgrass in Roundup Ready soybeans. Much of this is due to later timing of application and the attempt to get by with one application. If the experts — who contend that glyphosate resistance is a “creeping resistance” that builds up over time — are right, then applying sub-lethal doses will result in resistance over time.

Continues to increase the cost of this technology each year could be a counter-productive resistance management program because it will cause more farmers to reduce the amount of glyphosate applied when they really need to be increasing the amount used.

Another barnyardgrass scenario I see increasing in soybeans is where excellent early control is achieved but a follow-up application (or applications) is not made. The result is a level of control that protects the soybean yield but allows a big flush of barnyardgrass to emerge late and go to seed after soybean leaf drop.

The end result of both scenarios is a tremendous increase in barnyardgrass seed in the soil seed bank. When you combine the increase in the soil seed bank with an increasing difficulty in controlling barnyardgrass with our existing herbicides, you get a double whammy that can simply overpower anything you try to do for control in the rice crop.

There are a lot of things you can do in the soybean crop to help. If the current glyphosate program is not getting it done, then adjusting timing, rate and number of applications is an obvious first option.

Another option is the use of a good residual grass herbicide. I would argue that the use of residuals in a Roundup Ready program has become just as important as they are going to be in a Liberty Link program. If a farmer is not going to make the timely, repeated applications I believe it takes to make Roundup Ready programs effective, getting a grass residual herbicide out up front will help a lot.

It will also get some diversity into the program to help some on resistance management.

We still have available good postemergence grass herbicides such as Select and Assure. If glyphosate alone is not getting it done, there are options to supplement the program with one of these. After all, we used to get excellent grass control with a residual herbicide and the postemergence grass herbicides in the days before Roundup Ready.

In the Liberty Link fields I observed this year, I was pleasantly surprised by how good the barnyardgrass activity was. Barnyardgrass is not a weed I would consider a real strong suit for the Liberty Link/Ignite technology. However, it was very obvious this year that using a residual grass herbicide followed by two timely applications of Ignite made an excellent barnyardgrass program.

I had no intentions of using the entire article on this topic. One reader who recently e-mailed made a comment along the lines of “you encourage us when we need encouraging and scold us when we need scolding.” My intent is always to encourage and never to scold.

However, the fundamentals of managing barnyardgrass resistance must begin in the soybean crop. The goal should be to achieve 100 percent control. There is plenty of capability to do that in a Roundup Ready program, in a conventional program, or a Liberty Link program.

Total control in the soybean crop is important for rotating to herbicides to control barnyardgrass that can not be used in rice and also to drastically reduce the soil seed bank to make control in rice easier to achieve.

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