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Liberty, pigweed lessons learned in 2012

Liberty, pigweed lessons learned in 2012

I, like many of you, have watched as pigweeds have slowly re-infested many soybean fields that started off clean this year. I have talked to many growers who have spent a small fortune fighting Palmer amaranth this year only to see many fields still grown up.

There is little money left for hoe crews and no chemical options remain. Many of these fields will be combined, surely spreading the weed — not only in these fields but in others that the combine goes into later. I do not blame you for cutting these beans; there is money out there. Most fields are clean enough and were clean enough long enough that yield may not even be affected.

However, there will be plenty of pigweed left for next year to deal with. I’ll give you some thoughts about what we learned this year and a few suggestions for next year.

My first observation in the pigweed fight is that wide rows simply do not work. Whether you are staying in Roundup Ready or going LibertyLink, failure of the soybeans to canopy means that pigweed will continue to germinate all year long. I know that this may mean that you have to change the way you farm, but you must do what you can to narrow your row spacing.

People have asked about post applications of residuals like Dual and about hoods. Dual is a good idea and can help. There isn’t much else to pick from in terms of post residual herbicides for soybean because most of our pigweed are ALS-resistant. So products like Scepter and Classic don’t help much. As far as hoods go, it’s a good theory, but I am not sure what to tell you to put in one.

In side-by-side studies this year, our drilled soybeans were on average 10 to 20 percent cleaner at canopy than wide rows with similar or exactly the same herbicide programs. Drilled rows are best, if you must stay on beds. I would consider trying to get two or three rows per bed instead of one.


Variety selection may also be important, a more bushy-type bean versus an erect plant will canopy faster.

Next, if you have glyphosate-resistant pigweed, consider rotating to rice, corn or grain sorghum for a year and using products for those crops to fight pigweed. It is important to adopt a “Zero Tolerance” policy in your rotational crop. You just have to decide that you are going to do whatever it takes to not let pigweed go to seed on levees, turn-rows, post-harvest, etc. This can be a very effective tool at cleaning up a field.

If you must grow soybeans, consider switching to LibertyLink soybeans. We have over a half million acres of LibertyLink soybeans this year in Arkansas and they look pretty good. In our research, there has been no yield lag with these varieties. I know many of you have struggled with this technology. Here are a few things to consider for next year.

Plant narrow rows. Be sure to start clean (do not plant a field that has large pigweed already in it) and use a good residual at planting. I like the pre-mixes that contain two different modes of action against pigweed, such as Prefix, Boundry, Authority MTZ, Valor XLT,  and Envive (there are others).

Apply your first 29 ounces of Liberty when pigweeds are 2 inches tall. This is where most people go wrong. In our research, timing is about five times as important as rate. You cannot overcome a late Liberty timing by increasing the rate.

At this point, you still have Flexstar (as long as you did not use Prefix as your pre) and another shot of Liberty. If your Liberty is going out on larger pigweed, it is better to spray 29 ounces twice about seven to 10 days apart than to use higher rates. You can also tank-mix Dual or Prefix with Liberty for overlapping longer residual control.

At our location in Newport, Ark., we have a dense population of Palmer amaranth. We can put out Treflan or Prowl ppi, followed by Scepter pre, followed by Roundup + Classic or Synchrony and get about 40 percent control of pigweed.

With this kind of pressure and resistance we can still grow both Roundup Ready and LibertyLink plots that are nearly 100 percent control. Yes, we turn the pivot on and irrigate in our pre treatments, but we also do it with total post programs by hitting our timings just right and using drilled soybeans that canopy relatively quick. I am not bragging, I am just saying it can be done if you plan and then execute the plan on your farm.

There will be many opportunities for you to get your plan together at the various meetings this fall, winter and spring. Attend these meetings in your county or state and put together a total farm approach for effective pigweed management.

TAGS: Management
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