Link up with new soybean system

At the time I penned this article in November, July 2010 soybeans were trading for $9.72 per bushel. Thus, interest in soybean production remains strong. One of the newest weed management tools to hit the market is the LibertyLink soybean system. Many growers are counting on this system to help them control glyphosate- and ALS-resistant weeds. This system can work, but it’s not foolproof. Here are some useful tips based on my experiences.

LibertyLink soybeans were engineered to have resistance to over-the-top applications of Ignite (glufosinate). The resistance gene was obtained from soil bacterium. Applications of Ignite to conventional or Roundup Ready soybeans will result in severe crop injury or death. Therefore, it is important to keep seed bags separated at planting time.

Key Points

• LibertyLink soybeans can be used to battle resistant weeds.

• Ignite works best when Palmer amaranth is shorter than 3 inches.

• Ignite requires higher water volumes than glyphosate treatments.

Ignite is not the same herbicide as Roundup (glyphosate). There are significant differences in their modes of action, movement in the plant and spectrum of weed control. For example, Roundup is more effective on annual grasses while Ignite is more effective on morningglory species. I strongly urge you to contact your local Extension weed scientist for more information about the anticipated performance of Ignite in your state.

Since 1996, soybean growers have become accustomed to applying glyphosate in low water volumes to larger weeds and achieving a reasonable level of success (that is, until resistance developed). I can assure you the LibertyLink system will be less than successful if applied in the same fashion.

Most weed scientists will tell you to apply Ignite in a minimum of 15 gallons per acre using a spray nozzle tip that provides superior coverage. I have used 11002DG nozzles in all my weed control tests and have yet to see them fail! Other nozzles will do equally as well.

It is also important to note that Ignite should be applied before weeds exceed 3 inches in height. Yes, that’s 3 inches!

Results from 2009 field trials suggest a residual herbicide is needed in the LibertyLink system. For glyphosate-resistant Palmer amaranth control in soybeans, I prefer a preemergence application of Boundary (Dual plus Sencor), but there are others. If you are reluctant to use a residual herbicide in the LibertyLink system, let me remind you that this is one reason why glyphosate resistance has become such a big issue. Let’s not make the same mistake twice!

Perhaps the biggest concern for me with the LibertyLink system is variety performance. Varieties specifically adapted for the Southeast were limited in 2009. Hopefully, you have identified a variety that has performed well in your local soybean variety tests. Based upon University of Georgia soybean production budgets and a $9-per-bushel selling price, dryland growers will need a LibertyLink soybean variety that has the potential to make at least 30 bushels per acre to cover variable expenses.

The LibertyLink system will certainly be a welcome addition to the soybean
weed-control arsenal. As with any new technology, it may be wise to experiment with this system on a portion of acres until you obtain a better understanding of variety performance and learn the nuances of Ignite. My best wishes for 2010. As always, good weed hunting!

Prostko is an Extension weed scientist for the University of Georgia.


INJURY: Ignite damaged this conventional soybean variety (i.e. non-LibertyLink).

This article published in the January, 2010 edition of SOUTHERN FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.