In a system of residual herbicides in a LibertyLink program you are not as dependent on residual herbicides as you are in a resistant Palmer pigweed situation with a conventional herbicide program or Roundup Ready program.
The reason is Ignite herbicide in the LibertyLink system has much better postemergence activity on glyphosate-resistant pigweeds than either conventional herbicides or glyphosate tank-mixed with conventional herbicides.
However, the use of some residual herbicides to reduce the pigweed population — both initially and later on — and to reduce the annual grass infestation is a highly recommended practice.
In addition, mixing modes of action from the beginning will help keep us from going down the same path in LibertyLink soybeans that we went down previously with Roundup Ready.
I occasionally get comments that “you didn’t mention a particular herbicide in a place in an article where that product may have had a fit.” I usually mention specific herbicides as examples in situations where a lot of different things may work.
Because there are so many generics as well as package mixes now, it is impossible to mention them all or even keep up with them. Heck, I am too old to even try!
With residual herbicide programs there are countless ways to go. The broad categories for residuals break down into preplant surface-applied treatments like Valor, Envive, Enlite, and other Valor-containing products, preplant incorporated treatments like Dual and Treflan, pre-emergence treatments like Prefix, Dual and Authority MTZ, and adding Dual or a similar product to an early postemergence application.
In a LibertyLink program, you need to pay more attention to annual grass control with residuals than in a Roundup Ready program. I have been pleasantly surprised at how good two timely applications of Ignite can be for annual grass control.
However, if you miss the timing and the grass (especially barnyardgrass) gets too big, you can have difficulty in high populations. In a lot of LibertyLink programs, a preplant incorporated or pre-emergence application of Dual alone may be all that is needed for both grasses and to reduce the pigweed population.
If you want more pigweed control, an application of Valor or Envive seven to 14 days prior to planting can be an excellent treatment. If you use Valor alone, you may still need a pre-emergence grass herbicide later if you have heavy barnyardgrass pressure.
Envive contains Valor, Classic and Harmony, which can increase the grass control over Valor alone, but you cannot plant rice the next year if the soil pH is above 7.
An excellent pre-emergence herbicide for both grass and pigweed control in a LibertyLink program is Prefix, which contains Dual and Reflex. It has been the standard for comparison in the University of Arkansas pigweed trials that I have observed.
In most situations, a pre-emergence application of Prefix followed by two timely applications of Ignite will be hard to beat.
In the LibertyLink program, you can use Prefix without having to worry about how much Flexstar you may need later (because of label restrictions), as you do in a conventional or Roundup Ready program.
There are other examples of pre-emergence herbicides like Authority MTZ or Sencor that can fit here as well.
For more of a program approach with residual herbicides, I have seen some growers using something like an early preplant treatment containing Valor and then adding some Dual to the first Ignite application.
As I have stated in some other articles, it is often more important that you just do something than specifically how you go about it.
In any residual herbicide program, moisture for activation is the key to success. In the wet years, residuals are a great tool. The key to consistent overall weed control though is getting maximum efficiency from the postemergence program.
Next week we will look at the keys to making Ignite a great postemergence treatment.