I will continue to discuss soil residual herbicides in future articles on Roundup Ready, LibertyLink and conventional soybean weed control programs. This week I will attempt to compare and contrast weed control programs in Roundup Ready and LibertyLink soybeans.
LibertyLink soybeans will be available to growers for the first time in 2009. My first look at them was in 1995, and at that time Roundup Ready soybeans had been in the program for a couple of years.
Even without the benefit of knowing what we do now, it was obvious at the time both technologies had a lot of similar characteristics. Both offered very broad spectrum weed control with herbicides applied right over the top of soybeans, and the soybean tolerances to the respective herbicides were excellent.
While Roundup Ready soybeans are very tolerant to glyphosate and LibertyLink soybeans are very tolerant to Ignite, there is no point in testing your curiosity to see if Roundup Ready soybeans are tolerant to Ignite and vice versa. They are not.
One of the nice things about planting all of the acreage in Roundup Ready soybeans is you did not have to keep fields straight. I am a living testament to the fact you can plant the wrong variety or get in the wrong field with a sprayer. That is why, in the early days of development, I put my entire soybean weed research program in Roundup Ready soybeans as soon as I could get enough seed.
Times have changed, however, and to implement an effective resistance management program, you must start mixing things up. It is best to mix things up before you get glyphosate-resistant weeds so you can keep the Roundup Ready technology viable on your farm.
If you do not stay a step ahead, resistance will force you to mix things up anyway. The difference at that point is that the Roundup Ready technology will have lost some of its value on your farm.
The LibertyLink system offers the first opportunity to implement a completely different herbicide mode of action while keeping the same production system you are using with Roundup Ready soybeans. If you chose to use both technologies on your farm, there are lots of ways with color coding and other means to keep fields straight.
The timing of application of the first glyphosate application in Roundup Ready soybeans and Ignite in LibertyLink soybeans is essentially the same. The University of Arkansas recommends timing the first application of both herbicides at 10 to 14 days after emergence.
To argue that application timing is more critical or less critical for killing weeds in one technology or the other would depend upon the species.
With annual grasses or non-resistant pigweeds, for example, there would be more flexibility in glyphosate timing than Ignite timing. On the other hand, with morningglories or coffeebean, for example, there would be much more flexibility in the Ignite timing.
There is also more to it than just killing the weeds. Regardless of the postemergence treatment being considered, irreversible weed competition losses begin at around 14 days after weed and soybean emergence. Therefore, killing the weeds early is equally important in Roundup Ready, LibertyLink and conventional soybeans.
Both glyphosate and Ignite are very broad spectrum herbicides. To pick one herbicide over the other would be difficult. Glyphosate would have the edge on grasses and non-resistant pigweeds; Ignite would have the edge on species such as morningglories, gourds, smartweeds, coffeebean, indigo and groundcherry.
Having both technologies available gives the grower the options of selecting the one that best fits the weed spectrum and of rotating them for a very effective resistance management program. Implementing a program with more than one herbicide system may take a little getting used to, but I believe you will find the Roundup Ready and LibertyLink systems very complementary.