In writing about how to have your best chance of success controlling Palmer pigweed in soybeans with the various technologies available, I started with LibertyLink system and a couple of articles about the use of residuals.
That got the cart a little before the horse, but residuals were what I had on my mind at the time. The use of residual herbicides is definitely one of the keys and I like the goal of getting 80 percent control pf the pigweeds with the residual component.
You will not always achieve that due to the inconsistent nature of residuals in the South. However, shooting for that goal is a good start.
Another key to success with the LibertyLink system is starting clean at planting. Perhaps the biggest mistake I saw this past year, especially later in the season, was folks planting both LibertyLink and Roundup Ready soybeans into standing 2-foot pigweeds and hitting them with a burndown — usually a high rate of Ignite.
Ignite has a lot of activity, but it is not going to kill a lot of the bigger pigweeds. When you have two trifoliate soybeans in re-growing 2-foot pigweeds, you have a problem.
If the soybeans are Roundup Ready, you can get the disk in. In the LibertyLink system, a couple of applications of Ignite will often help the situation a lot. However, if you have used 44 ounces of Ignite for burndown, by current label you have none left for in-crop use. If you use it anyway, any pigweeds that escape will have had three sub-lethal applications of Ignite thrown at them and this is a worst-case scenario for potential rapid resistance development.
If you have glyphosate-resistant weeds, the days of planting into those and nuking them with a burndown are over. Changing the program is required.
One step toward starting clean can be through the use of a preplant residual herbicide such as Valor, Envive or other Valor-containing products applied early preplant.
The choice of herbicides will depend upon what weed species you have. If resistant marestail is in the mix, for example, you may need a burndown plus residual combination. The choice of herbicide combinations is great and I am not going to attempt to go in to all of them.
The objective should be to either be clean at planting or so close to it that a burndown treatment will easily provide 100 percent control.
If you successfully use an early preplant treatment and yet have small weeds at planting, a burndown treatment that has to be considered back in the picture is paraquat (Gramoxone and others). Paraquat has lost favor through the years due to the effectiveness and low cost of glyphosate. There have also been some drift issues on wheat in the spring and most applicators in general just do not like to put it out.
However, if you have glyphosate-resistant weeds, glyphosate does not work anymore. If you burndown with Ignite, you limit the amount of Ignite that you can legally use in-crop. I think you should always assume you are going to need two 22-ounce applications of Ignite in-crop. If you get a good scald with your residual program you may get by with one.
However, I would always assume you will need two. The big advantage that the LibertyLink system has over a Roundup Ready (or conventional) system using conventional herbicides is the opportunity to use two applications of Ignite.
Another reason to consider paraquat as a burndown herbicide in the LibertyLink system is to get another mode of action into the system for resistance management. Paraquat is generally only effective on small weeds. However, is pretty hot on pigweeds and you can add a photosynthetic inhibitor herbicide such as Sencor or other metrubuzin-containing product to it and make it an excellent burn down treatment.
It is not a treatment to go out and plant into 2-foot to 3-foot weeds and expect a miracle like we got used to in the good old days of Roundup Ready. The weeds have changed. Wishing for the good old days or trying to force a treatment to be what glyphosate used to be won’t work. You simply must change with the weeds.