I hope by the time you read this we will have had a nice state-wide rain, but as I write, dry weather is driving a lot of people nuts — especially in north Arkansas. Many have quit planting and getting residual herbicides activated has been difficult.
I have been asked to help make decisions based upon what I believe the weather might do — if I could predict the weather I would not be a weed scientist. I do know that planting into a relatively dry seedbed with no forecast of a rain in sight is a crap shoot with Roundup Ready soybeans and heavy pigweed pressure. In some of those situations I have recommended getting out some Gramoxone with a Valor-containing product or in some cases Gramoxone with Authority MTZ and waiting on a rain before planting. I am much more comfortable planting Roundup Ready soybeans into an activated residual and then following with another residual at planting.
In situations where the grower is planting LibertyLink soybeans, it can be nice to plant into an activated residual, but you can take more chances. In most of those situations I have been recommending planting, if that is what the grower wanted to do, putting out a pre-emergence herbicide and hoping it gets activated. If it fails to get activated or activated timely, the weeds can still be controlled with the Liberty applications if they are timely. That is a big advantage for that technology.
Whether you plant Roundup Ready or LibertyLink soybeans, weed control this year will come down to postemergence application timing. Timing is always important, but if we continue to struggle to get residual herbicides activated, timing is going to be everything. Instead of worrying about how big a pigweed Flexstar, Blazer, Cobra or Liberty (Ignite) will kill, worry about how small a pigweed you can kill.
When you let the weeds get up to the size you have to worry about, it is too late. Pigweeds will give you about a one week grace period when they first emerge. That is about the time they turn from red to green and is the perfect time to hit them with a postemergence herbicide. Once they turn green, they quickly shift gears and begin to grow 2 inches or so per day.
In a Roundup Ready or conventional weed control program, if you fail to get residual herbicides activated and miss the first postemergence application timing by a few days, your program is dead in the water. If you have the same scenario in a LibertyLink system you are very much behind the eight ball. You can do a lot with two applications of Liberty a week to 10 days apart. If, however, you miss the timing of the first application, quite often you wind up pounding the pigweeds with sub-lethal doses and that is the ticket to premature failure of a technology.
There are a lot of first-time LibertyLink growers this year. Typically second- and third-year LibertyLink growers are doing very well with the technology. In contrast, some first-year growers have struggled. In some cases they have struggled because they did not use residuals, but in most cases it has been because they simply let the pigweeds get too large before the first application. Liberty is a herbicide that will kill a weed larger than you expect
. That can keep you in trouble all of the time. You must go with timings that work consistently.
In the Roundup Ready programs, plan to start spraying at seven days after emergence just as the pigweeds change from red to green, or about 1 inch tall. Sure, you might kill a 2- or even 3-inch pigweed with Flexstar, but they will be there in one to two days! In a LibertyLink system, target the first application at 10 to 14 days after emergence, but do not hesitate to spray some at seven days if that is what it takes to get over all the acreage timely. I have never had a failure call because someone sprayed their first postemergence herbicide too early.