I ended last week’s article by writing that the key to a soybean weed control program is making the postemergence herbicides work properly.

Soil-applied herbicides are coming back around to playing an increasing role. However, you must be prepared for the weeds they do not control.

A soil-applied herbicide can provide anywhere between 0 and 100 percent control. Normal expectations should be somewhere in between.

In most cases you will always have weeds to control postemergence. The postemergence herbicide program gives you the last chance before the combine to control the weeds.

The reason I believe the LibertyLink system gives you the best opportunity to control glyphosate-resistant Palmer pigweed is Ignite has the best postemergence activity on them. However, to make Ignite a successful pigweed herbicide, it must be used differently than glyphosate has been used on susceptible pigweeds.

Unless they are resistant, the pigweeds in general are among the most susceptible species to glyphosate. Because of this, there has been a lot of flexibility in rates and timing to control pigweeds in a Roundup Ready program.

With Ignite, the pigweeds are not among the most susceptible species. Therefore, you must learn to make it a successful pigweed herbicide just as you had to learn to make glyphosate a successful morning-glory herbicide, for example.

The most important factor in making Ignite a successful pigweed (and annual grass) herbicide is application timing. In fact, the three most important factors are timing, timing and timing.

I have heard some say that application timing was a big disadvantage for Ignite compared to glyphosate. I have heard others say that if the timing was that critical that it sounds just like Blazer, Flexstar and other “older” herbicides we used to use.

If one just picks glyphosate-susceptible Palmer pigweed for the comparison, you can kill a big one with glyphosate easier than you can with Ignite. On the other hand, you can sure kill a bigger resistant pigweed with Ignite than you can with glyphosate.

Those are moot arguments for several reasons. First, the recommended timing of glyphosate and Ignite in an overall weed control program is very similar. In the University of Arkansas MP 44, the recommended timing for the first application of glyphosate in a Roundup Ready program is 10 to 14 days after weed emergence and for Ignite in a LibertyLink program it is seven to 10 days after emergence.

We have far too much barnyardgrass going to seed in Roundup Ready soybean fields today simply because too many growers are applying glyphosate too late.

Another reason that arguments about application timing are moot is irreversible weed competition begins at around 14 days after emergence. That means as application timings are delayed later than 14 days after emergence, yield losses begin to occur that can not be recovered.

Obviously the later you wait, the greater these losses become.

Regardless of the arguments, early timing of any postemergence herbicide is simply a sound weed management principle. Growers have learned that on some species with glyphosate they could fudge the timing.

The same is true with Ignite on species like morning-glories and smartweed. Sometimes you can even kill a bigger pigweed than expected with Ignite.

I have often stated in jest that the worst characteristic a herbicide can have is the ability to control big weeds sometimes. The ability to kill a big weed sometimes often leads to the thinking that you can do it every time and the end result is often failure.

To consistently control Palmer pigweed in LibertyLink soybeans, the first application needs to be made at seven to 10 days after emergence — 14 days at the latest.

I hear some saying that is a 2- to 3-inch pigweed. I would say start at 1-inch and hope you get them sprayed by 3 inches.

Next week I will state again why I like days after emergence better than weed size for timing herbicide applications.

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