I ended my last article writing about days after emergence (DAE) for timing postemergence herbicides, and stated the best timing for the first Ignite application in a LibertyLink system is seven to 10 DAE.
Dick Oliver at the University of Arkansas deserves most of the credit for devising this method for timing postemergence herbicide applications. This method originated back in the days of our reduced rate postemergence programs with herbicides like Basagran and Blazer where we based the herbicide rate on the weed size.
The success of the reduced rate program was strictly dependent upon getting an accurate measure of the weed size and knowing something about the growing conditions.
When only weed size is used, growers have a tendency to underestimate the size — I used to jokingly say they only measured the smallest ones.
Also, the day they are measured may not be the day they are sprayed. With a weed like Palmer pigweed, a delay of a couple of days can mean a world of difference in weed size.
In addition, when you say the weeds are 3 inches tall, that does not tell me anything about the growing conditions, even if the measurement is accurate.
When DAE (on the day of spraying) is used for timing, or at least is used in conjunction with weed size, and you tell me the weeds are 10 days after emergence, I have a couple of more valuable pieces of information.
First, I know they can not be much larger than I would expect because the size can not be underestimated and they can not be too large for the application in 10 days.
Second, I also know something about the growing conditions. Normally soil moisture is the most critical factor in determining herbicide activity. I know if there was enough moisture for the crop and weeds to germinate, they will not be drought-stressed by 10 DAE.
While you may to choose to also consider weed size when timing herbicide applications, I would challenge you to consider DAE as well. I believe you will find it a very valuable tool.
Through the years, the most common question regarding the DAE method of timing herbicide applications has been, “Are you talking about weed or crop emergence?” It is actually weed emergence, but crop emergence is usually the most practical way to keep up with it.
Our warm season weeds like similar soil temperature and moisture conditions as soybeans. Therefore, the weeds will begin to germinate and emerge about the time the soybeans do.
While you may not be keeping up with when the weeds emerged, you will usually know when the soybeans emerged. Therefore, it is more practical to record crop emergence dates.
Some growers have tweaked the DAE system by taking the planting date (a commonly recorded statistic) and adding the approximate number of days it is taking soybeans to emerge during that time of the year. With that method, if you are targeting 10 DAE for your first herbicide applications and soybeans are emerging in about five days, you would just use 15 days after planting.
There can be exceptions to the weeds emerging with the crop but not very often. One could argue that if you got a perfect two weeks of residual control from a pre-emergence herbicide, the crop could emerge weed-free. While this is true, it will not happen very often.
Remember, all of the weeds do not have to emerge with the crop to require a postemergence application — just some of them.
Regardless of how you choose to manage postemergence herbicide timing, we are moving back into an era where timing is going to be more important than a lot of growers have regarded it in recent years.
This is true whether you are trying a conventional system, trying to manage resistant weeds in a Roundup Ready program or timing Ignite in a LibertyLink program. Find a timing method that works best for you.
Regardless of the cropping system you are using, however, you will rarely mess up by timing your first postemergence application within the first seven to 10 days after crop emergence.