Future weed control — look to the past
Aug 20, 2009 2:45 PM, By Ford L. Baldwin, Practical Weed Consultants, LLC.
I am enjoying the e-mails I am receiving from around the country regarding Palmer pigweed. Several have related their experiences with glyphosate-resistant pigweeds — some good and some not so good. Others have e-mailed just to tell me they suspected they might have had a problem last year and this year those suspicions have been confirmed.
Recognition of the problem is the first step in trying to correct it. A lot of folks recognize the problem now, I just wish more did.
Who would have ever thought some farmers would be running hoe crews through Roundup Ready soybeans!
Different farmers will take different approaches to attempt to solve the glyphosate resistance problem.
First, if you do not have the problem yet, do everything possible through rotation with crops such as corn where you can use conventional chemistry. In addition, rotate to LibertyLink soybeans to break the glyphosate cycle in the soybean crop.
I try to say at least once in every pigweed article that if you can prevent glyphosate-resistant pigweeds, then you keep glyphosate as useful on your farm as it ever was. Unfortunately, many growers seem hell-bent to drive it off the cliff, and I have looked at thousands of acres in recent weeks where glyphosate may never be as useful as it once was.
In order to consider different control strategies, perhaps it will be helpful to look at where we have been. Most things tend to run in cycles and weed control is no different.
In the 1950s and 1960s, the major weed problems in most row crops were annual grasses, johnsongrass and pigweeds. The major breakthroughs on annual grasses and pigweeds came with soil residual herbicides such as Treflan, Karmex, Cotoran and Atrazine — depending on the crop.
Some of the residuals like Treflan and similar herbicides to follow had to be incorporated into the soil and some like Cotoran and Atrazine could be used incorporated, pre-emergence or postemergence.
For a long period of years, most of the soil residual herbicides were preplant incorporated — a practice seldom used today. These herbicides were excellent on grasses and pigweed and two major things happened as a result.
First we became so efficient at grass and pigweed control that weed shifts occurred to more difficult to control weeds. The other thing that happened was a boom in the development of new soil residual and postemergence herbicides.
As better postemergence herbicides such as Basagran, Blazer, Reflex, Poast, Fusilade, Assure and Select were developed, the pendulum began to swing in favor of postemergence treatments because they were easier to use. In addition they were often more consistent than the soil residual herbicides that required rainfall for activation.
Still, throughout the 1970s, 1980s and early 1990s, a typical soybean and cotton weed control program used a combination of soil residual and postemergence herbicides.
When the Roundup Ready soybean and cotton technology really got up to speed, the program approaches for weed control quickly went by the wayside and total postemergence weed control programs have been used exclusively by most farmers ever since.
With the resistance issues facing the Roundup Ready technology, the pendulum is going to swing back toward the use of more residual herbicides. That means weed control has become less simple than most have grown use to.
With that will also come the frustration that sometimes they do not work. This was a great year for residuals with abundant moisture all season. In a dry year they can look much different.
In addition to the use of residuals, the three most important factors in a weed control program will again become timing, timing and timing. Glyphosate has been so forgiving that many growers never knew we used to have to time postemergence applications at seven to 14 days after weed emergence.
We will have fun with these principals in the next weeks in conventional, Roundup Ready and LibertyLink soybeans.
e-mail: ford@weedconsultants.com
