What is in this article?:
- Think Like a Weed
- Defensive tactics
“The number-one thing in a resistance management program is to be aware of the weeds you have in your fields and how they got there,” says Sprague says. “It’s very important to identify weed problems correctly.
“If you see a patch of weeds from the combine seat that should have been controlled, you really need to investigate what species is there, maybe collect some seeds, gather some samples to test and find out if they’re resistant.”
There is no simple solution to the weed resistance challenges growers face today, says Owen. “In the past, every time we had a problem, a different site of herbicide action came along to take care of it. The solution to triazine resistance was ALS-inhibitors, which were then used on 85-90% of soybean acres. When weeds evolved with ALS-inhibitor resistance, we turned to glyphosate. Unfortunately, there are no new sites of herbicide activity in the development pipeline. And even if new active sites of action were discovered, they would not represent stand-alone solutions for glyphosate resistance.”
That’s why growers should incorporate as much diversity as possible in weed management programs, Sprague advises. “Use herbicides with different residuals and different effective modes of action, tillage, cover crops, crop rotation – there are many practices that can fit in a program.”
The tactics don’t have to be fancy, she adds. “If you are in the field and see suspect weeds early in the season, pull them before they go to seed. They are a lot easier to manage when they are small and immature.”
There is one tool that every herbicide-resistance management plan needs: “Soil-applied preemergence herbicides are a must,” Owen says. Relying solely on postemergence applications is no longer an option.
“Many growers don’t understand or believe that early season weed control is absolutely essential to protect crop yields. They say, ‘Man, that’s going to cost a lot of money.’ But a preemergence program doesn’t cost them anything in the long run,” he says. “When you consider the extra yield brought by better weed control, and with current bean prices, you can afford to buy a really good residual weed management program for $20-30/acre.”
Sprague cautions famers who employ diverse programs to remain vigilant about scouting for escapes. “Now that we have new infestations in the upper Midwest and understand how easily the weeds spread, we really need to keep our eyes open to the possibility of having resistant weeds,” she says. “Our focus now needs to be on preventing them from becoming widespread problems that are very difficult to control.”