While the issue of herbicide resistant weeds is at an all-time high, it’s not because of GMO crops. In fact, certain weeds have shown herbicide resistance for nearly 60 years while glyphosate-resistant weeds have only been around for 20 years.
In 1957, spreading dayflower proved resistant to synthetic auxin herbicide (group 4) in Hawaiian sugarcane fields, according to the Weed Science Society of America (WSSA). In the same year Ontario, Canada found wild carrot resistant to the same herbicide.
In nearly 60 years, 250 weed species have developed resistance to 160 herbicides in 23 of the 26 current herbicide modes of action. These weeds can be found in 86 crops spanning 66 countries, says WSSA.
Weeds don’t become resistant because of GMO crops: There is no cross pollination that turns weeds into some super mutant that withstands any herbicide, according to weed scientists.
Instead, the evolution is simple. One or two weeds will frequently have natural resistance to a herbicide, and when the same mode of action is used time after time, these plants survive. Those weeds go to seed and begin to spread. Then what started as a small, isolated problem explodes into the field as weed seeds spread from farm to farm, state to state, and even country to country.
What can farmers do? Use a systems approach, urge weed scientists. That means:
1. Don’t rely on a single mode of action.
2. Check to ensure that the mix of herbicides sprayed are effective against the weeds targeted.
3. Consider mechanical weed control such as tillage.
4. Don't expect a new herbicide mode of action to save the day.
“It would be naïve to think we are going to spray our way out of resistance problems,” says Stanley Culpepper, weed scientist at the University of Georgia. “Although herbicides are a critical component for large-scale weed management, it is paramount that we surround these herbicides with diverse weed control methods in order to preserve their usefulness--not sit back and wait for something better to come along.”
What weed control methods have you found most effective on your farm? Ineffective? Let us know in the comments.