The idea of rotating herbicide chemistries, or using multiple modes of action, is well understood by most farmers faced with tough-to-control weeds. But the request Bryan Perry made of farmers attending the annual BASF Fields of Opportunity meeting earlier this week was not about that practice. Instead, Perry, a senior soybean market manager for the company, asked farmers to add at least one new site of action to the herbicide programs they adopt for 2013.
Site of action is a phrase farmers can expect to hear weed-control experts refer to more often in the future. While the industry often uses the terms site of action and modes of action interchangeably, there is a distinct -- and important -- difference between the two.
Mode of action is how an herbicide controls a weed. Site of action is where the herbicide controls the weed. BASF describes it as the "biochemical site where an herbicide binds and disrupts normal plant growth and development."
Consider this simple analogy: When driving a car, your final destination representa site of action.
Farmers who use products that address more than one site of action for weed control are able to reduce stress in their crops which, in turn, protects valuable yield potential, says Luke Bozeman, BASF technical market manager.
"It emphasizes the need for farmers to take a systems approach to herbicide use for weed control," Bozeman says.
But why should you care about the where of weed control, you ask?
Because, weed control experts have learned that in the battle to prevent or control weeds, attacking them in multiple locations makes a good control outcome easier to achieve and more comprehensive in the process.
That’s good news for farmers who have seen their weed problems, especially resistant weeds, multiply in recent years. BASF reports that approximately 50% of U.S. farmers are experiencing some level of weed resistance in their fields today. In addition, as of 2012, the company reports that approximately 57% of the corn and soybean acres in the United States are affected by waterhemp and Palmer amaranth.
"Just three years earlier, in 2009, that percentage was 26%," says Bob Yaklich, senior corn market manager for BASF. "Essentially, we saw a doubling of the amount of acres affected by these two weeds in just three years."
The sites of action pinpointed for herbicides to work in are located in a variety of areas within plants -- below ground in weed roots and shoots and above ground in foliar parts of plants.
Once an herbicide arrives at its targeted site, the product may work in a variety of ways. Some prevent the weed from ever emerging. Another site of control enables an herbicide to halt normal shoot development. In foliar parts of weeds, an herbicide might work in the plant-growing points and cause rapid, uncontrolled growth that can’t be sustained.