A new 2020 United Soybean Board-funded Take Action herbicide classification chart is now available to farmers and the ag community.

Available as a poster, a downloadable graphic, in a booklet or as a phone/desktop app, the Take Action herbicide-resistance management chart helps growers effectively select herbicides to minimize weed resistance while controlling weeds.

The materials can be downloaded at www.iwilltakeaction.com/kit. Scroll down to click on the Take Action charts for herbicide classification, fungicide classification and insecticide classification. There’s also a fungicide efficacy fact sheet.

In addition to the United Soybean Board funding, Take Action is endorsed by Cotton Incorporated, Valent, Corteva Agriscience, National Association of Wheat Growers, Weed Science Society of America, BASF, Sorghum Checkoff, Herbicide Resistance Action Committee, Bayer, National Corn Growers Association, FMC, Syngenta and the American Soybean Association.

The left side of the chart breaks down each herbicide by mode of action, while the right side focuses on pre-mixed multi-herbicide products. The modes of action are unchanged from the 2019 herbicide classification chart.

“When we think of herbicide mode of action, we’re really thinking about the physiological or biological processes that can occur within that plant that are impaired or inhibited by the herbicides,” said Christy Sprague, professor at Michigan State University. “It’s really how that herbicide works.”

One example is the growth regulator. When a growth regulator herbicide is applied, something is going to cause “twisting” in plants. There is generally some sort of symptomology that can be seen.

Another example of a mode of action is a pigment inhibitor. These herbicides cause whitening of plants.

The entire list of modes of action includes lipid synthesis inhibitors, amino acid synthesis inhibitors, growth regulators, photosynthesis inhibitors, nitrogen metabolism inhibitor, pigment inhibitors, cell membrane disrupters, seedling root growth inhibitors, seedling shoot growth inhibitors, and undefined.

In contrast, herbicide site of action refers to the physical location within a plant where the herbicide binds. This is where the herbicide works.

“The easy thing to think of is ‘How?’ for mode of action, and ‘Where?’ is the site of action. Within herbicide mode of action groups, there are site of action groups,” Sprague said.

To use the chart effectively, the farmer needs to know from past experience what herbicides no longer work on various weeds. This might be easy to determine if resistance is widespread for a certain weed. There are also diagnostic clinics that will test weeds for resistance to different herbicides.

Once a weed is resistant to a specific site of action, herbicides within that same site of action group will no longer work.

For instance, under the mode of action: Amino Acid Synthesis Inhibitors, there are two site of action groups. One is the EPSP Synthase Inhibitor known as glyphosate, that has 15 resistant weed species in the U.S. The other is the ALS Inhibitors that include 32 active ingredients. For this site of action, there are 47 resistant weed species in the United States.

Pre-mixed herbicides are listed on the right side of the Take Action chart.

For example, Capreno is a pre-mix of two herbicide active ingredients – Group 2 and Group 27 site-of-action products.

“When we’re thinking about trying to either delay or help manage herbicide resistant weeds, it’s really important to rotate among effective herbicides with different herbicide sites of action,” Sprague said. “We really need to be thinking about what herbicides are specific to controlling the weeds, as well as different herbicide site of action groups.

“The key things to remember is that we want to maintain great diversity – diversity with herbicide site of action, and also to rotation among effective herbicide site of action groups,” she added.

Having this information can help farmers determine what products will control specific resistant weeds.

Example

Problem: Glyphosate-resistant horseweed or marestail is a huge problem across the United States.

Possible solutions: Program 1 – Glyphosate (Group 9) plus 2,4-D (Group 4) as a burndown and then glyphosate plus First Rate (Group 2) during the growing season. There are three different site of action products.

Program 2 – Glyphosate (Group 9) plus 2,4-D (Group 4) as a burndown. Valor XLT (Group 14 and Group 2) as a pre-emergence with residual control. Liberty Link soybeans tolerant to glufosinate (Group 10). There are five site of action products.

Marestail is an annual weed that is native to the U.S. It can germinate 8-9 months out of the year. It can adapt to fall or spring germination, and once it gets to the rosette stage, marestail grows quickly. Each plant can produce up to 200,000 seeds that spread far and wide in the wind.

Controlling marestail is best achieved when the plants are very small and can be difficult to control in no-till soybeans.

On this particular farm, marestail has been selected with Group 2 and Group 9 herbicide resistance. That means Program 1 only offers one working site of action – Group 4 found in 2,4-D.

In Program 2, marestail is not resistant to Groups 4, 10 and 14. Greater diversity should mean that marestail will be controlled and not selected to develop resistance.

“So if you’re trying to manage something like herbicide resistant marestail, which program is going to look better? The one where we have three different herbicides site of action groups,” said Sprague. “The more effective herbicide site of action groups that we’re applying, the better off we are.”

To download the 2020 USB Take Action herbicide classification chart or app, please visit iwilltakeaction.com. Fungicide and insecticide classification charts are also available.