Introduction of new herbicides

By James Hoorman, Hoorman Soil Health Services

Getting a new herbicide approved may take 12 to 15 years and cost over $300 million, and that is just for the successful herbicides. The last new herbicide modes of action occurred about 40 years ago, but now several companies are finally releasing new herbicides effective against resistant weeds.

Developing safe new herbicides is a multifaceted project. First, large numbers of chemicals must be manually screened. Now with AI, this process is much faster. Today, most new herbicides are designed to be more site-specific, either for a targeted site or a weed group. After screening, it must be tested multiple times and in various ways to ensure it is biologically active and does not harm the crop. Then, environmental testing and toxicology tests are performed, followed by field testing and formulations. A new herbicide must cross several hurdles to get approved.

Bayer invests about $1 billion per year in agricultural research, seeking new herbicides and/or new modes of action. The first new herbicide is Convintro (diflufenican), a Group 12 herbicide, which, pending final regulatory approval, is effective against resistant weeds like Palmer amaranth and water hemp. Water hemp has developed resistance to at least six different modes of action, so farmers are desperate for a new herbicide to fight this weed. Since Convintro is very selective against water hemp, particularly, it will need to be combined with other herbicide chemistries to control other weeds. Convintro has been approved and used in Europe, and is now close to approval (expected in 2026) for use in corn and soybean production, both preplant and preemergence, with other herbicides.

Water hemp has become one of the most herbicide-resistant weeds. Generally, Liberty (glufosinate) sprayed as a postemergence herbicide remains an option; however, weed resistance to this herbicide has developed due to overuse. In some areas, farmers need to apply the full rate of 32 ounces of Liberty per acre to control hard-to-kill weeds. When a herbicide is used repeatedly, a few survivors pass on their genes, and soon a weed becomes resistant. Liberty Ultra Herbicide now has a new formulation to enhance its effectiveness against tough weeds. It is supposed to enhance penetration and adhere to plant leaves more effectively, providing improved weed control.

One way to enhance Liberty or Liberty Ultra (glufosinate) is to follow the labeled directions. This herbicide works best in slightly acidic water. In several cases this past year, treated chlorinated town water with a pH over 9.0 was used, which greatly reduced and compromised the herbicide’s effectiveness. Sometimes the problem is chemistry; sometimes it is related to biology when herbicide resistance occurs.

Bayer also has another new herbicide, Icafolin, that looks promising but may not be released for several years yet. Icafolin “freezes” plant growth, so the plant simply stops growing and eventually melts down and back into the soil residue. It has both foliar and residual activity and is very effective against resistant weeds, such as Italian ryegrass, in the South.

Glyphosate is used on about 90% of all farms, and with current lawsuits, it may soon be more intensely regulated. With Roundup (glyphosate), weed resistance is becoming rampant across the Midwest, and there are very few options to control resistant grass weeds. Both glyphosate and clethodim (a chemical used in Select Max) have or are developing grass weed resistance. Some grasses that become really hard to control include barnyard grass, goosegrass, and Italian ryegrass, along with broadleaf weeds in the pigweed family (Palmer Amaranth, water hemp, red root).

Sometimes farmers will make two to three herbicide passes to control resistant weeds in soybeans. With soybean yields and crop prices stagnating, many Midwest farmers are struggling to make soybeans profitable, especially if they have a weed problem. Farmers need herbicides or new weed-control strategies to enhance crop yields. Syngenta also has a new herbicide, metproxbicyclone, an ACCase inhibitor. It is good for herbicide-resistant grass weeds. Hopefully, this new herbicide will help with some of these problem weeds.

Most weed researchers say that there is no one product or herbicide that will solve the weed resistance problem. Mother Nature has a way of selecting plants that survive over time. That’s why Roundup (glyphosate) is having problems. It has been overused for over 40 years. Even with the new herbicides, herbicide resistance can occur quite quickly if they are overused. Follow herbicide protocols and rotate herbicide chemistries to avoid future weed resistance.