Introduction of New Herbicides
Getting a new herbicide approved may take 12–15 years and cost over $300 million dollars. That’s 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 weed resistant weeds.
Developing safe new herbicides is a multi facet project. First, large numbers of chemicals have to be manually screened. Now with AI, this process is much faster. Today most new herbicides are designed to be more site specific for either a targeted site or a weed group. After screening, it has to be tested multiple times to make sure it is biologically active but also does not harm the crop. Then environmental testing and toxicology tests are performed followed by field testing and formulations. A new herbicide has to cross several hurdles to get approved.
Bayer invests about 1 billion dollars per year in agricultural research looking for new herbicides and or 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 but now is close to approval, expected in 2026, for use in corn and soybean production both pre plant and pre emergence with other herbicides.
Water hemp has become one of the worst resistant weeds to most herbicides. Generally, Liberty (glufosinate) sprayed as a post emergence herbicide is still an option; however, there is some weed resistance to this herbicide 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 over and over, 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 better to give improved weed control. One way to enhance Liberty or Liberty Ultra is to follow 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 and this greatly reduced and harmed the effectiveness of the herbicide. Sometimes the problem is chemistry; sometimes it is related to biology when resistance to herbicides occurs.
Bayer also has another new herbicide called 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 like Italian ryegrass in the South.
Glyphosate is used on about 90 percent 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, the chemical used in Select Max, have or are developing grass weed resistance. Some grasses that are becoming really hard to control include barnyard grass, goosegrass and Italian ryegrass along with broadleaf weeds in the pigweed family including Palmer amaranth, water hemp and red root.
Farmers sometimes have to make two to three herbicide passes to control resistant weeds in soybeans. With soybean yields and crop prices stagnating, many farmers in the Midwest are having difficulty making soybeans profitable, especially if they have a weed problem. Farmers need new herbicides or new strategies for controlling weeds to enhance crop yields. Syngenta also has a new herbicide called metproxbicyclone which is an ACCase inhibitor and is effective on resistant grass weeds. Hopefully this new herbicide will help with some of these problem weeds.
Most weed researchers say 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 has problems. It has been overused and has been around for over 40 years. Even with new herbicides, resistance can occur quite quickly if they are overused. Following herbicide protocols and rotating herbicide chemistries are critical to avoiding future weed resistance problems.