Palmer amaranth plagues many U.S. soybean farmers, and its resistance to glyphosate makes controlling this weed an even greater challenge. Farmers in the southern region of the United States know about this wicked weed all too well, while farmers in other parts of the United States are just beginning to deal with its wrath.
Due to excessive use of glyphosate as a control measure for Palmer amaranth, this herbicide is no longer a reliable option for farmers. In addition to glyphosate, Palmer amaranth can also exhibit resistance to ALS inhibitors, primarily in the southeast. This leaves some farmers relying heavily on PPO inhibitors in both pre- and post-emergence herbicide applications. In order to avoid further resistance issues, reliance on PPO inhibitors must be reduced.
Metribuzin is a viable pre-emergence herbicide option for controlling Palmer amaranth, reducing the need for PPO inhibitors. However, North Carolina State University extension weed specialist Wesley Everman, Ph.D., cautions that care must be taken when using metribuzin to avoid soybean injury. Everman encourages farmers to consider the following factors when using metribuzin in soybean fields:
- Variety Selection. Choose a variety that is metribuzin-tolerant.
- Soil type. Avoid using metibuzin in sandy soils.
- Organic Matter. Do not use in soils with less than 0.5 percent organic matter.
- pH: Avoid planting soybeans and using metribuzin in soils with a pH higher than 7.5.
- Planting Depth: Plant soybean seeds deeper than 1.5 inches.
- Rainfall: Try to avoid applying metribuzin before heavy rains.
- Use Rate: Refer to product recommendations for different rates based on soil type.
“Palmer amaranth has changed the way we manage the weed in the south and forced many to adopt old herbicide technologies,” says Everman. Metribuzin is one of those technologies, but take caution to avoid injury potential.