By Dusty Sonnenberg, CCA, Ohio Field Leader, a project of the Ohio Soybean Council and soybean check-off.
Weed control in soybeans and herbicide trials have been the subject of research conducted in the Becks Practical Farm Research (PFR) the last several years. “There is a lot of old herbicide technology in the marketplace today. The salt in Enlist is a new formulation but the technology is still about 75 years old. Dicamba technology is over 50 years old, and Round-up (glyphosate) is over 50 years old. The newest broad spectrum herbicide on the market today is Liberty. Liberty technology is 25 years old and we are putting a lot of trust in Liberty,” said Luke Schulte, Field Agronomist for Becks. “The gravitation as inputs are very high is to pull back input selection to what you know works from 10 or 15 years ago. The reality is that with the age of some of these herbicides, even though some of the technology formulations are new; and with a new understanding of how weeds impact yields, you may need to change your mindset and focus on keeping weeds from emerging in the first place. Ultimately sustainable weed control minimizes the development of herbicide resistance. That means keeping weeds from emerging in the first place.”
Once a weed has emerged, it has the ability to impact the yield of the crop by reflecting the light and impacting the plant physiology. Starting clean is important. It is important to consider different sites of action when targeting tough to control weeds. “To have a thorough burndown, it often takes multiple sites of action,” said Schulte.” An injured weed is the hardest weed to kill. It is the one that has been injured with herbicides or tillage, and then is finally killed with the combine head.”
In findings from the study at the University of Guelph, some plants can detect competition and reflected light even before reaching the soil surface. “Soybeans are one of those plants. Soybeans can detect competition and reflected light,” said Schulte. “In the presence of weeds, soybeans will change how they grow prior to emergence. Just prior to breaking the soil surface they can alter their growth trajectory due to sensing the competition and reflected light.” Having a residual herbicide included with the burndown can help reduce this behavior. “Having a comprehensive pre-emerge plan may seem like it costs more, but it will cost less in the end by reducing the competition,” said Schulte.
PRF research from southern Illinois in 2015-2019 looking at comprehensive pre-emerge programs showed that when a program goes from a single site of action to multiple sites of action, Water hemp control improved by nearly 30%. “Generally speaking, the same applies to many of our broadleaves,” said Schulte. “The more comprehensive and less dependent we are on a single site of action, the more effective we will be on a lot of broadleaves and have better season long weed control. Those are weeds that are reflecting light and stealing yields.” It is important to make sure that different modes of action are being used, and that those modes are effective against the weeds that are most common in the field.