By Dusty Sonnenberg, CCA, Ohio Field Leader, a project of the Ohio Soybean Council and soybean check-off.
When you think about all the management practices preformed on a soybean field, such as tillage or foliar feeding, the most common thread among high yielding soybeans is planting as early as you can,” said Luke Schulte, Field Agronomist for Becks. “The risk of early planting is a higher volume of cold fronts with cold wet soils. Those conditions can impact soybean growth and herbicide metabolism. Injured soybeans may not metabolize certain herbicides as efficiently when injured.” Yield loss can occur if there is injury to beans, but also if there are weed escapes from the pre that need to be contended with in the post application.
When going into a season, the weather and growing conditions need to be taken into consideration when implementing a herbicide program. “Group 14 chemistries are very good chemistries. Products like Sonic, Authority, and Valor are all group 14’s, but they can also be tough for a soybean plant to metabolize when there are stress conditions on the plants. That is when you should consider other options,” said Schulte. “I am not endorsing any particular herbicides. Products like Valor XLT or Boundary plus First Rate are good options for effective control with improved crop safety under those conditions.”
Early soybean planting has been proven to increase yields. “We don’t want to discourage someone from planting soybeans early, but it should not dictate a reduction in the pre-emergent herbicide program,” said Schulte. “I would recommend an adjustment that could minimize injury if cool wet conditions occur early.”
Late weed species can also be an issue impacting yields. “Late weeds typically emerge after the pre-emerge begins to break down,” said Schulte. “This is about a month later and pre-emerge herbicides do not typically last long enough to fit some of the grasses or weeds like water hemp.
For populations like palmer amaranth, water hemp, and grasses that emerge significantly later, in-season residuals that are applied prior to the pre-emerge running-out make sense.”
Group 15 products do not have an impact on emerged weeds. “It is critical that products like Warrant, Zidua, Outlook, and Dual reach the soil surface,” said Schulte. “Once the soybeans canopy, these products are not going to provide the value for your investment because they are not going to touch the already emerged weeds. These need to be applied prior to weed emergence to provide control before the soybeans canopy and before the pre-emerge herbicide runs-out.”
Based on the PRF research, a pre followed by a post herbicide application versus a pre followed by a post, plus an overlapping residual (Warrant in this study) increased the season ending by 6% when it came to water hemp control. While that does not seem worth the investment, the reduction in weed pressure was equal to about 17 million viable seeds, which is the equivalent of 3 boxes of beans.
It is important not to skip or ignore the value of post applications. The University of Tennessee has confirmed dicamba herbicide resistant water hemp. Dr. Kevin Bradley and Purdue are screening for Liberty resistance. “When there is concern level about weed tolerance or resistance to herbicides, we need to do what we can to preserve the technologies we have,” said Schulte. “Up until last year we did not have any Liberty resistance in the Becks marketing area. Now Palmer Amaranth has been confirmed.” These herbicides need to be managed appropriately to preserve the value they bring.