Hopefully, you laid a good foundation for weed control for the season with residual herbicides. Then, tweak your post applications based on weeds in the field and the herbicide-tolerant traits in your soybeans. That’s the advice Bill Johnson offers when asked what to spray postemergence in soybeans.
“If your soil-applied products did their job, you’re looking at taking out escapes,” he says. “What you use will depend on the tools available to you and weeds in the field.”
Here are two examples which illustrate how Johnson thinks through post-herbicide approaches. He evaluated these two fields virtually.
Grasses and broadleaves
In Field 1 (photo at top), Johnson obviously spotted the tall grass. He also noticed some broadleaves, including cockleburs. “Glyphosate will get the grasses as long as you apply at labeled rates and weeds are actively growing,” he says.
There are reports that barnyardgrass has been tougher to kill with glyphosate in some instances in recent years, but no one has documented actual resistance in barnyardgrass to glyphosate. Strong rates and good growing conditions would be important.
Glyphosate will likely need some help on the broadleaves, Johnson says. If soybeans are Xtend or XtendFlex varieties, you could use dicamba, or if they’re Enlist E3 soybeans, you could apply 2,4-D choline. Both would help on the broadleaves. If those aren’t options, there are other herbicides you could add to glyphosate. Some of these could produce temporary burn on upper soybean leaves,
It’s questionable whether the grass and weeds in this field have provided enough competition to hurt final yield, Johnson says. The grass isn’t overly thick, and the broadleaves are small. However, applying a post application soon would be critical. Broadleaves are easier to control while small.
CUSTOMIZE THE APPLICATION: Bill Johnson advises using the best herbicide tools available to you to tackle the weeds in this field (Field 2 in the article). (Tom J Bechman)
You might also consider adding a strong residual herbicide, such as Zidua, with the post application, Johnson says. Maybe you need to consider beginning with a stronger residual herbicide program next season in beans as well.
Winter annuals, perennials
Field 2 (photo within article) may look less challenging from the road, but once you identify the weeds present in the field, you would realize you still need the proper post-herbicide choices to ensure control. “I spotted cross-leaf groundsel, which is a winter annual, and dandelion, a perennial, still in bloom,” he observes.
Add in grasses in the field, and it calls for a broad-spectrum post-herbicide approach, he says. A systemic herbicide like glyphosate will pick up groundsel and help on dandelions. Adding Classic would also help knock out the dandelions for this season.
Again, if they’re Xtend or XtendFlex soybeans, glyphosate plus dicamba would be a good option. For Enlist E3 soybeans, you could apply both glyphosate and 2,4-D choline. Pay attention to label recommendations and restrictions when applying post-herbicide products.