With harvest now in full swing Paul O. Johnson, SDSU Extension weed science coordinator, reminds farmers not to forget their fall weed control.
"What are the weeds that are left in your crop? Do you know which weeds they are? Is there a weed that you do not know and how large is it? Does it look like the weed was not controlled at spraying time? Did you have an herbicide failure or is it a weed that your product does not control," Johnson asked. "As you move away from glyphosate products it is important to read labels closely to insure they control the weeds in your field."
Johnson said harvest is the time to identify these problems so next year they are not a problem again.
"This year again there was a lot of late weed emergence after normal spraying was done. When there is moisture in August, it is likely that curtain weeds like common waterhemp and velvetleaf will emerge late and still put on seed before harvest," he said.
Johnson explained that this only can be controlled if the herbicide products used have enough residual to keep these seeds from being able to emerge and grow. "Back in the 1980s and early '90s late emerging weeds like waterhemp and velvetleaf were very common in all fields but for sure in soybeans."
The 2014 growing season has seen isolated cases of black nightshade.
"Glyphosate has been very deadly to nightshade and still is, but where glyphosate was not used, that is where the problems showed up," Johnson said.
If there is an unknown weed, while reviewing weed issues in fields this harvest, contact SDSU Extension.