Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
Questions about fall panicum control have increased in recent years, and I’m seeing more fields each season with poor control.
Fall panicum is a native summer annual grass weed, characterized by thin, long leaves and a reddish coloration near the base of the stem. You can find more on its identification here https://weedid.cals.vt.edu/profile/197#. Control with S-metolachlor (Dual) and acetochlor (Harness) tends to be short-lived, with weed escapes often appearing about three weeks after application. Pyroxasulfone (found in Zidua and Anthem products) provides more effective preemergence control and is the preferred product. It’s important to apply the full labeled rate of pyroxasulfone based on soil type. Some premix products include lower rates that may not offer sufficient control of fall panicum.
Other soil-applied herbicides with good control of fall panicum include Princep, Prowl, and Command.
Here are also effective postemergence options when fall panicum is treated early—ideally when plants are less than 4 inches tall. However, fall panicum tends to be less sensitive to glyphosate compared to other grasses. For example, according to the Roundup PowerMax3 label, the maximum height for effective control at 20 fl oz of large crabgrass is 12 inches, giant foxtail is 20 inches, while fall panicum is 6 inches. Tankmixing some herbicides with glyphosate can reduce control of fall panicum, particularly when fall panicum is larger than 6 inches tall and is tank mixed with herbicides that cause leaf burn of the fall panicum (Liberty, Callisto, Reflex etc.). Enlist One tankmixed with glyphosate can also result in reduced fall panicum control
In corn (including approved sweet corn hybrids), Accent Q provides good postemergence control. Impact at 1 to 1.5 fl oz is effective in both field and sweet corn. For grain sorghum, FirstAct used with Double Team sorghum hybrids offers excellent control.
In broadleaf crops, consider adding a postemergence grass herbicide like Select (clethodim) or Poast (sethoxydim) to ensure effective control of fall panicum.