Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
Fall panicum control was one of the most frequent discussions that I had last year. Again this year I am seeing a lot of fall panicum in fields (https://weedid.cals.vt.edu/weedimg/197). Fall panicum is a native summer annual grass weed. Control with s-metolachlor (Dual) and acetochlor (Harness) is relatively short and we start to see breaks after about three weeks. Pyroxasulfone (Zidua and Anthem products) provides better preemergence control.
Fall panicum is one of those species that is not as sensitive to glyphosate as other grasses. The Roundup PowerMax label says for effective control at 22 fl oz the maximum height of large crabgrass is 12 inches, giant foxtail is 20 inches, while fall panicum is 6 inches. Accent Q will provide good control in corn (including approved sweet corn hybrids). For broadleaf crops, consider including a postemergence grass herbicide such as Select (clethodim) or Poast (sethoxydim) to improve control.
It appears tankmixing some herbicides with glyphosate can reduce control. Last year we saw this when fall panicum was large (above 6 inches tall) and glyphosate was tank mixed with herbicides that caused leaf burn of the fall panicum (Liberty, Callisto, Reflex etc.). It appears the key to successful control is spraying while fall panicum plants are small and susceptible.