University of Illinois

No. 9/May 21, 1998

Postemergence Herbicides
for Grass Control in Corn

There are several herbicide options available for postemergence grass control in corn. Some of them require special corn hybrids, such as Roundup Ready (RR), Liberty Link (LL), Sethoxydim Resistant/Poast Protected (SR/PP), or Imidazolinone Resistant/Tolerant (IR/IT). Products such as Accent, Accent Gold, Basis, Basis Gold, Celebrity, and atrazine do not require special corn hybrids.

Maximum grass size: Atrazine + oil controls some annual grasses less than 1.5 inches in height. Basis provides control of foxtails, barnyardgrass, and fall panicum 2 inches in height or less. Accent Gold, Basis Gold, or Lightning (IR/IT hybrids) controls grasses up to 3 inches in height, while Accent or Celebrity controls grasses up to 4 inches. Poast Plus, applied to SR/PP hybrids, can control grasses 6 to 8 inches in height, and Roundup Ultra, applied in RR corn hybrids, controls grasses 5 to 12 inches in height.

Maximum corn size: Accent Gold and Basis Gold may be applied to corn up to 12 inches in height or at the V6 stage, whichever is more restrictive, while Basis may be applied to corn up to 6 inches tall or at the V2 stage. Accent may be applied broadcast to corn up to 20 inches in height or exhibiting six leaf collars, whichever stage is more restrictive. Lightning should be applied before corn reaches 18 inches in height, while maximum corn size for Roundup Ultra and Liberty is 24 inches. Make only one postemergence application of Roundup Ultra in RR corn per season.

Adjuvant selection: Always consult the herbicide label for adjuvant selection, as options may vary with the herbicide, tank-mix partner, and environmental conditions. Some herbicides, such as Roundup Ultra and Liberty, allow the addition of ammonium sulfate, while others require a crop-oil concentrate or nonionic surfactant plus an ammonium fertilizer adjuvant. Remember, do not apply postemergence herbicides in a liquid fertilizer carrier, as severe corn injury can occur.

Marshal McGlamery (mmcglame@uiuc. edu) and Aaron Hager (, Department of Crop Sciences, (217)333-4424