By Aaron Hager, Extension Weed Scientist
The labels of most postemergence corn herbicides allow applications at various crop growth stages, but almost all product labels indicate a maximum growth stage beyond which broadcast applications should not be made, and a few even a state minimum growth stage before which applications should not be made.
These growth stages are usually indicated as a particular plant height or leaf stage; sometimes both of these are listed.
For product labels that indicate a specific corn height and growth state, be sure to follow the more restrictive of the two. Application restrictions exist for several reasons, but of particular importance is the increased likelihood of crop injury if applications are made outside a specified growth stage or range.
Maximum corn heights and growth stages:
Broadcast before corn exceeds 8” tall; use drop nozzles when corn is taller than 8”.
Broadcast up to 20” tall or through the V6 stage. Apply with drop nozzles when corn is 20–36” tall or before the V10 stage.
Apply from corn emergence through the V4 (visible fourth leaf collar) stage.
Apply from corn emergence to the 8-leaf stage or 30” tall.
Apply before corn exceeds 12” tall.
No height specified on label.
Apply to corn from spike through 2 collar stage. Do not apply to corn having 3 fully emerged collars or over 6” tall.
Broadcast when corn is 4–20” tall. After corn is 20” tall or exhibits more than 6 collars use directed applications up to tassel emergence.
Apply until corn is 48″ tall or prior to tasseling.
May be applied to corn up to 30” tall or up to the 8-leaf stage.
Apply before corn exceeds 12” tall
Broadcast applications must be made to corn from the 1-leaf collar stage through the 5-leaf collar (V5) stage.
Clarity or Banvel
Apply between corn emergence and the 5-leaf stage or 8” tall; apply 0.5 pt/A rate when corn is 8 to 36” or if 6th leaf is emerging, or if 15 days prior to tassel emergence. Do not apply when soybean are growing nearby if: 1) corn is more than 24” tall, 2) soybean are more than 10” tall, 3) soybean have begun to bloom.
Apply broadcast when corn is at the spike through 6-leaf collar (V6) growth stage, or 36” tall, whichever occurs first.
Glyphosate (glyphosate-resistant corn)
Apply broadcast through the V8 stage or until corn reaches 30” tall. Use drop nozzles for applications to corn 30–48” tall.
Halex GT (glyphosate-resistant corn)
Apply to corn up to 30″ tall or the 8-leaf stage.
Apply to 2–6 leaf corn with 1–5 collars or up to 16” tall.
Apply broadcast until corn reaches 20” tall or V6 stage. Apply with drop nozzles to corn up to 36” tall.
Can be applied up to 45 days before harvest. Do not apply Armezon past the V8 growth stage.
Apply up to the V8 growth stage.
Liberty (glufosinate-resistant corn)
Broadcast until corn is 24” in height or in the V7 growth stage (7 developed leaf collars). Use drop nozzles for corn 24–36” tall.
Apply between corn emergence and the 5-leaf or 8” height stage.
Apply prior to tassel emergence.
Broadcast applications are made when corn is between 4 –20” tall (V2–V6). Use directed applications when corn is 20–36” tall.
Can be applied from spike through layby.
May be broadcast applied to corn up to 20” tall or exhibiting 6 leaf collars.
Apply to corn 4–20” tall. Do not apply to corn exhibiting 7 or more leaf collars.
Do not apply to corn taller than 20” or exhibiting 7 or more leaf collars.
Apply to corn from the 2-leaf through 10-leaf stage.
Broadcast applications to corn up to 4 leaves or 8” tall; directed applications for 5-leaf or 8–11 ¾” tall corn.
May be applied broadcast up to the V8 growth stage or 30” tall.
Broadcast applications to corn 4–20” tall. Use drop nozzles when field corn is 20–24” tall or exhibits more than 6 collars (V6).
Apply broadcast to corn with up to 5 fully exposed leaf collars (V5).
Do not apply to corn taller than 36” or past the V10 stage.
Apply to corn up to 20” tall or exhibiting 6 leaf collars.
Apply to corn from emergence through 24” tall.
Apply broadcast or with drop nozzles to corn from spike to 36” tall. Drop nozzles are recommended when corn exceeds 20”.
May be applied after corn emergence until plants reach 30” tall or up to the V8 stage.