Restrictions on Corn Height for Postemergence Applications

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

A lot of the early planted corn needs to be scouted to determine if you are having weed emergence. The corn throughout the state is growing slowly and is nowhere near the stage it typically is in late May. So there will be a number of considerations for postemergence herbicide applications. In general, early emerging weeds are a bigger issue than late emerging weeds because they cause more yield loss, tend to get taller and larger, which causes more problems at harvest, and they produce more seeds. The following table was developed to help making these decisions. If tankmixing herbicides, follow the most restrictive label. The addition of atrazine will improve performance of many of the following herbicides (in particular Callisto, Halex GT, Laudis, Capreno, Impact, or Armezon).

This table is only for comparison of selected herbicides, be sure to read and follow all labels.

Herbicide Constituent Products Broadcast Application/
Drop nozzles
Comments
2,4­D <8 inches tall /

Drop nozzles up to 36”

Some 2,4­D formulations allow application up to tasseling.

Limited to no residual control

Accent Q 20 inches tall (free­standing) or <6 collars (V6 stage) /

Drop nozzles up to 36” or V10 stage

Limited to no residual control
Aim Up to 8­leaf collar stage (V8) /

Drop nozzles up to V14 stage

Excellent for velvetleaf, but other species must be small for effective control.

No residual control

Atrazine 12 inches tall Residual control depends on rate – generally fair to good residual control
Banvel or Clarity dicamba 1 pt: 8 inches tall or 5 leaves

0.5 pt: 8–36 inches tall or 15 days before tassel emergence

Do not apply Banvel or Clarity near soybeans if corn is >24 inches tall, or if soybeans are >10 inches tall or have begun to bloom.

Limited to no residual control

Cadet Up to 48 inches tall /

Drop nozzles are permitted before tasseling

Excellent for velvetleaf, but other species must be small for effective control.

No residual control

Callisto,

Callisto GT

 

Callisto + glyphosate

Up to 30 inches tall (or 8­-corn leaf stage) Improved control with the addition of atrazine.

Residual control depends on rate – generally fair to good residual control

Capreno Laudis + thiencarbazone Up to V6 (6 collars)

Drop nozzles up to V7 stage

Improved control with the addition of atrazine.

Limited residual control

DiFlexx dicamba + safener Up to 36 inches tall (V6 stage) /

Drop nozzles up to V10 stage

Limited to no residual control
Glyphosate products Up to 30 inches tall (V8 stage) Apply to Roundup Ready hybrids only

No residual control

Halex GT Dual + Callisto + glyphosate Emergence to 30 inches tall (8­leaf stage) Improved control with the addition of atrazine.

Residual control depends on rate – generally good residual control

Impact or Armezon Up to 45 days prior to corn harvest /

Drop nozzles are permitted

Improved control with the addition of atrazine.

Limited residual control

Laudis Emergence up to V8 stage Improved control with the addition of atrazine.

Limited residual control

Liberty 280 Emergence to V5 (5 developed collars)

Up to 36” tall

Apply to Liberty Link or GR corn hybrids only.

No residual control

Realm Q Resolve + Callisto Up to 20 inches tall but with no more than 6 collars Residual control depends on rate – generally fair to good residual control
Roundup products Up to 30 inches tall (V8 stage) Apply to Roundup Ready hybrids only

No residual control

Status dicamba + difluenzapyr + safener 4–36 inches tall (V2–V10) Do not apply within 15 days before tassel emergence

Limited to no residual control

Steadfast Q Accent + Resolve Up to 20 inches tall (6 collars) Best if applied when corn is <12 inches tall

Generally fair to good residual control

Touchdown Emergence through V8 stage Apply to Roundup Ready hybrids only.

No residual control

Yukon Permit + dicamba Spike to 36 inches tall /

Drop nozzles are permitted

Residual control is fair to good on limited species