Delayed Soil-Applied Herbicide Application

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

With all the rain recently, there is a lot of corn that has been planted, but has not been sprayed yet. First of all, do not panic and try to rush out and spray before the ground has a chance to dry out a little. If it is Roundup Ready or Liberty Link corn, then consider tankmixing your residual herbicide with glyphosate or Ignite. Most residual herbicides can be applied to emerged corn. However, there are restrictions on how tall the corn can be at time of application (see table below).

With conventional corn, the approach is similar. But you need to be sure you use a product that will control the emerged weeds in your field. Most of the residual products have atrazine in them, but depending on your rate, the atrazine rate may not be high enough. Hornet or Lumax or Lexar all contain active ingredients that will control a range of broadleaf weeds and are good choices to provide control of emerged weeds and provide residual control. For emerged grasses, a product with rimsulfuron or including Impact or Laudis may be needed depending on the grass species present (rimsulfuron is weak on crabgrass and Impact or Laudis are weak on fall panicum). Remember, Dual, Lasso, acetochlor products, or Prowl will not control weeds after they have emerged. 

Corn Height Restrictions for Postemergence Herbicide Applications

Herbicide

Maximum Corn Height

Atrazine

12 inches

Callisto

30 inches or 8 leaf

Define

5 collar

Dual II Magnum / Cinch

5 inches

Lasso

5 inches

MicroTech

5 inches

Outlook

12 inches

Princep

do not apply to emerged corn

Python

20 inches or 6 collars

Prowl / Prowl H2O1

30″ or 8 collar, whichever is more restrictive

Topnotch / Harness / Degree / Breakfree

11 inches

Premixes

Basis

no later than 2 collars

Bicep II Magnum 2 / Cinch ATZ2

5 inches

Bicep Lite II Magnum2

5 inches

Bullet2

5 inches

Field Master2

not labeled for emerged corn

Fultime2 / Keystone2 / Breakfree ATZ2

11 inches

Guardsman Max2

12 inches

Harness Xtra2 / Degree Xtra2

11 inches

Hornet WDG

20 inches

Lexar2

12 inches

Lumax2

12 inches

Sequence (RR corn only)

30 inches

SureStart

11 inches

1Refer to label of other pendimethalin formulations to determine restrictions on corn size

2This product contains atrazine. Use of a non-ionic surfactant or crop oil concentrate with atrazine (or its pre-mixed products) will increase weed control, but also increases the likelihood of corn leaf burn.

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