Delayed Pre-Emergence Herbicide Applications in Corn Require These Considerations

Farmers in much of Kansas are planting at a rapid pace following the recent rain. However, the speed of planting coupled with unusually windy conditions can potentially interfere with pre-emergence herbicide applications (Fig. 1). There are several things to consider when the planter ‘gets too far ahead’ of the sprayer and corn is emerged before pre-emergence herbicides can be applied to corn.

Fig. 1 Because of weather conditions this spring, planting may have gotten ahead of preemergence herbicide applications in corn. Photo by Sarah Lancaster, K-State Research and Extension.

Residual herbicides that prevent weed emergence are the foundation of any weed management program. Fortunately, many of the residual products that might be applied pre-emergence to corn can also be applied to small corn. These include:

  • Atrazine
  • Group 15 herbicides such as acetochlor (Harness, Warrant, others), dimethenamid-P (Outlook, others), pyroxasulfone (Zidua, others) and S-metolachlor (Dual, others)
  • Group 27 herbicides such as isoxaflutole (Balance Flexx, others) and mesotrione (Callisto, others); and
  • Premixes that contain various combinations of these products, such as Acuron, Anthem, Armezon PRO, Corvus, Lumax or Lexar, Resicore and SureStart II.

Do not apply products that contain flumioxazin (Valor, others) to emerged corn. Table 1 includes key information about some of these products, including the maximum growth stage at which the products can be applied and the amount of rainfall required for activation. Activation requirements could be especially important this year, because of the concerns that drier-than-normal conditions may continue throughout the summer.

Herbicides that control emerged weeds should also be considered. Many corn hybrids are resistant to glyphosate and/or glufosinate (Liberty, others), so these products can remain in the tank mix. Dicamba can also be applied to emerged corn. The rates of dicamba that can be applied to emerged corn depends on the size of the corn. For corn from the spike stage through 8 inches, apply up to the 0.5 pound per acre rate (reduce this to 0.25 pound per acre on coarse-textured soils). Apply up to the 0.25 pound per acre rate until the corn is 36 inches or until 15 days before corn tassels emerge, whichever is earlier.

However, other products that are often included in pre-emergence applications to control emerged weeds cannot be safely applied to emerged corn. These products include paraquat (Gramoxone, others), saflufencail (Sharpen) and tiafenacil (Reviton).

Be sure to include appropriate adjuvants when applying premixed herbicides to emerged weeds. Consider using more “aggressive” adjuvants, such as COC or MSO, in dry conditions because emerged weeds will likely be more difficult to control. However, be aware that this decision also increases the risk of crop injury. Recommended adjuvants are listed in Table 1. When planning tank mixes, always check the herbicide label to clarify tank mix partners, other crop size restrictions and adjuvants for the tank mix.

Table 1. Key information for selected herbicides that can be applied post-emergence to corn

Example Product

Active Ingredient(s)

SOA group(s)

Water for Activation

Growth Stage

adjuvant

Aatrex 4L

atrazine

5

Sufficient

Up to 12”

(COC)

Status

diflufenzopyr

dicamba

19

4

N / A

4” (V2) to 36” (V8)

COC or MSO or NIS and AMS or UAN

Harness

acetochlor

15

¼ to ¾”

Up to 11” to 30” (only Warrant can be applied up to 30”)

Not required

Outlook

dimethenamid-P

15

needed

Up to 12”

Not required

Zidua

pyroxasulfone

15

½”

Up to V8

Not required

Dual II Magnum

S-metolachlor

15

½ to 1”

Up to 40”

Not required

Scale Flexx

isoxaflutole

27

Adequate

Up to V2

Not advised

Callisto

mesotrione

27

¼”

Up to 30” or V8 (whichever is more restrictive

COC or NIS (more consistent control with COC)

Acuron

S-metolachlor

atrazine

15

5

½ to 1”

Up to 12”

NIS or COC or AMS

Anthem MXX

mesotrione

bicyclopyrone

pyroxasulfone

fluthiacet-methyl

27

27

15

14

½”

Up to V4

NIS or COC

Armezon PRO

dimethenamid-P

topramezone

15

27

Required

V8 gold 30”

NIS or MSO

Corvus

thiencarbazone

isoxaflutole

S-metolachlor

2

27

15

Adequate

Up to V2

Not advised

Lumax

atrazine

mesotrione

acetochlor

5

27

15

½ to 1”

Up to 12”

NIS or COC

Resicore

mesotrione

clopyralid

acetochlor

27

4

15

¼”

Up to 11”

NIS or COC

SureStart II

flumetsulam

clopyralid

2

4

¼”

Up to 11”

Not required

For more detailed information, see the “2022 Chemical Weed Control for Field Crops, Pastures and Noncropland” guide available online at https://www.bookstore.ksre.ksu.edu/pubs/CHEMWEEDGUIDE.pdf or check with your local K- State Research and Extension office for a paper copy. The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.

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