No. 7 Article 5/May 20, 2011

Can Soil-Residual Corn Herbicides Be Applied After Corn Emergence?

Corn planting progress accelerated in much of Illinois in the past week. Some fields may have been planted before a planned soil-residual herbicide was applied. If the corn has not yet emerged, the application could proceed as planned. But if the corn has begun to emerge, can the soil-residual herbicide still be applied, or will a different product be needed? The answer depends on the herbicide. Many, but not all, herbicides that are most frequently applied before corn planting or emergence can be applied after the corn has emerged.

Even if a soil-residual herbicide can be applied after crop and weed emergence, not all soil-residual herbicides will control emerged weeds, so additional management procedures (such as adding a herbicide with postemergence activity) may be needed in situations where weeds also have emerged. Table 1 summarizes information about postemergence applications of the more traditional soil-applied corn herbicides. Please consult product labels for additional information, such as the need for tank-mix partners or spray additives to improve control of existing weeds.

Table 1. Maximum corn size for postemergence applications of soil-residual herbicides.

Herbicide

Maximum corn size for broadcast application

Comments

Prequel

Apply before emergence

Do not apply to emerged corn.

Princep

Apply before emergence

Will not control emerged weeds.

Verdict

Apply before emergence

Do not apply to emerged corn.

Python WDG

2 in.

Apply before first corn leaf unfurls.

Balance Flexx, Corvus

2 leaf collars

Do not add COC or MSO after corn emergence.

Micro-Tech

5 in.

Will not control emerged weeds.

Bullet

5 in.

Will provide control or partial control of small (<2 leaves) broadleaf and grass weed species.

Cinch ATZ, Cinch ATZ Lite, Stalwart Xtra, Parallel Plusa

5 in.

Will provide control or partial control of small (<2 leaves) broadleaf and grass weed species.

FieldMaster

11 in.

Apply postemergence only to glyphosate-resistant corn hybrids.

Surpass, TopNotch, FulTime, Harness, Harness Xtra, Degree, Degree Xtra, Keystone, Keystone LA, Breakfree, Breakfree ATZ, Breakfree ATZ Lite

11 in.

Surpass, TopNotch, Harness, Breakfree, and Degree will not control emerged weeds.

SureStart/TripleFLEX

11 in.

Will provide control or partial control of certain small (<1.5") broadleaf weed species.

Atrazine

12 in.

Add COC if weeds have emerged.

Bicep II Magnum, Bicep Lite II Magnum

12 in.

Will provide control or partial control of small (<2 leaves) broadleaf and grass weed species.

Expert

12 in.

Apply postemergence only to glyphosate-resistant corn hybrids.

Guardsman Max, G-Max Lite

12 in.

Will provide control or partial control of small (<1.5") broadleaf and grass weed species.

Lumax, Lexar

12 in.

NIS or COC may be added for postemergence applications.

Outlook

12 in.b

Will not control emerged weeds.

Resolve DF

12 in. (V5)

Apply before grass weeds exceed 2 in. and broadleaves exceed 3 in.

Hornet WDG

20 in. (V6)c

Postemergence applications must include NIS, COC, or MSO.

Resolve Q

20 in. (V6)

Apply before grass weeds exceed 2 in. and broadleaves exceed 3 in.

Callisto

30 in. (V8)

Postemergence applications should include a COC and nitrogen fertilizer.

Camix

30 in.d (V8)

NIS or COC may be added for postemergence applications.

Prowl H2O

30 in. (V8)

Will not control emerged weeds.

Dual II Magnum, Cinch, Me-Too-Lachlor II, Stalwart C, Parallel

40 in.

Will not control emerged weeds.

TriCor

Apply before tassel emergence

Do not add COC or POC.

aAll of these herbicides are labeled for directed applications to corn up to 12 in. tall.
bOutlook is labeled for layby application to corn up to 36 inch tall.
cHornet is labeled for directed application to corn up to 36 in. tall.
dApplications to corn greater than 12 in. tall should be post-directed.

Farmers are also cautioned about the potential for enhanced corn injury if these products are applied during periods of crop stress, such as that caused by excessive soil moisture or cool air or soil temperatures. Depending on the herbicide, tank-mixing other products or including various types of spray additives may be necessary to control existing weeds, but this may also increase the potential for corn injury. Attempting to save a trip across the field by applying a herbicide with a liquid nitrogen fertilizer solution (such as 28% UAN) as the carrier is not advisable if the corn has emerged.

Whatever the scenario, always remember that soil-residual herbicides need to be moved into the soil solution to be available for uptake by weed seedlings. A herbicide that remains on the soil surface after application and is not moved into the soil profile by precipitation or mechanical incorporation may not provide adequate residual weed control.--Aaron Hager

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