With the warm temperatures and recent rainfall across Wisconsin, winter annuals and early summer annual weeds are growing aggressively. As a result, many growers and retailers are revisiting burndown programs ahead of corn planting and asking an important question:

“Can I apply dicamba before planting corn, and if so, how long do I need to wait before planting?”

Unfortunately, the answer is not always straightforward.

Unlike 2,4-D labels, which often contain clear and explicit planting intervals ahead of corn, dicamba labels vary considerably depending on:

• Product formulation
• Tillage system
• Soil texture and organic matter
• Application timing
• Whether the product is labeled for true PREPLANT use or only PREEMERGENCE use

This creates confusion because university publications, historical recommendations, and individual product labels may appear to conflict.

First Key Point: Corn Is More Sensitive to 2,4-D Than Dicamba

One reason dicamba labels can appear less restrictive than 2,4-D labels is that corn generally tolerates dicamba better than 2,4-D.

With dicamba, the primary concerns ahead of corn planting are usually:

• Direct seed or seedling exposure
• Herbicide concentration in the seed furrow
• Injury under coarse-textured or low organic matter soils

rather than a traditional “rotational crop interval.

That is why many dicamba labels emphasize:

• Soil texture restrictions
• Organic matter restrictions
• Tillage system
• Avoiding herbicide concentration over the seed furrow

instead of providing a simple “wait X days before planting” statement.

Why the Confusion Exists

Some university resources still reference older guidance such as:

“8 oz dicamba = 7-day wait before corn planting”

However, many modern dicamba labels do not actually include a universal waiting interval for corn.

Instead, the label language is often tied to:

• Whether the application occurs in no-till vs. tilled systems
• Whether corn is already planted
• Whether the application is classified as PREPLANT or PREEMERGENCE

As a result, growers should avoid relying on generalized dicamba recommendations and instead interpret the specific product label carefully.

Decision Tree: Preplant Dicamba Ahead of Corn

STEP 1 : What tillage system are you using?

A) NO-TILL CORN
Many dicamba products, including older formulations such as Banvel, Clarity, and Sterling Blue allow PREPLANT applications in no-till corn. In these systems, emerged weeds are present and dicamba is commonly used as part of a burndown program before or around planting.

Key considerations:

• Follow soil texture and organic matter restrictions
• Avoid direct seed exposure
• Follow labeled application rates

For example, Banvel, Clarity, and Sterling Blue specifically allow:

• PREPLANT and PREEMERGENCE use in no-tillage corn
• Applications before, during, or after planting in no-tillage corn

when used according to soil restrictions.

An additional practical consideration in no-till systems is planter setup and furrow closure. Injury risk can increase when corn is planted into wet conditions and seed furrows later reopen as soils dry. Subsequent rainfall can move dicamba into the seed furrow, increasing the likelihood of seedling exposure and crop injury. Proper planting depth and effective furrow closure are therefore important risk-management practices when using dicamba ahead of corn in no-till systems.

B) CONVENTIONAL OR REDUCED TILLAGE CORN
This is where label interpretation becomes much more restrictive.

Many older dicamba products do NOT clearly support PREPLANT applications ahead of tilled corn.

Instead, labels often specify:

• PREEMERGENCE applications
• Applications AFTER planting but BEFORE corn emergence

This distinction matters.
If a label discusses only PREEMERGENCE use in tilled systems, growers should avoid assuming that a true PREPLANT burndown application is automatically allowed.

Product Comparison: More Restrictive vs. More Flexible Labels

More Restrictive Labels (e.g. Sterling Blue, Banvel, Clarity)

These products are generally:

• More restrictive ahead of tilled corn
• More dependent on soil restrictions
• More cautious regarding seed exposure

Example:
Sterling Blue / Banvel / Clarity label language:

• Allows PREPLANT in NO-TILL corn
• Allows PREEMERGENCE in conventional/reduced tillage corn
• Does not clearly describe PREPLANT applications ahead of tilled corn

Practical implication:
If applying ahead of tilled corn before planting, caution is warranted because the use pattern may not be explicitly supported.

More Flexible Label: Diflexx

Diflexx labels are generally more flexible regarding:

• Tillage systems
• PREPLANT uses
• Application timing ahead of corn

Diflexx also contains a safener (cyprosulfamide) designed to help corn metabolize dicamba more effectively.

However, even with Diflexx:

• Avoid direct seed contact
• Avoid concentrating herbicide into the seed furrow
• Follow soil and placement precautions carefully

The safener reduces crop response risk, but it does not eliminate injury potential under poor placement or adverse conditions.

Practical Extension Recommendations

When discussing dicamba ahead of corn, the following principles are useful:

1. Follow the specific product label

Avoid generalized “dicamba rules.” Labels differ substantially among formulations.

2. Distinguish between PREPLANT and PREEMERGENCE

This is especially important in conventional or reduced tillage systems.

3. Pay close attention to soil restrictions

Many dicamba labels become more restrictive on:

• Coarse soils
• Low organic matter soils

4. Avoid herbicide concentration in the seed furrow

Tillage or planter movement can concentrate treated soil around the seed and increase injury risk.

5. Prefer products with clearer PREPLANT flexibility in tilled systems

If a true preplant burndown is desired ahead of tilled corn, products such as Diflexx generally provide clearer label support than older dicamba formulations.

Bottom Line

For preplant dicamba ahead of corn:

• NO-TILL systems generally offer greater flexibility
• TILLED systems require more careful label interpretation
• Older dicamba products (Banvel/Clarity/Sterling Blue) tend to be more restrictive ahead of tilled corn
• Diflexx provides a more flexible label for PREPLANT use
• Most concerns relate to seedling exposure and placement rather than rotational interval restrictions

As always, the label remains the final authority.

Acknowledgements: The author would like to thank Mr. Dave Welsh and Dr. Vince Davis for reviewing this article and providing valuable input and discussion regarding dicamba use patterns ahead of corn planting.

Article written by Dr. Rodrigo Werle, UW-Madison Extension Cropping Systems Weed Scientist.