Many farmers face a replant decision after cool, wet weather impacted corn emergence and stand. In Southern Illinois, Josh Gunther, Burrus Hybrids product lead, says farmers haven’t had many windows to plant corn, if any.

As we approach June 1, here are 6 replant, or delayed planting, considerations:

1. Count’em up

In planted fields, Gunther recommends starting with a stand count. “You need to walk the entire field, take several stand counts and average them. If the average is below your stand goal, replanting may be a consideration,” Gunther says.

STILL TIME “According to the University of Illinois Agronomy Handbook, June 20-25th is the last practical day to plant corn,” says Josh Gunther, Burrus Hybrids. “Fields planted in this time frame can be expected to only reach 50% of the maximum yield.”

The objective is to calculate yield potential and determine the financial benefit of replanting; the yield gained from replanting must outweigh added input costs. Gunther recommends using this ‘Replanting Yield Projections’ chart as a guide.

The University of Illinois also offers an online tool for reference: Replant Decision Aid.  

2. Keep that hybrid...for now

Brent Tharp, Wyffels Hybrids agronomy and product training manager, recommends planting, or replanting, your original hybrid selection up to the end of May. “That hybrid was chosen for a good reason; because it best fits the geography, soil type, pest pressure and other factors in that field,” Tharp says. “The benefits of that placement outweigh any considerations of changing relative maturity.” Tharp explains that research indicates corn planted later adjusts and ‘catches up’ throughout the season.

3. When to swap hybrids

Tharp understands farmers’ concern, especially in northern Illinois, about planting a late-maturity hybrid past June 1. “Farmers are afraid it won’t finish, or black layer, before the first frost,” Tharp explains.

Growing Degree Days to black layer depends on hybrid genetics. Tharp says farmers should reach out to their seed representative for guidance on the best hybrid replacement, if needed.

Gunther notes farmers planting a mid-maturity hybrid for their zone, instead of a full-maturity hybrid, should be fine planting their original hybrid selection later in the season.

If a partial field is replanted, Tharp recommends selecting an earlier hybrid to keep harvest moisture similar throughout the field.

Gunther notes another hybrid swap factor to consider: later planted corn will grow taller, and place ears higher, due to warmer growing conditions during the stalk elongation phase. “What doesn’t change is the root structure, making a top-heavy corn plant more susceptible to lodging,” Gunter notes.

4. Clear the way

Tharp cautions against ‘spotting in’ low stand count areas. “Plants from two different planting dates will compete with each other,” Tharp explains. “It’s also difficult to know where to start planting and where to stop.”

Instead, Tharp recommends tillage, glyphosate or glufosinate, depending on the resistant trait in the existing stand, or post emergence herbicides to remove the current stand.

5. Factor in a Bt hybrid

Both Tharp and Gunther recommend switching to a Bt hybrid for replanted, or late planted, corn acres. “Replanted fields will be very attractive to a second generation of corn borer moths,” Tharp says.

“Late planted corn will flower later,” Gunther adds. “The pollen will attract the second, or even third, generation of moths.”

6. Ask questions

Farmers should contact their seed company regarding replant policies, replant decisions and hybrid selections. Your local seedsman or agronomist will help navigate the technicalities of another hybrid selection.