Indiana Corn: How Late Is “Too Late” to Plant? Key Points to Consider.

Corn planting. Photo: University of Minnesota

As May transitions to June, many Indiana corn growers are faced with substantial acreage yet to plant. Statewide, as of May 26, only 22% of the state’s corn crop was estimated to have been planted.

That disappointing planting progress positions the 2019 planting season at the moment just slightly ahead of the similarly slow 1996, which currently holds the unenviable record for the most delayed planting season in the past 40 years. And, there is still a chance we will surpass (or should I say “fall behind”?) that record by the time this planting season is finished.

In the remaining days of May, thunderstorms continued to rumble across the state… sometimes across the north… sometimes across the south… sometimes through the central counties. Unless a rapid shift from rainy to sunny, warm, and windy occurs soon, the prospects of serious planting progress through the first week of June are dismal.

The question of how late is “too late” to continue trying to plant corn is not an easy one to ponder. Physiologically, we could plant corn anywhere in Indiana through at least the end of June and still safely mature the crop before an average date of a killing fall freeze.

Success in doing so relies heavily on the choice of RELATIVE HYBRID MATURITY and that choice relies heavily on the availability of hybrids with Growing Degree Day (GDD) requirements suitable for the estimated number of GDDs between the end of June and the average date of a killing fall freeze.

At some late planting date, however, the “safe” relative hybrid maturities would be so unadapted to Indiana growing conditions that it would be foolish to plant them. Practically speaking, hybrids rated no less than about 2400 GDDs to kernel blacklayer, roughly equivalent to “100-102 day” relative maturity (reasonably adapted to Indiana growing conditions), could be safely planted in the northern tier of Indiana counties through June 15.

However, I would strongly encourage you to make sure such hybrids have disease ratings for important foliar diseases like gray leaf spot and fast grain drydown characteristics.

Understand, though, selecting a hybrid maturity that just barely reaches physiological maturity before a killing fall freeze in mid- to late October will not have much opportunity for significant field drydown and so grain moisture at harvest will be high.

If you search for a hybrid maturity that will reach blacklayer by, say, the end of September, that would provide more time for meaningful grain drydown in the field before harvest.

Let’s use an example from northeast Indiana (Dekalb, Noble, LaGrange, Steuben counties) with an expected planting date of June 10 and a desired blacklayer date of Sept 30. The average number of GDDs available to a corn crop for that time period is about 2100.

Using the method for estimating the reduction in hybrid GDD ratings for late plantings described in my related article, you arrive at a hybrid GDD rating originally defined as 2400 GDDs, roughly equivalent to “100-102 day” relative maturity, that should mature by the end of September.

DISCLAIMER: The example of a 2400 GDD hybrid is not a broad rule of thumb. The process outlined my related article (here) will help you fine-tune these hybrid maturity estimates for your specific combination of location, expected planting date, and desired maturity date.

Other Late Planting Considerations:

There is little need to change SEEDING RATES for unusually late planting (Nielsen, 2019b). Certainly, I would never increase my seeding rate. I might, however, decrease it by a couple thousand seed if I believed that germination, emergence, and initial stand establishment would be more successful due to warmer soils in June than what we typically experience in late April.

The ECONOMIC OPTIMUM NITROGEN RATE for unusually late planted corn is essentially the same as for earlier planting, especially if your typical nitrogen (N) program involves application near planting or in a sidedress operation.

However, if you normally apply fall anhydrous ammonia or apply nitrogen early in the spring (late March – early April), then you might be able to decrease your “usual” N rate by 20 to 30 lbs N to account for the fact that N applied closer to the crop’s need has a lower risk for N loss than much earlier applied N.

Corn yield response to STARTER FERTILIZER is admittedly inconsistent and not necessarily correlated with early or late plantings, or with tillage system. Based on 30 field scale trials conducted in the past several years, my colleague Jim Camberato and I have observed increased yields due to row starter about 33% of the time.

If you normally use starter fertilizer at planting AND if eliminating that from your planting process will significantly increase the number of acres you can plant per hour AND if you believe that you need all the acres per hour you can squeeze out of the planting operation… Then you can eliminate the starter fertilizer with minimal risk of lower yields.

Recognize, however, that grain moisture response to row starter (2×2) is more consistent and grain moisture is often 1 to 2 points drier at harvest. If this is economically important to you AND the time savings from not using starter fertilizer is not significant, then don’t eliminate it from your late planting.

How’s that for wishy-washy advice?

The typical REDUCTION IN YIELD potential due to LATE PLANTING ranges from 1 to 2 bushels/acre/day delay after about May 10 to 15. That is certainly a consideration when you are debating whether to switch from planting corn to planting soybean in early June or opt for the Prevented Plant option of your crop insurance policy.

However, recognize that this estimate of reduced yield with delayed planting does not tell you what the actual yield will be for that late planted corn field. If the remainder of this season turns out to be picture perfect, then yields may end up surprisingly high… It’s just that they could have been even higher if the corn could have been planted earlier in good conditions.

If the remainder of this season continues its path down the proverbial toilet, then yields will be dismal… And, yes, the yield might have been higher if the corn could have been planted earlier in good conditions.

IF, IF, IF……… To me, this conundrum is the “devil in the details” when it comes to penciling out the comparisons of switching to soybean or opting for the Prevented Plant provision of crop insurance.

Last fall’s wet weather prevented a lot of post-harvest TILLAGE around the state. Certainly, the wet weather this spring has prevented a lot of pre-plant tillage. The seemingly incessant rainfall events continue to delay significant drying of the soils.

In a perfect world, one would tell you to eliminate tillage at this point on the calendar and focus on planting once the fields dry out. The reality is that if your planting equipment and/or herbicide programs are not geared toward no-till practices, this is not a good time to experiment.

Nevertheless, consider no-tillage for corn following soybeans, especially if existing weed pressure in the fields is not out of control and there are no ruts from last fall’s harvest operations. Consult with your ag chemical retailer about changes to your herbicide program relevant to no-tillage.

For fields with SEVERE RUTS, fill and level them with shallow tillage, but avoid deeper tillage because soil moisture below the depth of the ruts will likely be too wet for tillage without creating compaction.

If you simply have to till fields before planting, try to minimize the number of trips across the field. Try to avoid tilling fields that are “on the wet side” in order to avoid creating compacted soil layers that will restrict crop roots later.

Obviously, CROP INSURANCE options are a key consideration to your decisions about planting corn well into June. Two excellent resources published within the past couple weeks include a recorded Webinar from Purdue’s Center for Commercial Ag (below) and summary of financial options from Univ. of Illinois’ farmdocDAILY website. Take time to view or read these two pieces of information and visit with your crop insurance agent.


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