Continued wet weather throughout southern Indiana this second week of June has almost put an end to the opportunity for finishing up planting of intended corn acres. Let's look at a few issues of interest.
Because of different climatic patterns, southcentral and southeast Indiana corn farmers should consider "pulling the plug" on corn planting by about June 24, while southwest Indiana corn planting can continue through about the end of June. While either situation seems awfully late to be planting corn, two factors play into this opportunity.
First of all, typical "full season" hybrid maturities planted throughout southern Indiana commonly use far less than the available season-long accumulation of growing degree days (GDD). This fact is why little maturity switching has been necessary for plantings to date. Secondly, research from Purdue and Ohio State universities (see P&C, May 8, " Don't Pull the Trigger Yet on Hybrid Maturities") suggests that corn hybrids' GDD needs lessen as planting dates are delayed. Extrapolation of those results to this year's situation are illustrated in Table 1.
For the time period June 17 - 23, corn planting can continue throughout southern Indiana using hybrid maturities that are earlier than usually planted. Careful consideration should be given to selecting earlier maturities that have strong disease tolerance/resistance ratings. Because of the risk of such late-planted fields being attractive to European corn borer infestation, the extra cost of early-maturity Bt hybrids would be worth the "insurance premium".
For the time period June 24 - 30, extremely early maturity corn hybrids (relative to the region) could still be planted, but be very particular about the disease tolerance characteristics of the available hybrids. As noted earlier, the extra cost of early-maturity Bt hybrids would be worth the "insurance premium" if they are available AND have good disease tolerance.
Note on Planting Rates: Do not make major adjustments to your usual planting rates. Delayed planting of corn, especially using shorter-statured early maturities, requires fairly aggressive populations to ensure complete canopy closure prior to pollination.
|Table 1. Approximate safe hybrid
relative maturities for several planting date periods throughout
|Southwest||June 17 - 23||112|
|June 24 - 30||106|
|Southcentral||June 17 - 23||104|
|June 24 - 30||99|
|Southeast||June 17 - 23||104|
|June 24 - 30||99|
Disclaimer to Table 1: Be aware that there are no agreed upon standards within the seed industry for assigning relative hybrid maturities. The hybrid CRMs listed in Table 1 correspond most closely to those used by Pioneer Hi-Bred Int'l, Inc. Given Pioneer's large market share in seed corn, almost every other seed corn company can likely tell you which of their hybrid maturities correspond to Pioneer hybrids with the CRMs listed in Table 1.
Given the late date, do not waste the time and effort of applying starter fertilizer to corn. If the planting window opens in the next week or two, all of your time should be devoted to planting seed. The soils are warm enough for rapid corn germination and development, plus soil nitrogen has begun to increase due to the onset of N mineralization. Similarly, do not use valuable planting time to apply pre-plant nitrogen or other nutrients. Instead, plan on side-dressing nitrogen later after the corn has emerged.
Nitrogen application rates should be adjusted downward to account for the reduced yield potential of corn planted this late in the season. Estimate corn yield potential using a "1.5 bushels per acre per day after May 10" rule of thumb plus your own experience in recent years where planting was similarly delayed. As an example, a field that would "normally" yield 140 bushels if planted in late April might yield only 80 bushels if planted about June 20 (forty days after May 10 times 1.5 bushels per day). Such a yield potential would require no more than 80 pounds of available nitrogen.
What little corn was planted earlier throughout the region may not be the most uniform-looking fields ever seen and/or plant populations may be low or uneven. At this late date, think twice (or more) about replanting ugly fields. Even half a stand of reasonably healthy plants will likely have the same yield potential or greater of a full stand replanted in the next week or so.