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Issue No. 8, Article 8/May 27, 2011

Getting to the End of Corn Planting

It's been a struggle this year, but as of May 22 we had 90% percent of the Illinois corn crop planted. Due to some luck dodging the rains over the weekend and up through May 24 in some places, that number will probably increase some this week. In areas that remain wet, it's possible that some acres intended for corn will be planted to soybean, or perhaps not planted at all. June 5 is the "prevented planting" date for Illinois except for a few counties in the southern tip of the state, where that date is May 31. It is not clear why the southern area has an earlier date, since we would expect the late planting penalty to increase at roughly equal rates by late May in different parts of the state, and we expect later fall frost in southern Illinois.

At the current price of corn, the prevented planting payment is unlikely to equal the income from a corn crop planted a week or more after that date, but net income will depend on how much has already been spent on the crop, and what insurance option was taken. Expected yield loss for a crop not planted until the end of May is 15% to 20%. This loss can be considered to include the possibility that the crop will not mature before frost, though that factor should likely move us toward the higher end of this loss range in northern Illinois.

The warm temperatures, including the warmer nights, in recent days have helped bring May growing degree-day accumulations back to near normal. At Urbana, we have accumulated more than 300 GDD since May 1 and more than 530 since April 1. Corn planted on or before May 18 has received enough GDD to emerge. Our corn planted at Urbana on March 31 is now at V5, and that planted on May 2 is at V3. While the early-planted corn plants are still small for their age, we expect them to start growing rapidly now, with stems beginning their elongation starting in about a week, at V6 to V7.

Though most planted corn has emerged reasonably well, there have been a number of reports of stand and plant damage. Planting conditions for the crop planted earlier in May were wetter than ideal in many fields, which could lead to earlier and more severe crusting. In most cases, though, rain has fallen before crusts can strengthen, and we don't see much "prevented" emergence. Cutworms and hail have removed a lot of the leaf area of young plants in some fields. In most cases this will grow back without too much problem, and if regrowth is early and healthy, little or no yield loss should result.

In fields where there was more severe hail or where there is damage from cool, wet soils, plant stands may well be lower than targets. Even if stands look good from the road, it pays to get into fields to count stands and see the plants. Most people who do stand counts measure off 1/1000 of an acre and count plants. That works well if it's done without selecting places to count, but it's easier to avoid bias when using the measuring wheel method. To do this, count 150 plants while pushing a measuring wheel, then note how many feet of row those plants occupied. For 30-inch rows, divide feet traveled (to count 150 plants) into the number 2,614 to get thousands of plants per acre.

Most fields have enough plants to rule out replanting by now, but some may not. Fields planted in April or early May with only 20,000 plants now will yield as much as a full stand planted at the end of May, as long as those 20,000 plants are healthy and uniformly spaced. Thus, while 20,000 plants may just look like too few to keep, the penalty for replanting this late is real, even if it's not as visible as a low stand.

If there is any replanting, the hybrid maturity used can be similar to that planted earlier, but if the planting is done as "repair"--only planting in areas of the stand within a field--it may be better to use a hybrid 5 to 8 days earlier than the first one planted so that harvest moisture between the early- and late-planted corn is more similar. Hybrids for fields still to be planted can, certainly for the next week or more, be those originally planned for use, especially in southern and central Illinois.--Emerson Nafziger

Emerson Nafziger

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