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Issue No. 11, Article 7/June 4, 2004

Do You Need to Replant?

Almost every location in Illinois reported above-normal rainfall for the month of May, with more than double the normal amounts in some locations. This occurred in many areas in 2003, as well, with some replanting of both corn and soybean in some places last year. In comparison, the planting progress for both crops was much better this year, and much of the corn is large enough that damage from excessive water is less severe this year. Of course, larger corn also hides problem areas better, so we can't assume that the corn is in great shape across every field just because it looks good from the road.

Except where water stood on fields of smaller corn or in low areas long enough to kill larger corn, or where hail killed plants, it is not likely that much corn will be, or should be, replanted. Based on planting date studies, we expect that corn planted in early June will yield about 75% of corn planted in late April, but we know that this number will vary considerably, depending on the weather during the summer. Replanting corn in June requires consideration of hybrid maturity, given the shorter growing season left to work with. Work at Purdue and Ohio State confirmed that late-planted corn doesn't need as many growing degree-days as corn planted earlier, when temperatures are cooler. As I've said before, the reduction in GDD requirement is directly related to the reduction in yield potential for late-planted corn.

For most of Illinois, that means that we should not be quick to change corn hybrid maturities for planting in early June. In central and southern Illinois, unless the first choice is to plant very full-season hybrids, maturity should probably not be changed for late planting. Remember that hybrids more than 6 or 7 days (relative maturity) earlier than midseason hybrids for an area were not developed for general use in that area, so many have unexpected disease problems.

Soybean has been hurt by water and hail much worse than corn--due to its later planting, earlier development stage, and growth habit. There have been some reports of hail damage resulting in soybean plants that do not grow back. This could be due to diseases that move in after damage; but when both cotyledons and the growing point are broken, the part of the plant left alive has no meristem tissue able to resume development of plant parts. Without new leaves or stems, what's left of the plant often dies. Especially if there is still some green leaf area on such plants, the plants may accumulate sugars in the stem tissue (such sugars have no place else to go), and stems may swell and become brittle. Such fields may need replanting.

Standing water is a more widespread problem in soybean, and it is clear that some fields, and parts of some fields, will need to be replanted or repair-planted. Yield potential for soybean planted in early June should still be 80% or more of full-season soybean, so replanting should be considered if crop conditions continue to deteriorate. Be sure to wait until fields are ready to replant, at least a few days after it's dried off enough to walk on the field. Repair planting with less than a full seeding rate to fill in those areas with some stand may be appropriate, as long as the initial stand does not have more than two or three leaves, or is damaged enough so it has to grow back as the new crop emerges. Do not change to earlier soybean varieties when planting is delayed. They will often make less than adequate vegetative growth for top yield. By the same token, any soybean planting after June 1 should be in narrow rows, 15 inches or less apart. This will make a better canopy in case it turns dry and vegetative growth slows.

The story is almost complete on the wheat crop for 2004. Heavy rains have hampered grain fill, and Fusarium head blight (scab) has heavily infected some fields in the northern half of the state. Sunny days with moderate temperatures like we're having this week will help some, but the best we can hope for is complete fill of the kernels that are in the fields now. That will not be adequate to give yields like we had in 2003, but the crop could still be better than average.--Emerson Nafziger

Emerson Nafziger

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