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Issue No. 8, Article 7/May 13, 2005

Lessons from an Unusual Planting Season

The good news is that corn planting in Illinois in 2005 has been record-early, with 94% planted by May 8 this year compared with 93% on the same date in 2004. In 2004, 63% of the crop had emerged by May 8, compared with 52% of the crop emerged this year. With the return of warm temperatures this week, much of the rest of the crop will emerge, so we should be getting back on track. In fact, the high temperature at Champaign was 90° on May 10, so it won't be long before the worry shifts from cold and wet to hot and dry. We have enough soil moisture to hold off that worry for a few weeks at least.

The favorable planting progress this year doesn't tell the whole story, unfortunately. There has been a considerable amount of replanting in some places, though we don't expect the replanted acreage to be much larger than it has been in some other recent years. The main reason for replanting in east-central Illinois has been soil crusting, and the crop that was planted about 3 weeks ago, just before the heavy rainfall around April 20, has had a difficult time emerging. The rotary hoe has been widely used in this area but hasn't always been enough to get adequate stands. Corn planted 2 weeks ago is emerging about as quickly as corn planted 3 weeks ago, and it looks much more uniform, though we don't think that the slow and somewhat uneven emergence in some fields will have serious consequences for yield, as long as the final stand is adequate.

The damage caused by the low temperatures of the last week of April and the first few days of May has been the big story of this planting season, and while most decisions regarding replanting have already been made, it's useful to examine what happened and whether this means we should change our approach another year.

Here is a summary of information regarding freeze injury to corn in 2005:

  • Low temperatures really were low, with lows in the 20s recorded at 19 of 40 Illinois weather stations during the first week of May, including 20° at Mt. Carroll in northwestern Illinois. Another 9 stations reported lows of 30° to 32°, and the rest all had lows in the 30s. All of the stations reported low temperatures in the 30s the last week of April as well, with a few in the 20s. We'd never dare say this won't happen again, but having temperatures this low was truly unusual.
  • Almost all of the corn that was killed or that failed to regrow after the aboveground leaf area was killed was planted before the end of the first week of April.
  • While there were few reports of out-right death of the growing point, death of stem tissue occurred as far as 1/2 inch down from the soil surface. Such a small amount of tissue left alive can seldom support regrowth.
  • Corn planted shallowly was more likely to be injured than corn planted deeper. We normally would not plant corn deeper than 1.5 inches or so when planting in early April, so "shallow" planting was more the rule than the exception. Planting deeper than that carries its own risks, and I do not think that better survival of deeper-planted corn this year should change our approach for next year.
  • There is some uncertainty about why deeper-planted corn might have survived better and why certain injury patterns appeared in some fields. Some have reported that the crown (growing point) was located more shallowly as a result of shallower planting and so was more subject to direct freeze injury. This is not normal; in most cases, crown depth is set, usually at about 3/4 to 7/8 inch deep, when the coleoptile tip emerges above ground and gets a signal from sunlight. That usually means that crown depth is more or less independent of planting depth, at least within the normal range of planting depths. Of course, seed planted less than an inch deep cannot set the crown deeper than the seed, so plants can end up with shallow crowns. And we have sometimes seen shallow crowns when planting into very warm soils. It's possible, when growth is very rapid, that the time of day the plant emerges above ground affects how soon light strikes the coleoptile tip and thus affects how deep the crown gets set. Soils were warm during the first week of April, but emergence and growth were not so rapid that such differences would have been noticeable. Given the pattern of damage, though, I think it's possible that much of the difference in damage among fields and plants might have been because of small differences in time of emergence. Shallower planting would have emerged slightly earlier, as would some plants down the row. Hybrids that emerged or grew more rapidly would also have suffered more damage. Such differences would have been well within the normal range of emergence and early growth, making such a connection less obvious.
  • Even though low temperatures occurred widely, much of the early-planted corn along the Springfield-Jacksonville-Quincy line survived well. Most of the damage serious enough to require replanting was in or near the Lincoln to Macomb to Moline triangle, likely from the combination of early planting, more growth with warmer temperatures, and then low temperatures. North of I-80, there was less planting done that early, and the corn did not emerge or grow as fast, so there was less damage. As an example, the March 30 planting of the same hybrid in our planting date study was much more badly injured at Monmouth than at DeKalb.
  • It remains to be seen if the rough start to the season will have lasting effects on yield, but it's safe to say that the most critical periods for yield are still to come, in July and August. If the 2005 weather pattern is like that in 2003 and 2004, we can expect good yields.

Soybean planting was already well ahead of the pace in 2004 at the end of last week and is proceeding rapidly this week. Any concern about planting soybean seed into cold soil has evaporated, but the challenge that could come from heavy rainfall after planting remains. Some of the crop may also be planted this week into soils too dry to ensure emergence, so the quandary about whether to plant before or after an expected rain will affect some. It's more or less a coin toss, in large part because "expected" rains sometimes don't arrive on time or in the expected amount. If we knew that a gentle inch of warm rain would fall on a dry field just after planting, then we should probably plant. In reality, we have to weigh chances of not getting a stand because of heavy rainfall against the fact that our optimum planting window extends for a week or two yet in Illinois and against the cost of seed if we need to replant.

Wheat has not been damaged to any extent by the low temperatures over recent weeks, but its development has been delayed to slightly behind average. Dry weather is favorable in terms of limiting development of diseases, including Fusarium head scab, and in providing the sunlight the crop needs for best yields. On the other hand, the crop needs 6 to 8 inches of water to fill grain, so some rain is helpful. Our rule of thumb is that maturity follows heading by about 6 weeks. That would put harvest time close to normal, which will be a week or more later than in 2004. This will be speeded up if the weather turns warm but at the cost of some yield potential.--Emerson Nafziger

Emerson Nafziger

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