Issue No. 9, Article 8/May 21, 2004
Not Quite Out of the Woods
Corn planted on April 15 here at Urbana is on the V4 stage and about 8 inches tall. So far, the crop has emerged and developed much as predicted by the growing degree-day (GDD) method. As I wrote several weeks ago, the corn emerged at about 120 GDDs, just as expected. We have received about 320 GDDs since emergence, which is close to the 85 GDDs per leaf that are predicted based on work by Bob Nielsen at Purdue University and Peter Thomison at Ohio State University.
Having corn get to stage V4 by May 20 is favorable. If average or higher temperatures, and hence growth rates, persist over the next weeks, we will see tassels by the end of June. Keep in mind that with the accelerating pattern of GDD accumulation throughout June, a crop that is a week ahead of normal development now may be only about 3 days ahead of normal by the end of June. A fast-growing crop can "outgrow" a number of problems, and it will use more of the sunlight in coming weeks, but if cold temperatures return, a larger crop is more vulnerable to injury.
Despite a record early corn-planting season, heavy rains and temperature swings have many people wondering whether there's "trouble in paradise" regarding the corn crop. Make no mistake--the crop went in and emerged in most fields under very good conditions, and stands in most fields are as good as we could have expected. And we have to admit to the old truism that when things are in good shape, small problems become larger problems, at least in our minds. But there are a few problems that we should look for as the crop gets started.
The first and most immediate problem in some fields or parts of fields is standing water. Though we have had enough dry weather to make the soil able to absorb an inch or two of rainfall in many fields, excess rainfall, or rain that comes very fast, will still run off and form ponds, or creeks will rise to cover fields. Larger plants have more leaf area that stays above the water level better and emerges from submergence sooner, and they can survive submergence longer than can small plants. By the time it dries off enough to consider replanting, plants should be showing substantial new growth. With warm temperatures, in fact, growth should resume within 2 days or so of the water's subsiding.
If new leaf tissue does not appear, or if it appears slowly, pull some plants and cut them open to see whether the growing point (the small triangle of stem tissue to which leaves are attached) is white and healthy looking. If it is, there's a chance that the plants may resume growth without much lasting damage. If there is any discoloration, the plant may die or fail to recover to full health.
Complicating this is the fact that roots that remain in saturated soil cannot support growth very well, diseases like crazy top might have infected the plants during submergence, leaves may have mud on them, and nitrogen loss can be substantial. It is difficult to predict, but sometimes a crop that has been submerged simply fails to grow back very well, even when soils dry again and the sun shines.
Another problem in Indiana that Bob Nielsen has written about, and about which we have gotten a few reports in the past week, is abnormal seedling growth, often including leafing-out underground in scattered plants. This problem appears on some hybrids more than others and seems to occur more in fields planted within certain time periodsone field might be affected, while the same hybrid in fields planted a few days earlier or later shows none of the problem.
I'm going to speculate here, but when seeds planted into relatively warm soil experience a temperature drop (as has happened at least twice within the past month), the coleoptile experiences the lower temperatures first, and its growth may slow. But the new leaf inside it, "pushed" by the warmer seed deeper in the soil, continues to grow, eventually breaking out even though the coleoptile has not broken the soil surface. Coleoptile growth is usually stopped by sunlight hitting its tip, but anything that slows its growth, including some herbicides, can result in premature release of the leaf. If this theory holds, then hybrids that tend to have vigorous early growth might be the ones most affected.
Soybean planting has been rapid, with 57% of the state's crop planted as of May 16. That's much better than in recent years, but rainfall has stopped progress in many locations, and it could be a week before planting resumes in many areas. Our data show very slow declines in yield as planting approaches the end of May, so we still have time to plant with little yield penalty. Of course, that all depends on weather later in the season, especially in August.
To see this, we need only look back at the past 2 years, both of which had delays in getting soybean planted. In 2002, we had good yields following late planting; in 2003, especially where it rained little in August, we did not have good yields. One additional concern is wet fields where soybean has been planted. With warm soils, soybean seed can tolerate flooded or saturated soils for only a few days. Watch fields, especially lower parts of fields with standing water, and line up replanting seed as you wait for soils to dry.
I saw a field near St. Elmo this past week where field pea had been no-tilled into corn stalks around March 20. The field was virtually devoid of plants; I could not see any planted from the road, but someone who had seen the field more closely said there was a small area out in the field with some stand. While the spring has been cool and dry enough in general to be considered relatively good for a crop like pea, the heavy rainfall event soon after planting must have been too much for the seeds or seedlings trying to emerge. I hope that fields in other places look better. If you have seen fields of this new crop up and growing, I would appreciate an e-mail on the condition of the crop.
Wheat continues to develop ahead of schedule, from a few days ahead in southern Illinois to more than a week ahead in the northern part of the state. Much of the crop escaped rainfall during flowering, so Fusarium head scab may not be as big a concern as it was last year. Color of the crop is generally good, though the return of wet conditions, accompanied by high temperatures, will not be ideal as the crop fills grain. By now, it is too late to do much about crop condition, except to hope for cool, dry weather to maximize the rate and duration of grain filling.--Emerson Nafziger