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Corn Planting Winds Down for Most

May 22, 2003

With what looks like a break (finally) in the wet weather pattern, many producers in the southern part of Illinois will at least get started on corn planting this week, and many people in other parts of the state will be able to finish up. We are fast approaching the time when producers tend to throw caution to the winds and get out and plant as long as the equipment doesn't get stuck or make tracks that are too deep. Last Friday I saw some planting getting under way in the northwestern part of Illinois, where rainfall has been very heavy. Most of the fields were in a condition that would have kept tractors out of the field if this were April and not approaching the end of May. I won't call that a "mistake" at this point, but if the weather pattern is favorable for more dry days ahead, an extra day or two of drying on marginal fields will probably be rewarded by a crop with better potential.

Planting into less-than-ideal conditions will work out if rainfall patterns are good for the whole season, but corn that is planted into soils that are too wet typically has a few strikes against it that can come back to hurt the crop if it undergoes stretches of dry weather later in the season. Such soils always have some level of compaction from equipment, including the planter units, that decreases air content and increases physical resistance to penetration by plant roots. This resistance may not impede roots if the soil stays moist and therefore softer, but the loss of pore space (air-holding capacity) will tend to decrease the successful proliferation of roots simply because they can't get oxygen fast enough.

If compacted soil dries out, physical resistance to penetration increases rapidly and will often "repel" roots wherever they encounter this barrier. This includes the planter opener track, where "sidewall compaction" (probably more accurately termed "sidewall smearing") can help restrict roots and reduce the number of roots that penetrate out into the bulk soil. Once we have planted, about all we can do is watch for this problem and hope for rain to soften the soil. There isn't an effective "cure," though row cultivation can help aerate soils. Cultivation will, however, break some roots unless it's done when plants are very small.

Corn planted here on April 23 has three or four leaf collars visible now. Bob Nielsen has data showing that it takes about 125 growing degree-days (GDDs) for plants to emerge, about 85 GDDs per leaf stage up to the 10-collar stage (typically about waist to chest high), and then 50 GDDs for each additional leaf stage up to tasseling. We have accumulated about 350 GDDs since April 23, and the crop emerged in about 120 GDDs. So there have been about 230 GDDs since emergence, which would predict that the crop would have about three leaf collars. That's close enough, but you should expect GDD-based predictions to often miss by a leaf stage or two, depending on temperature fluctuations in soil and air and other factors that we don't always understand very well.

Except for the serious wind-related injury that emerged fields experienced on May 3 and 4 and some water-related injury, though, the crop is developing fairly well in most fields. The pale color of leaves in many fields is related to cool, cloudy, wet conditions and should improve quickly with sunshine and warmer temperatures, though night temperatures in the upper 30s and lower 40s will slow the return to normal green color. Remember that leaf area of the first leaves to emerge is quite small, and as long as they can be replaced by newer, larger leaves, the growth of the plant should continue without much interruption.

One recurring question that I get in small numbers each year is what to do about planter errors (we'll blame the planter here, not the operator!) that result in very high populations. One of the interesting questions this week was about a planter unit, one of 16 on the planter, that somehow dropped about five times the normal population in one row over about 30 acres. One concern in this case was on the possible effect of this row on adjoining rows. I doubt that would be a problem, because plants that are only an inch or so apart in a row will compete so much with each other that they probably won't compete much more than usual against adjoining rows. They will use water faster, though, and this could be a problem if water is limited, at least through pollination. We would not expect such a row to produce high grain yields, though, because of the excessive population.

I suggested that it might be a good place to creatively use a (probably retired) weed buggy and wipe plants with Roundup on some sort of repeating pattern to kill 80% of them or so, as long as that can be done without leaving long gaps; ideally, there ought to be two undamaged plants per foot of row and no partially damaged ones that will still compete. Doing this with a hoe or some other mechanical device would be more certain, probably, but would tend to damage roots of standing plants. Our past studies have shown that plants like this probably can be thinned up to knee high or so and still yield like a normal population. In this particular case, there was less than two acres of corn at the high population, so that might limit the amount of time and expense that can be spent trying to fix the problem.--Emerson Nafziger

Author: Emerson Nafziger

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