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Issue No. 9, Article 6/May 20, 2005

Smooth Sailing Ahead?

There was some light frost in places on May 16, but in general there has been a welcome return to warmer weather this week, and corn color is improving while the soybean crop starts to emerge. Corn planting is essentially finished in Illinois, and 70% of the soybean crop was planted by May 15. Soybean planting progress will continue in most areas this week, so soybean planting will be timelier than it was in 2004.

Growing degree-day accumulations for May have been close to average in much of Illinois, but low temperatures have alternated with high temperatures to produce corn crop conditions that aren't as good as we would expect after such early planting. Considerable leaf area was lost on the earliest-planted corn, and where that happened the crop is only now reaching leaf area amounts needed to sustain rapid resumption of growth. There were scattered reports of storm damage last week, and in some cases this left leaves twisted and struggling to get out into the sunlight so they could get photosynthesis up and running. While we normally don't get too concerned about the loss of some leaf area in small corn plants, the extent to which such loss delays the onset of rapid growth can become important later in the season. On a GDD basis, it takes 2 or 3 days of delay now to have the crop a day behind by mid-July, but if weather is unfavorable in midsummer, even a day can mean the loss of bushels.

We continue to ponder whether corn yield potential has been reduced by the cold weather and loss of leaf area this year. I haven't found any relevant data to answer this question, so for now we'll concentrate on problems the crop encounters, under the assumption that what happens and how we manage the crop from now on will be more important in determining yields than what has happened up to now.

One concern in some fields is restricted growth of nodal roots on small plants. Symptoms of this are showing up mostly in fields that were planted without tillage or, in some cases, with strip tillage. This problem manifests itself as rolled leaves in the afternoon and purpling in some hybrids, as affected plants undergo mild drought stress, even though there is usually good soil moisture a few inches deep in these fields. The seminal root system reaches its maximum size soon after emergence, and if nodal roots don't begin to grow normally by the 2- or 3-leaf stage, then water loss increases with the increase in leaf area until it exceeds the ability of the root system to take up water. This can thus become a cycle of root restriction and decreasing plant growth rate, and if the lack of nodal root growth persists, it can lead to the so-called rootless corn syndrome. This happens when the nodal roots either fail to develop or, more commonly, grow mostly within the seed furrow--so up and down the row but not out into the bulk soil between the rows. In extreme cases, plants can grow to the 6- to 8-leaf stage before the root system can no longer support growth. Such plants might even break over and die if the problem persists.

We usually see this lack of nodal root development when it remains dry after planting, especially when the planting furrow sidewalls harden as they dry out. It's more commonly seen when planting is done into too-wet soil, but that was rare this year. Some of the corn plants from our April 19 planting into a stale seed bed here at Urbana (tilled in late March but not before planting) are showing such symptoms, even though the sidewalls don't seem restrictive to root penetration. Besides the soil at crown depth being too dry to allow much root growth, the lack of nodal roots also lets the plant move in the wind, further reducing the ability of nodal roots to grow into the soil. Calm weather thus might help, but the lack of surface soil moisture is the real problem, and rain is about the only solution. There have been suggestions in the past to try to cultivate soil into the row to help keep plants standing and perhaps to provide soil for roots to grow into, but most of the affected corn is too small for that, and trying to finesse just the right amount of soil into the row and against small plants is often impractical.

Soybean emergence is somewhat uneven where planted into soils with limited moisture, but we anticipate good emergence in most fields. Planting more than 1-½ to 2 inches deep to get to moisture is not suggested when planting in mid-May, because of the warmer soils and danger of crust formation and poor stands if it does rain after planting. As we've said before, dry weather after planting is usually more favorable for emergence than is wet weather. Emergence of soybean plants generally takes about the same number of GDDs as does corn emergence, though we normally plant soybean into warmer soils during warmer weather so that we have become accustomed to seeing emergence within a week to 10 days. Most soybeans planted in May are emerging within that period of time. While we prefer not to have uneven emergence as a result of uneven soil moisture conditions, we don't have good data to tell us whether or not there is a yield penalty from uneven emergence in soybean. My guess, based on the ability of soybean plants to compensate for reduced growth of nearby plants, is that such a penalty would be minimal when soybeans are planted on time.

Current weather conditions are very good for wheat, and heading is almost complete here in the east-central part of Illinois. There has been some fungicide spraying in some places in Illinois, but there have been no reports of serious or widespread diseases. Fusarium head scab could have infected heads in areas that received rain during heading and flowering. After flowering, every day counts in terms of yield--we normally expect only about 20 days of rapid grain filling in southern Illinois, starting a week or so after heading. That means adding 3 to 4 bushels of yield per day for good yields. Adequate supplies of water and nutrients and keeping the leaf area healthy and intact will be keys to achieving this.--Emerson Nafziger

Author:
Emerson Nafziger

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