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Nosing back of corn ears caused by a number of things
By Clyde Burchett
Pioneer Hi-Bred agronomist
What are some possible causes of the nosing back of corn ears?
--Less than perfect conditions at pollination may cause the silks at the tip of the ear to emerge after most of the pollen has fallen. Therefore, the tips may not have been pollinated. The cob will remain its normal color.
--Imperfect growing conditions after pollination may cause kernel abortion at the tip of the ear. This is evident by the drying up of kernels. They will be yellow in color.
--Insect feeding on the silks. The feeding of grasshoppers and corn rootworm adults on emerging corn silks may have interfered with pollination in some fields. Sometimes, these ears will also have a scatter-grain appearance.
--Nutrient deficiencies also may cause kernel abortion at the ear tip.
--High plant populations relative to growing conditions. You may see some kernel tip abortion to adjust to growing conditions. This is thought by many agronomists to be a sign that you had a high enough population. If you didn't have some tipping back you may want to consider higher populations in future years.
Monitoring the development of the milkline in corn is a good way to estimate the number of days left until maturity. The milkline is the line separating the starchy area from the milky endosperm. The milkline will move down from the crown of the kernel to where it attaches to the cob at about one-quarter of an inch of the length of the kernel per week. An ear with most kernels at half milkline will be about two weeks from black layer. The chart below can be used to compare the kernel developmental stage to days left until maturity, grain moisture and plant moisture.
Stage, Days until maturity, Grain Moisture %, Plant Moisture %
--Dough, 30-35 days, 70%, 80%;
--Early Dent, 20-25 days, 50%-55%; 70%-75;
--Milkline, 10%-15%, 35%-40%, 65%-70%;
--Black Layer, 0, 30%-35%, 55%-65%.
At physiological maturity, a dark layer (black layer) develops at the tip of the kernel. This layer can be observed by splitting the kernel lengthwise with a knife. The presence of the black layer indicates that the kernel has reached maximum dry weight and is no longer receiving photosynthate from the plant. Black layer generally occurs at grain moisture of 30 to 35 percent.
Rust on corn--is it a problem? It may be, especially if it is southern rust. Both common rust and southern rust can be found on corn plants this time of year, but southern rust causes much more damage. The two rusts look fairly similar, but southern rust will be a lighter, orangish color than common rust, which is usually a darker brick red. Southern rust pustules are more numerous, smaller and smoother edged and are found on the upper side of the leaves. Common pustules are larger with a jagged appearance occurring on both sides of the leaves and sheaths. A combination of early planting and harvest is the best defense against southern rust since there are few hybrids with high levels of tolerance.
Editor's note: Crop Talk is brought to you by agronomists serving your community to keep you informed about current growing conditions and important management issues. Clyde Burchett, Higginsville, Mo., is an agronomist with Pioneer Hi-Bred.
Date: 8/26/04
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