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Staging corn development in 2019

Staging corn development in 2019
By Abendroth, L.J., R.W. Elmore.et.al.
 
Corn development varies tremendously across Ohio because of planting dates that range from late April to early July. Some corn is tasseling and silking but in many counties, corn stages range from V7-V12. Moreover, it is not unusual to see striking differences in plant height and growth within cornfields.
 
It is important to understand corn growth and development in order to determine the health and status of the crop for effective use of management practices (e.g. application of post-emergence chemicals) and assessment of stress events (e.g. flooding, drought, hail, etc.).
 
Staging corn development is usually fairly straightforward. Starting with the first leaf, which has a short rounded leaf tip (sometime characterized as the “indicator” leaf), count the number of leaves with visible leaf collars. The collar is the yellow green band that appears at the junction of the leaf blade and leaf sheath.  Counting leaf collars to determine the vegetative stage is feasible until the lower leaves can no longer be identified. At about the V6 (six-leaf collar) stage, increasing stalk and nodal growth combine to tear the smallest lower leaves from the plant. This results in degeneration and eventual loss of lower leaves which makes it difficult to locate the lower leaves (especially the first rounded leaf). Weathering as a result of excessive rainfall, leaf senescence, and chemical applications also contribute to lower leaf deterioration.
 
You can estimate what leaf stage of development a particular field is at using its planting date and the growing degree days it is accumulated since planting. University research indicates that from VE to V10 (ten leaf collars), leaf emergence occurs for every 82 to 84 GDDs accumulated (Nielsen, 2008; Abendroth et al., 2011). From leaf stage V10 to the final leaf, leaf collar emergence occurs more rapidly at approximately one leaf every 50 GDDs.
 
The following examples (from Nielsen, 2019) show how to apply this information
 
 “A field was planted on April 28, but you do not know exactly when it emerged. Since planting, approximately 785 GDDs have accumulated. If you assume that the crop emerged in about 120 GDDs, then the estimated leaf stage for the crop would be about V8. This estimate is calculated by first subtracting 120 from 785 to account for the estimated thermal time to emergence, then dividing the result (665) by 82 (equal to V8.1).”
 
“A field was planted on April 28 and emerged on May 5. Since May 5, approximately 1220 GDDs have accumulated.  Your familiarity with these calculations tells you that the crop is likely beyond V10 (equal to 10 x 82 or 820 GDDs since emergence). So, first subtract 820 from 1220 (knowing the crop is at least at V10). Divide the result (400) by 50 to equal 8 additional leaves; for a total estimated leaf stage of V18.”
 
Growth-limiting stresses and conditions (soil moisture deficits, nutrient deficiencies, compaction, etc.) affect the accuracy of these predictions (Nielsen, 2019). Nevertheless, this method may be useful in timing when plants reach an approximate stage of growth.
 
Another method for the staging development of older plants (with few or no lower leaves) requires first splitting the stalk neatly down the middle and looking for the first noticeably elongated stalk internode. This internode is usually ½ to ¾ inch long. Carefully identify the leaf whose leaf sheath attaches to this node. The fifth leaf is usually attached to the node above this elongated internode. Continue counting the remainder of the leaves with leaf collars to complete leaf stage determination of the plant.