By Peter Thomison, Field Crop Production Specialist

When estimating yield losses in corn due to hail, frost and other types of plant injury, it’s essential to establish the stage of plant growth at the time damage occurred. It’s also important to know corn stage of development in order to apply post-emergence chemicals effectively with minimum crop damage. 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). When identification of specific leaf collars on plants is not possible, how can the leaf stage of development of a field be estimated?

Given an understanding of corn leaf stage development and heat unit (growing degree days,  (GDD)) calculation, a grower can estimate what leaf stage of development a particular field is at given its planting date and temperatures since planting.

Corn leaf developmental rates may be characterized by two phases. Purdue University research indicates that from VE to V10 (ten leaf collars), leaf emergence occurs approximately every 82 GDDs accumulated. From V10 to tasseling (VT), leaf collar emergence occurs more quickly at approximately one leaf every 50 GDDs accumulated. Iowa State University findings relating leaf appearance to GDD accumulation are similar — from VE to V10, a new collared leaf appears every 84 GDDs accumulated, and from V11 to VT, each leaf appears at approximately every 56 GDD accumulated.

Example (from Purdue University, R.L. Nielsen, 2014): “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).”

Growth-limiting stresses and conditions (soil moisture deficits, nutrient deficiencies, compaction, etc.) affect the accuracy of these predictions. Nevertheless, this method may be useful in timing when plants will reach an approximate stage of growth.