The Impact of Defoliation in High Population Corn Systems at Various Growth Stages.

The increase in plant population in corn results in increasing competition for light within the canopy.  Therefore, it would seem logical that defoliation caused by hail or pests would have a greater impact on yield in high population corn systems. While previous studies have examined the impact of defoliation on corn yield (Vorst, 1993; Adee et al., 2005) these studies were done using plant populations that were much lower than those commonly used by growers today.  This study was conducted to determine whether leaf loss in high population corn systems results in greater yield losses compared to corn grown using lower seeding rates.  Studies were conducted in 2007 and 2009 at two locations in North Carolina using final plant populations over 83 000 plants ha^-1.  Main plots consisted of different levels of defoliation: 0%, 25%, 50%, 75% and 100% of the leaf blade removed. This was achieved by cutting all of the leaves on each plant perpendicular to the direction of the leaf veins.  Subplots consisted of different stages of development ranging from V3 to R5.  Silking dates and plant height for each treatment were recored.  Grain yield was measured using a plot combine.  Regression relationships between relative yield loss measured against the non-defoliated check and the corn defoliation progress curve (CDPS) indicated that the impact of 100% defoliation in high population corn systems is more severe than that reported by Adee et al. (2005).  However, lower levels of defoliation did not have as severe of an impact as previously reported.  The critical period of leaf loss was found to occur at VT resulting in the complete loss of grain yield when 100% of the leaf area was removed.