Abstract
Results of five trials to determine the effects of different defoliation treatments on onion (Allium cepa L.) crop yield carried out in southern Navarre, in the Central Ebro Valley (Spain) are presented. Yield losses caused by defoliation levels of 0, 33, 66, and 100% inflicted using shears at different plant growth stages were evaluated. The results demonstrated a relationship between yield loss, the defoliation treatment applied, and plant phenological stage. Onset of bulb formation was the most critical growth stage for determining the effect of defoliation on the yield, and yield losses increased with increasing the defoliation treatment. The results were employed to calculate a set of regression equations used in turn to construct curves applicable in evaluating final crop yield losses in onions due to defoliation from such causes as hail storms, wind, insect attack, and other types of mechanical damage.
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