Effect of Defoliation by Simulated Hail Damage on Yield of Potato Cultivars with Different Maturity Performed in Spain

Worldwide, potato (Solanum tuberosum L.) crops cover 18 x 10(6) ha, corresponding to a production of 314 x 10(6) t. The importance of this crop makes it crucial to control production losses and quality defects due to foliar injury, whether by natural or mechanical causes. The artificial defoliation of potatoes is a common technique used to investigate the correlation between damage caused by either hail or insects and yield. The aim of this study was to evaluate simulated hail damage on different cultivar potatoes of varying maturity to quantify the commercial yield reduction attributable to different defoliation levels through the potato crop cycle. Eight trials were carried out in the Central Ebro Valley (northern Spain) over a period of 4 years with three potato cultivars: Jaerla, Red-Pontiac, and Baraka. Four levels of defoliation (no defoliation, slight defoliation, medium defoliation, and high defoliation) were carried out in several phenological stages. The crop yield losses for each level of defoliation were calculated by correlating the percentage of defoliation applied and the resulting percentage of yield loss. Yield reduction equations were calculated for each trial and phenological stage. Damaged produced during tuber formation or flowering considerably reduced yield. In contrast, defoliations after tubers had completed growth barely affected yields. Differences among cultivars with respect to yield losses were noted regardless of location and year. The early cultivar (Jaerla) recovered worse than the longer-cycle varieties (Red Pontiac and Baraka) as concerns defoliation effects. Effects on yield were similar at the different locations. The regression equations presented may be used for modeling the yield reduction due to defoliation treatments caused by different biotic and abiotic agents.