Simulation of the effect of hail damage on vineyards in Jajarm city, North Khorasan

Every year, a large amount of horticultural and agricultural products are destroyed due to the destructive phenomenon of hail. In this study, the effect of hail damage on quantitative and qualitative traits of three commercial grape cultivars in four different levels of aerial part destruction as a factorial experiment based on randomized complete blocks in two replications during two years (2016 and 2017) in one of the vineyards of Garmek village,Jajarm city of North Khorasan province has been studied on 8-year-old grape plants with similar management conditions. For this purpose, grape cultivars were as the main plot treatments and simulated hail stress at five levels,including control (without stress), 25, 50, 75 and 100% defoliation were as sub plot treatments. Plant yield,bunch number, length and width of bunch, weight of bunches and berries,pH ,percentage of sugar and the taste index of the treated and control plants were determined.The results showed that defoliation due to hail reduced the yield of plants as compared to control plants and minimum yield was observed in 100percentdefoliationtreatment. Decreasing plant yield was mainly due to the decrease in the number of bunches per plant and the weight of a single bunch was not significantly affected by defoliation except in 100% treatment.The results showed that there was no significant difference between the size and weight of berries in the control treatment with 25, 50 and 75% hail defoliation and it seems that thinning and reduction in yield and number of bunches has maintained the size of berries in plants affected by defoliation. The results revealed that the increase in fruit quality due to decrease in the amount of defoliation treatment with intensity of 25 and 50% has caused a slight increase in sugar content, pH and consequently fruit flavor index due to reduced yield per plant.