Double Pruning of Grapevines: A Cultural Practice to Reduce Infections by Eutypa lata

Abstract

Double pruning of grapevines was evaluated as a cultural management practice for reducing infections by Eutypa lata in spur-pruned vineyards. Double pruning involves two pruning passes through the vineyard. Vines are first prepruned by nonselectively trimming canes to a uniform height, generally 30 to 45 cm above spur positions, then pruned to traditional two-bud spurs in late winter when Eutypa infections are less likely to occur. In large vineyards, double pruning may allow for more final pruning in late winter, potentially reducing the number of infected spurs if Eutypa infections on prepruning wounds do not develop beyond the point where final pruning will occur. To evaluate double pruning, Chardonnay and Merlot grapevines were prepruned monthly from October to February with final pruning in March for three seasons. Eutypa lata spores were inoculated onto wounds at the time of prepruning in two seasons. Examination of inoculated canes after final pruning showed mean lengths of vascular discoloration below prepruning wounds of 0.29 to 4.67 cm in Chardonnay and 0.14 to 3.07 cm in Merlot, with maximum length of discoloration of 14 cm and 12 cm, respectively. Isolations for E. lata were made at various locations along the length of the discolored vascular tissue. Eutypa lata was not recovered from isolations made more than 4 cm below the point of inoculation, indicating that infections of prepruning wounds should all be eliminated during final pruning, as long as prepruning occurs 30 to 45 cm above the final pruning cuts. No impacts on viticultural performance were observed, including yield, pruning weight, and time of budbreak. By allowing for more final pruning to occur in March, double pruning should greatly reduce the number of Eutypa infections that occur each year.