Breaking the Psa disease cycle
Autumn is an important time for all growers, and especially those with developing kiwifruit blocks, or sites that suffered high levels of Psa infection last spring. Now is the period to monitor for Psa infections in trunks, leaders and canes and develop a strategy for removal of these either ahead of or as part of winter pruning rounds.
Research into the timing and cause of spring bud rot infection has clearly shown that the appearance of bud rot, its rate of increase and final severity can vary greatly across blocks with the same microclimate. This indicates that orchard factors play a large part in the Psa disease cycle. Studies showed the level of overwintering cane infection is a key driver of the higher bud rot levels. We know presence of Psa cankers increases the risk of disease spread to highly susceptible late grown tissue through autumn and again in spring. Inoculum produced from infected vines drives both leaf spotting and bud rot.
Autumn or winter cut out rounds offer an opportunity to break the disease cycle and minimise future impacts going forward.
Removal of infected material from the orchard is highly recommended as Psa can survive for months within infected tissue. Good tool hygiene practices are needed to avoid the risk of transferring infection between vines and application of pruning paints further reduces infection risk.
A spray programme incorporating copper and Actigard following harvest and throughout the leaf fall period is also a critical component of a Psa management strategy.
Image: Cankered Gold3 leader