Preliminary results from the latest KVH round of the ongoing Psa resistance and tolerance monitoring programme show a significant increase in the number of samples with a degree of tolerance to copper.

The February/March programme tested 237 samples from 99 KIPNs. Of these, forty-two samples showed low levels of tolerance to copper; and 23 samples showed medium levels of tolerance to copper. These samples were from 56 KPINs. The level of tolerance identified is still below the concentration of copper in a spray tank when applied at recommended rates, but the development is concerning.

The orchards are spread across the growing regions with the majority of orchards identified in Te Puke. The other areas are Whakatane, Opotiki, Poverty Bay, Coromandel, and Kerikeri.

KVH is contacting the owners of the orchards showing medium levels of copper tolerance to review what is happening on orchard and attempt to better understand the potential implications on Psa control. Orchards where copper tolerance has been identified are also required to manage risk items off-orchard to reduce the risk of transferring the bacteria to other locations.

All growers are encouraged to ensure copper is applied at label rates using high enough water rates to ensure complete coverage of the canopy and to follow best practice Psa management advice. This includes a comprehensive spray programme of five copper applications at full winter rates, starting immediately post-harvest and through dormancy. It’s also important to remove infected material from orchards, maintain good hygiene between vines and alternate spray protection products.

In addition to the resistance and tolerance monitoring work being carried out for KVH by Hills Laboratory, Otago University, Massey University and Plant and Food Research are undertaking studies looking at the genome sequence of Psa and how the bacteria is evolving on orchards. All these researchers have identified the presence of additional genes that they believe are associated with copper resistance in Psa. These samples were from a selection of orchards in the Te Puke region. It is important to note these research institutes have each used a different testing methodology to determine the level of copper required to inhibit the bacterial growth and as such, we still don’t know if this development is a significant finding.

KVH will host a collaborative science workshop in May for scientists from Otago University, Massey University, Plant and Food Research and other experts to discuss the findings to date and gain a better understanding of the situation. The objectives include agreeing a standardised testing methodology for resistance/tolerance and steps on how we best manage the increasing risk of Psa evolving and developing a resistance to copper.

Orchards that have been found to have a copper/streptomycin tolerance or resistance should refer to KVH Protocol: Resistance/tolerance to Psa control products.

Any growers concerned they may not be achieving the expected levels of Psa control from copper applications at label rates should contact KVH on 0800 665 825 or email info@kvh.org.nz.