Learning more about copper resistance and implications on-orchard

12 July 2018

KVH and Zespri, along with science partners, have been focussed on learning more about copper resistance over the years and we have made great progress in our understanding of this complex subject area. A science workshop was held early July to discuss latest research results and further requirements, with the aim of answering the question: “How does our knowledge from the laboratory translate to the field?”

Participants in the workshop came from Otago University, Massey University, Plant and Food Research, Hills Laboratories, and Verified Lab services as well as KVH and Zespri.

Russel Poulter from Otago University presented DNA sequencing results from more than 100 Psa samples that were collected from across North Island growing regions. The main learnings from this work show that there are low level resistant Psa bacteria with some resistance to copper present in all North Island regions. The mechanisms leading to resistance are present in other bacteria and are transferring to Psa. To date, approximately eight different resistance mechanisms have been identified with the most common ones present in all regions. Some of the mechanisms are very efficient at transferring from other bacteria in the environment to Psa (leading to an increased presence of these strains) while other forms are less efficient and less prevalent.

Joel Vanneste from Plant and Food presented the results of an intensive study carried out on a Te Puke orchard where young kiwifruit plants were placed in 10 different locations in the canopy at different times throughout the year and Psa bacteria on each plant was analysed. The learnings showed there is huge variability in forms of low level resistance present on-orchard and between locations, even within the same orchard. Both low-level resistant and non-resistant strains can be readily present at a location - even on the one leaf. Multiple resistance mechanisms can also be present at the one location.

Copper spraying at recommended rates is still effective at killing Psa strains with resistance mechanisms. Timing of spray application and weather conditions can have a big impact on the efficacy of copper use. Further analysis of the samples collected is planned to provide more information, which along with additional research will help us in reviewing our recommendations around copper spraying.

Advice for growers on how to reduce the potential for copper resistant bacteria to impact copper spray efficacy is:

· ensure full label rates are used and good canopy coverage is obtained (the use of spreaders will assist improved coverage),

· look to alternate copper use with other protectant sprays when timing permits,

- extending the timing between copper sprays when risks of Psa are lower (hot, drier weather) may help reduce resistant populations as a percentage of total Psa populations.