NZ: Kiwifruit vine disease Psa shows resistance to key treatment
Results from the Kiwifruit Vine Health (KVH) regular testing program have shown Psa-V resistance to streptomycin in two Te Puke orchards.
The detections were made in the most recent tests of an ongoing copper and streptomycin resistance monitoring program, which has been in place since 2011 and aims to ensure resistance is detected early.
KVH said in a release these finds were 'not completely unexpected'.
It added the streptomycin-resistant Psa-V was still susceptible to copper, meaning growers could still 'effectively control' Psa-V.
"Resistance to streptomycin can occur naturally, even on orchards where streptomycin has not been used," the group said.
KVH and single-desk marketer Zespri are working with the relevant authorities to understand the implications of this result. Other orchards in New Zealand could also have streptomycin resistance.
The plant health body also stated there was no evidence to suggest the resistance had occurred due to inappropriate use of streptomycin.
Streptomycin use and resistance has previously been identified in other horticultural industries in the island country, and successful management strategies have reportedly been developed to deal with this.
The release went on to say that industry use of streptomycin, registered and sold in NZ as KeyStrepto, was not permitted at this time of year under Zespri’s Crop Protection Standard.
"KVH and Zespri are reviewing the kiwifruit industry use conditions of Streptomycin for the 2016 season and will notify the industry once this is confirmed in June," the group said.
"Through the R&D and product testing programme Zespri and KVH are continuing to test and identify alternative and sustainable control approaches for Psa-V. Zespri has been developing options to reduce industry reliance on antibacterial products.
"Both orchards have been working with KVH to ensure best practice resistance management is in place. This includes the application of copper spray, movement restrictions on plant material and a strong focus on orchard hygiene."
Intensive sampling and testing of the two orchards and the surrounding orchards is underway. Further testing is also being carried out to establish the nature of resistance.
In terms of advise for growers, KVH urged orchard management plans to be adhered to, as well as a robust protective spray program, orchard hygiene and the removal of infection from orchards.
The group added it was very important to use protective spray products at label rates.
Streptomycin is an antibacterial product and has been registered for use against Psa-V in New Zealand since 2011.
Antibacterial products are registered for use in Canada, United States, New Zealand and a number of Asian countries against a range of bacterial diseases in horticulture, including fire blight in apples and pears.
It is registered in New Zealand for use on apples, tomatoes, stonefruit and kiwifruit.