Results from KVH’s regular testing programme have showed Psa-V resistance from samples in two Te Puke orchards.
These finds were detected in the most recent round of an ongoing copper and streptomycin resistance monitoring programme that has been in place since 2011. The programme’s aim is to ensure resistance is detected early. These results are not completely unexpected.
The streptomycin resistant Psa-V is still susceptible to copper, meaning growers can still effectively control Psa-V.
Resistance to streptomycin can occur naturally, even on orchards where streptomycin has not been used. KVH and Zespri are working with relevant authorities to understand the implications of this result and other orchards in New Zealand could also have streptomycin resistance. There is no evidence to suggest the resistance has occurred due to inappropriate use of streptomycin.
Streptomycin use and resistance has previously been identified in other horticultural industries in NZ and successful management strategies have been developed to deal with this.
Streptomycin use not permitted at present
Industry use of streptomycin (registered and sold in NZ as KeyStrepto™) is 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.
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.
What is being done?
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.
What can growers do?
KVH continues to recommend growers adhere to their orchard management plans, including a robust protective spray programme, orchard hygiene and the removal of infection from orchards as per KVH’s best practice advice through autumn. It is also very important to use protective spray products at label rates.
Refer to the KVH Seasonal Management Guide at www.kvh.org.nz/seasonal_advice.
Kiwifruit growers who believe spraying is providing no control, and suspect resistance, should contact KVH on 0800 665 825 or email email@example.com. KVH will then assess the situation and carry out additional testing for resistance as required.
What is streptomycin?
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.
Why is it used in the NZ kiwifruit industry?
MPI granted a Limited Label Claim with strict use conditions for streptomycin for the control of Psa-V on kiwifruit vines.
Antibacterials are considered to be one of the most effective tools for managing Psa-V infection. For information on efficacy refer to: www.kvh.org.nz/product_testing_results.
How has resistance developed?
We are still investigating the exact nature of the resistance but this can occur naturally as a result of other bacteria “sharing” their DNA.
Bacteria can also sometimes change genetically to resist protective products, meaning they are no longer effective against Psa-V. For more information refer to Plant & Food Research scientist Joel Vaneste’s technical presentation on KeyStrepto™ use and resistance on YouTube (link here).
Overseas experience has seen resistance develop in Pseudomonas sp. against both copper and antibacterials. Ceasing use of the product for a period of time is the key way of overcoming resistance.
Why did the NZ kiwifruit industry introduce streptomycin to the CPS if resistance has developed with its use in other industries?
When Psa-V was discovered in NZ, antibacterials were considered a necessary tool to help control Psa-V and allow commercial production to continue. Advice was provided to growers to limit the development of resistance through alternating protectant products, using recommended label rates, ensuring good spray coverage and maintaining orchard hygiene and removing infected material from orchards.
Will KeyStrepto™ be removed from the Zespri CPS?
KVH and Zespri are reviewing the ongoing kiwifruit industry use conditions of KeyStrepto™ in the Zespri Crop Protection Standard and industry will be advised once confirmed. We expect this decision to be made in June.
Is there another antibacterial growers could use instead?
Zespri is also reviewing the data on another antibacterial product Kasumin (active ingredient kasugamycin) to determine if it will be included in the 2016 Crop Protection Standard. This decision will be communicated to industry in June as well.
Can growers still use streptomycin?
Industry use of streptomycin is currently prohibited under Zespri’s Crop Protection Standard until its use conditions have been confirmed.
Zespri does not allow applications of KeyStrepto to fruit and has a zero-antibiotic residue policy underpinned by a 100 percent residue-testing programme of all orchards for antibacterial residues. All orchards are also subject to a multi-residue test, which tests for 300 active compounds. In the four years this testing programme has been in place, no antibacterial residues have been detected in crops.
What commitment is there to finding sustainable ways to manage Psa-V?
To date, more than $12m has been spent on a global research and development programme for Psa-V since it was detected in 2010; and a further $2m per year is committed to R&D into the future.
The R&D programme includes a product testing programme developed to identify, rigorously test and get permission to use suitable products to help manage and control the spread of Psa-V. To date, more than 300 products have been tested for efficacy against Psa-V in the KVH/Zespri product testing programme.