It’s possible for Psa-V to change genetically in order to develop resistance to chemicals or compounds that are currently used by growers to manage the disease. In other words, they would no longer be effective against Psa-V.

As few products are currently known to have efficacy against Psa-V, the loss of one or more of these due to resistance would make Psa-V much more difficult to manage. This would be a significant issue for the kiwifruit industry.

To date, Psa-V resistance has not been identified in New Zealand kiwifruit. However, overseas experience has seen bacterial resistance develop against copper and antibiotics. It can happen as a result of products not being used properly, or being over-used.

Ongoing testing as part of the KVH/Zespri R&D programme is underway to identify early any strains of Psa-V showing potential resistance.

It’s essential the kiwifruit industry is aware of this potential issue, and carries out best-practice management to avoid resistance.

Preventing Psa-V developing compound resistance
Growers and the industry can help reduce the risk of Psa-V developing compound resistance by following these simple steps.

• Always read and follow label instructions, including the recommended label rates. Using products at lower rates can cause resistance to develop.
• Use a combination and/or alternate effective products. This avoids applying the same compound/chemical multiple times in a row—making resistance more difficult to develop.
• Reduce diseased material in the orchard by ongoing management and removal of infected material.
• Maintain best-practice orchard hygiene.

A coordinated approach incorporating the above strategies across the entire industry will reduce the risk of resistance developing.

Kiwifruit growers who believe spraying is providing no control, or suspect compound resistance on their orchard, should contact KVH on 0800 665 825 or email info@kvh.org.nz.

KVH will then assess the situation and carry out additional testing for resistance as required.