Psa Virus Attacks Kiwifruit Industry

How is the kiwifruit industry coping with PSA disease a season on from its discovery?

We join growers as they battle against the disease in the lead up to harvest.

On Friday 5 November 2010, a bacterial infection was discovered on a New Zealand kiwifruit vine – testing confirmed that the vine infection was PSA on Monday 8 November.

PSA affected orchards have been identified in Franklin, Hawkes Bay, Katikati, Poverty Bay, Tauranga, Edgecumbe, Golden Bay and Motueka.

PSA is an airborne, transmittable bacteria meaning it can be carried via heavy rain, strong winds, on equipment, machinery or plant material, and possibly by insects and bees. PSA presents itself on the vines in a number of forms and experience in other countries suggests that climatic conditions such as a harsh winter followed by a hot summer provides ideal conditions for the PSA bacteria populations to escalate.

Psa pseudomonas syringae pv actinidiae (PSA), has been confirmed on 150 orchards across New Zealand. 114 Psa-affected orchards (76%) are in the Te Puke region. 40 orchards (less than 2% of the industry) have been identified as PSA-V (V is for virulent, formerly Italian-like). All PSA-V orchards are within the Te Puke PSA Priority Zone.

The zone encompasses PSA and non-PSA affected orchards. 14 GOLD orchards in the PSA Priority Zone have been confirmed with secondary symptoms. 45 hectares of PSA-V affected vines have been removed (less than 0.5% of the industry). $10.2 million has been committed to PSA affected growers.

Around 29 hectares of vine have been removed as at mid-February 2011.

John Cook is on the family farm which was converted to kiwifruit in late 1970’s. He has been on the property since that time and has expanded interests in the Te Puke region.

He currently has 4 orchards totalling around 18 canopy hectares. This includes Green and Gold plantings.

John was immediately on high alert following the announcement of first PSA positive orchard. He engaged a team of 4-5 people to walk each orchard and photograph any potential symptoms. He identified some concerning spots on his Te Matai Rd orchard, photos were sent to ZESPRI, samples were taken for testing and have subsequently returned a PSA positive test and a PSA-V isolate result.

When he received the first symptom identification on the orchard, he immediately imposed hygiene protocols on all orchards and effectively quarantined the affected orchard. He’s embarked on an intensive protection and monitoring regime on other orchards – including protective spray applications.

PSA-V has meant that a planned semi-retirement has been put back. John says hands-on management is required. He has faced the reality of having to consider laying off staff when previous plans were to resource-up and grow his orchard interests.

He has cut back the Te Matai Rd orchard to trunk (2.5ha of a 5ha orchard – the remaining 2.5ha are in conversion). He will wait 3-4 weeks to assess the vine and then make a second cut and seal the wound with a latex film (grean-seal)

When the PSA priority zone was established, John saw the need for someone to represent the concerns and interests of the affected growers in the zone and work with KVH on communication and strategy.

He’s worked with a core group of growers to coordinate a meeting to formalise the Action Group and was asked to take the lead role.

He’s currently working to aid communication (to growers in the zone and with KVH), around decision making and advocacy.

John Cook sits on the organisation that is managing the PSA Priority Zone. What they have done is identify the priority zone – which is where the disease is present – and then around that area they’ve placed a High Risk Zone – to act as a buffer to try and prevent PSA from spreading. At the moment those two zones encompass the whole of Te Puke.

He says one focus at the moment is the spray management programme. They are working with KVH to implement this programme – working now and post harvest.

An important aspect of the PSA Management Strategy is to determine with some certainty where the perimeter of more serious infection is, to allow a focused containment effort by growers post-harvest, ZESPRI, MAF and KVH.

Currently there are results for two orchards just outside of the PSA Priority Zone, confirming the PSA-V isolate

On-the-ground orchard monitoring also gives us cause for concern that the footprint for the disease is more widespread than first thought. The situation was not helped by the major storm on the 28th January with strong SE winds which may have pushed the infection NW into the No.1 Road area.

In GOLD orchards with the PSA-V isolate, the disease is advancing to secondary symptoms, leading to some cane die-back and in some cases the release of exudate, which is of particular concern as it is loaded with inoculums.

Hayward Orchards appear less affected, with no orchard showing secondary symptoms. These observations are in alignment with our understanding of PSA progression in Italy in both GOLD and GREEN orchards.

At a recent meeting, it was agreed that the existing PSA Management Strategy should be amended to focus vine removal activities on GOLD orchards with confirmed PSA-V isolate and any orchard with secondary symptoms (GREEN,GOLD or combined).

GREEN orchards that are demonstrating primary symptoms of leaf spotting only, will no longer be required to be cut back to the trunk. These growers will however be required to adhere to enhanced orchard hygiene and spray practices to minimise the spread of PSA from their orchard.

The rationale behind this strategy is that the GOLD orchards are more severely affected by PSA and are carrying higher inoculum loads due to the presence of advanced secondary symptoms. By focussing vine removal activities on these GOLD orchards, they are in a better position to reduce inoculum.

Vines that had been cut out were being carted away.

John Cook says there has been a policy change and those cuttings will now be buried on site in the orchard. It is feared that burning might promote the transferral of the inoculums.

In conjunction with vine removal, Priority Zone folk and KVH recommends a protective spray programme and is continuing to work to identify the perimeter of infection in the Te Puke region.

Wind plume analysis and continued sampling and testing will provide additional information about zone boundaries.

Growers will be compensated for the loss of this season’s crop and assistance packages will cover the costs of removal, sprays and the re-establishment of the canopy through a fund set up by the Government and the industry. The industry is confident orchards would return to full production in the next few years.

Approximately 30 isolate test samples are being collected per week.  The testing process has two steps and the timing of each step is unable to be defined.