Psa is a bacterial disease which affects kiwifruit species. Spread by airborne spores, it can move easily between plants and orchards in certain environmental conditions. The disease has been identified in kiwifruit for at least 25 years but has not been found in New Zealand until a recent identification in the North Island in 2009.
The bacterium was identified on green kiwifruit vines in Italy as far back as 1992 and has had a significant impact on Italian production in recent years. It has since been found in Japan and Korea kiwifruit orchards, where the disease is controlled by implementing appropriate agricultural practices. Good orchard hygiene is the key to reducing spread of any disease
The disease is characterised by brown angular leaf spots sometimes surrounded by a yellowish halo and are seen at the affected sites in New Zealand at this stage. The spots are very easy to identify and no technical expertise is required as can be seen below
At present, Growers are encouraged to check their vines for Psa and those without the symptoms should continue normal activities with increased orchard hygiene whilst carefully considering on site activities in order to minimise any risks.
The key risk of Psa spread is movement of bacteria from infected to uninfected plants and orchards, therefore orchard hygiene is critical. Bacteria spreads through the air, on living or dead plant material, machinery and other equipment. It has been found that the following points are very important in managing the organism:
Our Nuron Organics Product has been tested previously against the known banana moco disease and the results have been very encouraging. Buoyed by this we decided to assess whether our product would be useful against the Psa bacterium since the both the Psa and the moco bacteria are of the rod shaped variety
The methods used to perform the comparison were as follows:
- Zone Inhibition on soft agar plates carried out by Hill Laboratories in Hamilton
- Infected kiwifruit cuttings and leaves from a Te Puke orchard sprayed with Nuron Organics Product and swabbed against non treated sample as control
- Nuron Organics product inhibits Psa‐V in a Zone of Inhibition test undiluted and when diluted 10‐fold. Replicate samples were tested on separate agar plates (only one photo shown as an example). The Inhibition Zone Diameter (in mm) was measured. Nuron Organics product showed Psa‐V bacterial inhibition undiluted and when diluted 10‐fold (please see Hill Report).
- Swabs from Infected cutting and leaf agar plates exhibit abundant growth whilst the treated samples showed nil growth
The first two results (1 & 2) although empirical, showed the Nuron Product to be effective against the Psa. The sumifru results backed this up with 100% kill rate against the moco bacterium.
Whilst further studies may still be required on the ‘field application’ of the Nuron Product on the vines proper, we see a great opportunity for the Nuron Product to be used immediately in the hygiene procedures recommended by Zespri and described above in the introduction.
Thus the Nuron Organics Product could be used for sterilising orchard equipment, hosing vegetative material off machinery before leaving the orchard, hand washing and footwear spray after handling suspect material, whilst further studies could be carried out on the field application of the Nuron Organics Product on the vines proper