Psa Update 2013

September 2013
An overview of the Psa problem in the kiwifruit industry, the $20 million dollar research programme around it and how two growers are responding to the presence of this debilitating disease in their orchards.

Orchardist Robbie Ellison says it has been a "topsy turvey" time since Psa broke out only 200 metres away from one of his orchard blocks at Te Puke. Pseudomonas syringae pv. actinidiae (or Psa-V) is a pathogen causing a bacterial disease on kiwifruit vines around the world. It causes plant dieback and subsequent production loss, or complete destruction of infected plants. It was identified at an orchard in Te Puke in November 2010. Nearly three years on, over 2,000 New Zealand orchards have been infected by Psa-V, which is about 70% of all kiwifruit orchards in the country.

Robbie has 20ha kiwifruit in four orchards, all within 1km of the original Psa epicentre at Te Puke. A grower for 30 years, he has lost about a third of the productive orchard area as a result of Psa, including all his Hort16A gold kiwifruit vines. With much of his productive area decimated, Robbie says he's "done a lot of fishing" since Psa broke out.

When Psa first became public knowledge, the affected orchards were only 200m from the front gate of the Ellison orchard. Just four days later they found Psa in one of their blocks, but managed to grow the crop through to harvest in 2011. That block was cut out in September 2011.

One young block which hadn't yet cropped was cut out in February 2011. It had come under pressure from Psa very quickly. These areas were grafted to the Gold3 variety, which will crop in 2014. Robbie says they were extremely lucky that the green Hayward crop in the same orchard, which came close to being cut out, has produced its best crop this year. In winter 2011, they removed a gold crop on the same orchard, grafting it over to G3, and now it has a full canopy.

One major change in the way they run their orchards is they have to do a lot more spraying. Previously five or six sprays would be aplied each year, but now 11-12 sprays are required to control Psa. There are two critical periods when the vines are more susceptible; in autumn and spring. At leaf drop there are more entry points for the disease, and the weather can be changeable. In spring, more wind is prevalent (being a vector of the disease) and vines are softer (making them more susceptible to damage and subsequent infection). These are the times of year when the Ellisons need to be even more proactive.

Robbie says Psa has created some opportunities - his three sons have developed a grafting business in response to an increased need in the area. They grafted 60ha last year and are doing a similar area this year.

Despite his continued survival in the sector, Robbie is aware of many others who have lost their shirts to Psa. He says, "We have been less affected than many others."

One other positive outcome fo the arrival of Psa is that it has hastened new varietal development and management techniques. Graham Cathie has eight orchards, one of which is gold, the rest are planted in the green Hayward variety. He also manages other orchards.

In a large scale commercial trial, Graham has just finished building a plastic cover over 0.9ha of Gold3 vines (which have been converted from Hort16A). Made in Korea, the plastic sheet is a three-layer laminate which has a UV retardant on the outside and the inner layer has a moisture retarding agent which will hopefully reduce condensation. There is another 7ha of Gold3 vines which remain uncovered, and which are acting as the control for the trial.

Graham built the $100,000 cover because there is some evidence suggesting Psa is spread via water. Without moisture on leaves, the bacteria lose the ability to be transmitted. "We are not saying this is the answer, but we are excited about it. We think it is a good option", Graham says. He's also hoping the cover will offer other benefits for increasing daytime temperatures, and lead to better quality fruit production.

Potentially the crop is very valuable, which justifies the cost of the canopy, which Graham paid for himself. "We did suggest Zespri help pay but they politely declined. However they are helping with a research project. The big issue is learning how to grow kiwifruit in a greenhouse. It's a whole new learning experience." Zespri has put a weather station inside the cover, and one outside to compare conditions.

It is becoming increasingly clear that it will not be one solution to the problem of Psa. Successful growing in the presence of the pathogen will need good orchard management, good cultivars, and an understanding of the bacteria and how it interacts with the kiwifruit vine.

Dave Tanner, General Manager of Science and Innovation with Zespri talks about a $20million research programme, shared between Zespri and Plant & Food Research, which is studying four main aspects:

  1. Understanding the bacteria.

  2. Breeding for long term tolerance and resistance.

  3. Understanding the plant interaction with the environment - what impact the weather has on the plant's tolerance and the growth and activity of the bacteria.

  4. Management tools and techniques such as agrichemical use, plant husbandry and plant nutrition.

They are employing a whole-industry approach to counter the disease, and have also had support, predominantly (but not exclusively) through sponsorship of the research and development programme from ANZ and Rabobank.

One very successful aspect of the research and development has been using translators to get information out from the scientists to the growers.

Dave says the barometer of grower confidence has gone from low to moderate to high. "While the disease is now in most growing locations, most of the regions are in recovery mode. The Psa epicenter in Te Puke is now coming right", he says.

"I don't want to play it down, but in the long term I don't think it will be the devastation we thought it could be. There are growers who have lost their livelihoods but increasingly we have more tools and more knowledge to avoid that outcome."