Psa and Italian Kiwifruit Orchards, 2011 The Psa-research programme in New Zealand draws on knowledge and experience gained from around the world particularly in Italy, where ZESPRI, Plant & Food Research and several Italian research institutes have been working together on Psa in recent years. On KVH s website, the Newsroom lists several published articles about the situation of Psa in Italy as resource for New Zealand growers http://www.kvh.org.nz/newsroom. From Italy, ZESPRI s Callum Kay has made the following observations, based on first-hand consultation and discussions with ZESPRI s Italian team, about Psa infection of Hayward and Hort16A Kiwifruit vines. While infection data and Psa progression in Hort16A vines has been well documented and communicated (refer to Kiwifruit Journal Jan/Feb and March/April issues) this is not the case with Hayward. Many New Zealand growers want to know what the situation in Italy is with respect to Hayward. Psa and Italian Kiwifruit Orchards an observation by Callum Kay, 4 April 2011 The current situation in Italy The Italian industry is highly fragmented. Orchard management practices differ from orchard to orchard and region to region. The majority of plantings in Italy are Hayward. Many orchards are small hobby farms and, as such, do not have the day-to-day attention to orchards as occurs in New Zealand. Management practices more closely resemble those observed in Korea and Japan with larger, older, multi leader plants. Italian orchards are operated with a low-input system. They carry lots of old wood on umbrella vine structures and produce lower crop loads than achieved in New Zealand. The environmental conditions in Italy are quite different to those in New Zealand. Environmental conditions may influence the rapid development of the disease in late winter and early spring (-8 to +20 C temperatures) followed by the disappearance of many symptoms in mid-summer (+35 C temperatures). Soil conditions are heavy and orchards require irrigation and fertilisation in the summer months. This is usually carried out with little or no understanding of the orchards actual water requirements. Plant stress would typically be higher than would be seen on most orchards in New Zealand. There is no industry-defined plan in Italy for managing orchards infected with Psa. Many growers take no action, resulting in severe infection of their vines, rapid progression to secondary symptoms and rapid spread across the orchard and to neighbouring properties. On many orchards, red and white exudates are seen on vines across the orchard. The vines continue to bear fruit but have lower production volumes with many dead and dying canes in the canopy. The innoculum-rich exudates continue to fuel the problem, releasing Psa into the orchard environment.
Italian Hort16A and Psa In Latina (between Rome and Naples) the situation with Psa infection on Hort16A vines is dire. More than 50 percent of Hort16A plantings (or 350 hectares) have been removed since late 2008 and more hectares are being removed daily. As of March 2011, an estimated 95 to 100 percent of the Hort16A plantings in Latina now have some level of Psa infection. Italian Hayward and Psa During 2010 and early 2011 there has been a rapid progression of the disease on Hayward vines, with secondary symptoms increasingly evident on younger plants. Die-back and white and red exudates have been observed on vines in the Latina, Piemonte, and Viterbo areas of Italy While the extent of Psa infection in Italy on Hayward is not entirely clear, it is estimated around 15% of vines in the Latina region have been removed due to Psa infection. The Italian-based team members consider there is a lot more infection than is talked about or acted upon. The Cisterna and ER local government bodies recently announced a financial support package for kiwifruit growers. This leads us to believe that Psa may be negatively impacting the orchards in those regions. Hayward plants in Italy have multiple leaders (typically four to six compared to two in New Zealand). As such, growers are able to remove infected limbs without production being as significantly impacted as it would be in New Zealand. Initial estimates on the scale of Psa infection and impact on Italian orchards may see productivity for 2011 drop by 25 to 50 percent over the previous year. Rate of infection and spread In Italy (as in Korea), Psa is observed to kill Hayward plants more slowly than Hort16A. We are now seeing more and more Hayward orchards with higher levels of infection and significant exudates and dieback. Dieback has been observed over a period of years and it is common that one affected leader is removed each season. Spring 2011 has seen significant numbers of Hayward vines fail to burst bud on many canes due to Psa infection. It is thought that while the infection is present on the Hayward vines and is not being actively treated or managed, the Psa innoculum is able to spread and establish on the yellow-fleshed varieties. Once Psa establishes itself on the Hort16A vines, it quickly takes hold and is very destructive. The point of initial infection in Italy has still not been confirmed (and is unlikely to be, given relaxed EU quarantine laws). Psa symptoms have taken longer to visibly show in Hayward, but they pose a serious concern to yellow-fleshed and higher returning Hayward growers. These vines may be a reservoir of disease well into the future, effectively eliminating any chance of re-establishing yellow-fleshed varieties in infected regions. Scientific investigations Early investigations in the laboratory observed Hayward plants required a lower level of bacteria to become infected than Hort16A but developed symptoms at a slower rate. It has been observed that younger vines are more susceptible to Psa infection. To support this, one orchard of approximately 20+ years is riddled with infection and oozing everywhere but is still producing crop. Whereas another orchard, which is 5 to 8 years old is almost dead. Page 2 of 8
The spread of disease across Italian orchards demonstrates environmental factors may be implicated, with possible wind plume spread into the Lazio region. The transfer of plant material may be responsible for spread to other regions and into France. Protective spray programmes Hayward growers are not acting quickly or frequently enough to treat or prevent the infection. They apply at most one spray of copper or other protectant spray over autumn/winter. Hort16A growers are now applying three to five sprays of copper or other protectant spray over autumn/winter. The future for kiwifruit in Italy Due to the extent and serious impact of Psa, it is thought that kiwifruit plantings in Italy will be significantly reduced over the next three to five years. Italian Hayward orchard pre-winter pruning Italian Hayward orchard post-winter pruning Typical middle-aged (12) Italian Hayward orchard note; old wood, multiple leaders, and heavy amount of cane. Page 3 of 8
Cane death from Psa infection on old male Hayward Plants; the grower has tried to apply copper but has not removed the infection. Infected cane fails to break bud Page 4 of 8
Leaf spotting Red exudate Page 5 of 8
Very young shoot dieback Very young Hayward orchard (2 years) in late winter showing exudates symptoms. Page 6 of 8
Young Hayward orchard 5 6 years old showing cane dieback, limited budbreak, and exudate symptoms (note the exudate on vines in the background). Orchard as above, multiple sites of symptoms (red circles) note this orchard is still standing little cutting or spraying is happening. Page 7 of 8
Orchard above, multiple sites of symptoms on smaller leaders, with bud break failures. Page 8 of 8