PSA S PATH THROUGH HAYWARD IN ITALY

Transcription

1 PSA S PATH THROUGH HAYWARD IN ITALY Kiwifruit Journal Psa Scientific Edition July/August 2012 CALLUM KAY AND MARIAROSARIA MAZZEO - ZESPRI ITALY The New Zealand kiwifruit industry is closely watching the evolution of Psa in Italy. Here, ZESPRI s Callum Kay and Mariarosaria Mazzeo report on the impact of the Psa disease on Hayward orchards in Italy. There is considerable interest around the fate of the Hayward cultivar in Italy following Psa infection. This article summarises many of the observations and data collected by ZESPRI in the last couple of years to ascertain the real impact of Psa on Hayward. Besides China, Italy is the world s largest kiwifruit growing country. It is a free market and kiwifruit is grown, packed, bought, sold, and traded by many competitive parties. It is packed to varying grade standards and in a wider variety of sizes (sometimes down to as little as 50grams) than would be economical in New Zealand. There are a large number of different varieties available to growers, under a number of different patents and models in relation to PVRs. Some plants are simply sold at the nursery at an elevated price with no further support, marketing or sales return given or expected. In any given year, Hayward returns in particular are influenced primarily by the total volume of the crop at a national level. When the crop is very high, prices are typically suppressed (orchard gate returns (OGR) of 0.20Euro per Kg). Sometimes returns fall below the cost of production for some growers, while in years where the overall crop is lower (primarily due to weather-related events like frost) returns for growers are good (OGR Euro per Kg). Having the large European market on the backdoor step is helpful in controlling shipping and transport costs. Psa in Italy The earliest symptoms of Psa were noticed in 2008 in the Italian province of Latina. It appeared on yellow-fleshed varieties, and secondary symptoms indicated that the disease had likely been present in 2007 but had possibly been noted only as leaf spot. From 2009, more yellow-fleshed orchards noted secondary infection and vine dieback was rapid. This peaked in 2010, in conjunction with a cold and wet spring. Almost all yellow-fleshed orchards in the Latina area had some level of infection. It was at this time Hayward growers in Latina began to notice secondary Psa symptoms. A small number of orchards had seen secondary symptoms in 2009, but it wasn t until 2010 that Hayward really started to be affected by the disease beyond leaf spotting that had been attributed to several bacteria including Pss, Psv and Psa. Figure 1. Map of the Latina growing area - 1 -

2 Like Te Puke, Latina is devoted to kiwifruit. The region grows 40 percent of Italy s.500,000 ton crop. (New Zealand s total kiwifruit harvest is circa 350,000 ton). Unlike Te Puke, it is a flood and swamp plain that visually resembles an area similar to Palmerston North in New Zealand. It is likely that inoculum loads can build up in areas (particularly those prone to cold damage) and then spread into neighbouring areas without any geographical barriers. Contract pruning gangs exist in Latina but typically the contractor industry - in terms of spraying, pruning and even picking - is not as well developed as it is in New Zealand. Rather, groups of growers or extended families move around orchards carrying out necessary work. The area of Latina that has the highest level of infection in Hayward orchards, and the most devastating effects, is the Carano area. This is a small, flat area North West of Cisterna di Latina. Hort16A was also grown in this area and it was these orchards that were removed first. This area is particularly prone to heavy frost with temperatures sometimes sinking to -8 or -9 C in early spring. The severe cold (while not like the colds that can be had in France and Emilia Romagna) can cause cracks and splitting on vines, as well as damage to the softer wood found at the end of canes. This has no doubt contributed to the increased level of infection seen in the area. Infection has spread much further in the Latina area and in 2012 most Hayward orchards (from Aprilia in the north of Latina to Pontinia 40km to the south) have at least some vines that have secondary infection. Many of the younger orchards (5-10 years) have significant levels of infection. Unlike the infection seen on the yellow-fleshed orchards, infection on Hayward appears to be more creeping than devastating. Shoots and smaller canes are affected first (most noticeably exudate is visible at the junctions with larger canes) and for the first season, little progression is seen past this point. Much is made of the hot summer temperatures and limited rainfall in Italy and the growing region s ability to cope better with Psa given the respite from the disease experienced during the dry weather. Unfortunately, it is clearly evident from monitoring data that infected vines remain infected (although progression of the disease is halted in summer). These infected vines continue to be sources of inoculum and collapse once conditions become more favourable for the disease. Images showing the progression of the disease symptoms over three years Image 1. Year one Image 2. Year two Image 3. Year three - 2 -

3 Monitoring over subsequent seasons has seen secondary symptoms move from the canopy to the leader a year later and then this year into the trunk on the most heavily-infected orchards. Early detection of the disease is often hampered by the umbrella growing system used in Italy on Hayward (a multi-leader whorl). While this system provides good protection and canopy cover in the hot summer months (36-40 C), it does make it difficult to see spotting in the canopy due to overlapping canes and older wood present at eye level. Hayward plants that are infected do not readily collapse as has been seen with some yellowfleshed varieties. It is common to see exudate oozing from every cane junction in the canopy but with the vine showing almost no wilt or shoot death for a period of months. It is not until early summer that shoots begin to wilt and die. It is typical to see flowers and small fruitlets shrivelled up on dying cane in mid-summer. The management of Psa on Hayward orchards in Italy The on-orchard management of Psa varies greatly by region in Italy. In part this is driven by the profitability of growers, the suitability of the land for other uses, and the environmental conditions. In Piemonte in Italy s north, growers are typically forced to cut vines back every four to five years due to heavy cold damage (temperatures getting down to -15 C to -20 C). As Psa has become more prevalent in this area, growers have preferred to remove entire orchards and replace kiwifruit with apples and peaches. In Latina, the picture is very different. Horticultural production is centered around kiwifruit, melons, and grapes. Warmer winters and hot summers have made Psa more of a creeping disease. Growers have preferred to remove the season s dead wood at winter pruning time (summer pruning on Hayward is not typically carried out in Latina, although this would be the perfect time to remove infected material). Unfortunately by the time winter pruning happens, many of the exudate symptoms have dried and washed away. The only real indication of a disease problem is the dead canopy wood, which is removed at the junction with living tissue. The removal of wood in this way, with no use of a buffer or monitoring and marking of the vines in the growing season, means the plant generally Image 4. Pruning cuts (red) canker and exudates (yellow and purple) on a Hayward vine in early Spring. remains infected and the disease is left to progress the following season. In short, removing the dead material from the orchard does not remove the infection from the orchard. Crop protection Italian Hayward inputs are typically fairly limited. This in part is due to laws that prevent growers using many of the chemicals that are available in other growing areas of the world, and in part because of the relative cost benefit. The contract sprayer industry in Italy is not as well developed as it is in New Zealand and many growers still have their own spray equipment. Prior to Psa, growers typically sprayed oil to help prevent white peach scale infestation and perhaps a light copper or iprodione to prevent blossom blight and Sclerotinia respectively. Labour costs are relatively high in Italy and growers will take any steps to eliminate labour inputs. Much of the crop is managed by thinning, girdling and the use of hormones rather than by Hi-Cane (which is prohibited in Italy). Post-Psa relatively little has changed. Growers have started to apply 1-2 copper or bordeux in the dormant months after pruning, but beyond that - 3 -

4 there are relatively few growing season applications used to combat Psa. Actiguard is not currently registered for use in Italy on kiwifruit, however several bacillus products like Serenade are registered (or are exempt registration) and are used by some growers. The graphs in Figure 2 show faster softening in fruit from vines with all leaders infected (100 percent infection) over 20 weeks (10 rounds) in cool storage, against those from vines with no symptoms (controls). The same fruit also showed a decrease in peak brix over the same period. Production losses Through the dedicated ZESPRI GREEN packing programme, we can track production changes over time for several heavily-infected maturity areas, looking at yield and fruit size for the same piece of land over several years. It is clear from the table below (Table 1) that there are significant reductions in volume over time of between 3 percent and 20 percent. What makes this story a little more disturbing is that 2011 was a high yield, low fruit size year in general. Typical yields saw an increase of around 10 percent but fruit size fell back 1.5 count sizes. Discussing the impacts of the disease with Hayward growers, and the plan for recovery on orchard, many growers want to work through the disease suggesting that yields can drop as low as 12 ton per hectare (3000 TE) before returns fall below the breakeven point on orchard. Fruit loss and storage On top of actual production losses on the orchard due to Psa, there is also the likely flow-on effect of increased fruit loss due to poorer storability of fruit coming from heavily-infected vines. While storage issues are not as bad on Hayward as those seen with GOLD, storage appears to be compromised and the resulting final eating brix is lower. Fruit that is not managed carefully through the supply chain may further contribute to poorer grower return

5 Pressure over time Figure