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Italy: Kiwifruit vine decline heads north-west

Over 300 people took part in the technical meeting on kiwifruit vine decline organised by Fondazione Agrion. The fact that so many took part is a clear sign of how much this issue is worrying producers, technicians, researchers and local institutions. The phenomenon is expanding quickly, it is irreversible and hasn't got a specific cause. 

After learning how to live with PSA (responsible for bacteriosis), here comes a new menace, which so far has already hit 100 hectares in Veneto and 150 in Piedmont.

Ballari Giacomo, President of Agrion, said "we want to help businesses understand plant needs and get some answers. We must cooperate to understand how we can protect the crops." 

Graziano Vittone, an Agrion technician, illustrated the symptoms and how the disease advanced in Piedmont. "Roots disintegrate and there are no root hairs, so the whole tree ceases to function. The phenomenon always starts in specific areas, for example near flow irrigated crops."

Soil condition and composition, the type of irrigation and water requirements are all aspects that must be taken into consideration.

Technician Luca Nari added that "at the moment, it is essential to avoid creating root asphyxia conditions. A study carried out in summer 2016 showed that irrigation in affected kiwi orchards is 2-2.5 times higher than what is actually needed. A correct management of irrigation is therefore essential."

Kiwifruit vine decline: trees start to wilt.

Chiara Morone from the Phytosanitary sector of the Piedmont Region and Laura Bardi from CREA Piemonte illustrated the physiological response of plants to water-environmental stress. Weather anomalies (rainfall and temperatures between May and October) may have affected the physiology of plants, which are very sensitive to temperature changes. For example, the number of days with a temperature change of 18°C between May and September went from the 23 of 2012, to 18 in 2015 and 45 in 2016. 

"Now we must always worry about water monitoring, fertility and soil oxygenation, as kiwis react very badly to weather changes. We have also witnessed a few problems with plums and hazelnuts (sudden leaf loss) which may mean they are affected by a similar disease."

Laura Bardi explained what happens when there is too much water in the soil and the important role carried out by rhizosphere microorganisms and by soil oxygenation.

Root asphyxia - their purple colour is a sign of lack of oxygen. 

Agrion Director Silvio Pellegrino explained that "thanks to the cooperation of the regional phytosanitary institute, we managed to exclude the fact that the disease spreads through insects or pathogens. There is no enemy to fight against, there is only an agronomic problem to tackle."

Kiwifruit vine decline: collapsed orchard.

Lorenzo Tosi from Agrea represented the experience in the Veneto region, where the problem started in the western area near Lake Garda. It all started wth a few hectares in 2012, which became 70-100 in 2013, 500-600 in 2014 and over 1000 in 2016. Technicians observed that the problem did not affect the eastern area, where the soil has a different composition - the territories affected have a 50-60% limestone content against the 20% of the eastern territory. 

"In orchards affected, all plants are destined to collapse, so we are working on the new orchards - high mulching (50 cm min.), organic substance and controlled irrigation with tensiometers."

Photo by Lorenzo Tosi.

Alessio Galoppini, an agronomist from the Verona area, added that "after observing mulched orchards with organic matter (compost), transplants that respect the neck and irrigation only when needed for one year, we could see that plants appeared definitely better than those grown with the traditional technique." 

Photo by Lorenzo Tosi.

"In July, while we irrigated with 6 litres/plant every 3-4 days, producers used between 10 and 20 litres/plant every day, so over-irrigation is definitely a problem that must be addressed. In addition, we also want to study how microbial populations change in soils with affected or heatlhy plants."

Vottone ended the meeting with a few indications. In the orchards located in areas at risk or that present a few collapsed plants, it is important to assess irrigation and root conditions. It is also important to harrow interrow and plough in the middle. A suitable number of branches must be maintained depending on root potential and phytoregulators must be used carefully. Organic matter and suitable soil aeration are essential in asymptomatic orchards.

For what concerns new orchards, first of all, a chemico-physical analysis of the soil is essential. The soil must then be prepared with organic matter, mulching and green manure. The irrigation system must comply with the effective needs of the species, depending on the nature of the soil.

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