Unidentified Issue Triggering Early Fruit Drop in Northern Italy

Since the sec­ond week of August, olive trees in north­ern Italy have been expe­ri­enc­ing pre­ma­ture fruit fall.

The phe­nom­e­non pri­mar­ily affects groves of the Frantoio vari­ety, although some instances of Grignano olives being affected have also been reported.

The groves in ques­tion have lit­tle in com­mon other than their genet­ics. They are located at var­i­ous alti­tudes and in dif­fer­ing envi­ron­ments. Additionally, farm­ing prac­tices vary between the affected groves, includ­ing the pres­ence or absence of irri­ga­tion.

No signs of dam­age from pests or dis­ease have been iden­ti­fied, lead­ing experts to posit that an as-yet-unde­ter­mined com­bi­na­tion of envi­ron­men­tal fac­tors is to blame.

Frantoio is a Tuscan vari­ety cul­ti­vated exclu­sively for its oil, the name itself trans­lat­ing from Italian as ​“olive press.” Known for their resis­tance to dis­eases such as Verticillium wilt and their gen­eral har­di­ness, Frantoio trees pro­duce a per­va­sive root net­work that allows them to sur­vive peri­ods of drought bet­ter than many other vari­etals.

However, Italy expe­ri­enced extreme heat this sum­mer, just like many other Mediterranean coun­tries.

Starting July 15^th, Italy was under an anti­cy­clone that orig­i­nated in the Sahara desert for sev­eral weeks. By the sec­ond week of August, when this phe­nom­e­non was first reported, tem­per­a­tures across the coun­try’s north had reached 40 ºC, push­ing the snow­line to 5,000 meters.

Enzo Gambin, direc­tor of the Inter-regional Association of Olive Producers, told local media that this extreme weather may explain the pre­ma­ture fruit fall in the region.

“When olive trees are exposed to intense sun­light for a pro­longed period, the tem­per­a­ture of leaves and fruit can increase sig­nif­i­cantly, trig­ger­ing a state of heat stress,” he said.

“This phe­nom­e­non occurs because high solar radi­a­tion causes an increase in inter­nal plant tem­per­a­ture, which in turn stim­u­lates increased tran­spi­ra­tion, a process by which plants lose water from leaf stom­ata,” Gambin added.

Transpiration is a nat­ural and vital process that serves many pur­poses, one of which is cool­ing. This is achieved in the same way that per­spi­ra­tion cools ani­mals, reduc­ing inter­nal tem­per­a­ture through sur­face evap­o­ra­tion.

An imbal­ance occurs when the amount of water lost through tran­spi­ra­tion is greater than the amount of water avail­able or when it occurs faster than the plan­t’s abil­ity to absorb avail­able water.

Because water is crit­i­cal for the cor­rect func­tion of every­thing from nutri­ent trans­porta­tion to cell integrity, an imbal­ance can severely and rapidly impact a plant’s health. Various mech­a­nisms can be trig­gered to mit­i­gate this impact.

The first is the clo­sure of leaf stom­ata to reduce fur­ther water loss through tran­spi­ra­tion. However, this has the addi­tional con­se­quence of reduc­ing pho­to­syn­the­sis, which reduces the amount of energy avail­able to the plant.

When these cir­cum­stances per­sist for an extended period, more extreme mech­a­nisms come into play, includ­ing the sac­ri­fice of fruit, leaves, and even branches, to increase the chances of the plan­t’s sur­vival.

Gambin believes that this may be what is occur­ring, although he added that patho­log­i­cal causes can­not be ruled out at this stage.

“Further stud­ies and mon­i­tor­ing will be nec­es­sary to fully under­stand the spe­cific causes of this phe­nom­e­non and to develop effec­tive man­age­ment strate­gies that can help olive grow­ers mit­i­gate the impact of fruit drop,” he said.

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