How Cold Temperatures Can Help Olive Production

Over the past month, olive oil pro­duc­tion areas such as Italy, Greece and Croatia were affected by excep­tion­ally low tem­per­a­tures and snow at low alti­tudes. Apulian olive groves at sea level have been whitened by snow­drifts for days.

Italy reg­is­tered unusu­ally severe win­ters in 1929, 1956 and 1985 that caused dam­age to the olive sec­tor and agri­cul­ture gen­er­ally. The cold can affect the wood of olive tree if the min­i­mum tem­per­a­ture drops below ‑7°C (19.4°F) for 8 – 10 days, and cause irrepara­ble harm to the canopy and trunk if they fall below ‑10/-12°C (14/10.4°F) in a few hours.

In broad terms, it is prefer­able to choose native vari­eties for their abil­ity to adapt to soil and weather con­di­tions in their region of ori­gin, and a few days under the snow can have pos­i­tive effects on the devel­op­ment of an olive tree and its pro­duc­tion. It is not with­out rea­son that an old rural Italian proverb says in rhyme, Sotto la piog­gia, fame; sotto la neve, pane, which means ​“Under water, famine; under snow, bread.”

“This win­ter was gen­er­ally very cold with wide­spread frosts and snow­falls in large areas of the coun­try,” said Nicolangelo Marsicani, an expe­ri­enced olive grower from Campania which man­ages 6,000 olive trees in Sicilì di Morigerati, located in the National Park of Cilento, Vallo di Diano and Alburni.

“The cold is crit­i­cal to allow a period of veg­e­ta­tive rest and pos­i­tively impact the devel­op­ment of the olive tree. Alongside fewer day­light hours and less time for pho­to­syn­the­sis, the period of dor­mancy due to low tem­per­a­tures pro­motes flow­er­ing.” In fact, last win­ter in Italy tem­per­a­tures did not decrease enough in sev­eral areas, and this was blamed for a drop in pro­duc­tion.

“An undoubted advan­tage of low tem­per­a­tures and snow is the reduc­tion of the olive fruit fly pop­u­la­tion,” Marsicani observed. In late fall and win­ter, most of the last gen­er­a­tion’s lar­vae leave the olive and pupate in the soil; their vital­ity is under­mined at around 0°C (32°F) and a high mor­tal­ity rate can be reg­is­tered if tem­per­a­tures drop below ‑5/-6°C (23/21,2°F) for some days, espe­cially for those lying in the top lay­ers.

A fur­ther ben­e­fit given by cold weather is the con­tain­ment of fungi. ​“Diseases such as Peacock spot, which is caused by the Spilocaea oleaginea, are often over­looked,” our farmer con­sid­ered. ​“However, when dam­aged leaves fall, the decreased pho­to­syn­thetic sur­face will affect devel­op­ment and pro­duc­tion. The cold is a good ally in pre­vent­ing the spread of this kind of dis­ease.”

Moreover, the expan­sion of water upon freez­ing (by approx­i­mately 9 per­cent) causes micro­c­racks which aer­ate the soil just like it was tilled. If frost lasts for sev­eral days and the process of thaw­ing is slow, this will pro­vide a good water reserve, with­out runoff of organic sub­stance.

“In any case, we must be care­ful that too much snow does not over­bur­den the sec­ondary branches since frac­tures can facil­i­tate the pen­e­tra­tion of Pseudomonas savas­tanoi in more sus­cep­ti­ble vari­eties,” Marsicani con­cluded.

As soon as tem­per­a­tures go back to nor­mal and the ground and the olive trees are dry, we can return to the olive grove and start again with the appro­pri­ate agri­cul­tural prac­tices like prun­ing.