Experts Offer Tips on Preparing for the Warm Season in Organic Olive Groves

The warm season corresponds to crucial phases for olive trees. Two experts provided their suggestions for the successful management of the organic olive grove in these conditions.

Riccardo Macari prunes an olive tree.
Jul. 23, 2019
By Ylenia Granitto
Riccardo Macari prunes an olive tree.

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On a sunny July day, we reach the area of the Roman Castles where pruner Riccardo Macari is man­ag­ing an organic olive grove. Today, cooler air pro­vides relief from a heat-wave that has affected Italy for the past cou­ple of weeks.

This warm period fol­lowed the lower than aver­age tem­per­a­tures of April and May, which had partly erad­i­cated some par­a­sites, such as the olive moth (Prays oleae), which still rep­re­sents a threat in some areas,” Macari said. Now, sev­eral grow­ers may have prob­lems with Peacock spot and Anthracnose [caused by the fungi Spilocaea oleaginea and Colletotrichum gloeospo­ri­oides, respec­tively], which dur­ing last win­ter, which was rainy with mild tem­per­a­tures, found favor­able con­di­tions for devel­op­ment.”

The pruner con­sid­ered that those who did not act in time, for exam­ple with cop­per-based fungi­cides, may expe­ri­ence sig­nif­i­cant defo­li­a­tion due to the Peacock’s spot, which is able to move from the old leaves to the new ones.

In some areas, we are still suf­fer­ing last year’s frost dam­age, since the fruc­ti­fi­ca­tion mainly occurs on the branches of the pre­vi­ous year.- Riccardo Macari, Italian olive tree prun­ing cham­pion

Already in February, it was pos­si­ble to pre­dict that humid­ity, given by short rains with higher than aver­age tem­per­a­tures, would have trig­gered these dis­eases,” he said, adding that he treated dif­fer­ent olive groves with cop­per-based prod­ucts con­tain­ing hydrox­ide, oxy­chlo­ride, and above all gly­ci­nate or chelates, which min­i­mized defo­li­a­tion.


After har­vest­ing, in some areas, he imme­di­ately started prun­ing. In olive groves where I had to remove just up to 10 per­cent of the foliage on trees with small diam­e­ters canopies, I started prun­ing soon,” he said. While for heavy trim­ming, as in the case of reform prun­ing which requires work on the main struc­ture of the plant, I waited until the cold and frosts were over, in March.”

However, in late spring of last year, an extra­or­di­nary cold snap hit Italy and other European coun­tries, then it became clear that we need to eval­u­ate the sit­u­a­tion prop­erly to get ahead of the increas­ingly fre­quent extreme weather events.

See Also:Organic Olive Oil

Frost dam­ages can occur if the prun­ing wounds are still open when it freezes,” Macari said. The frost pen­e­trates, break­ing the ves­sels and caus­ing des­ic­ca­tion of the branch or the whole plant. In some areas, we are still suf­fer­ing last year’s frost dam­age, since the fruc­ti­fi­ca­tion mainly occurs on the branches of the pre­vi­ous year. However, even in sum­mer we should take a break from prun­ing, except for young plants under four years.”

In this area, in mid-April, the first mignole’ (in Italian), the inflo­res­cences of the olive trees, popped up. During that period, which is cru­cial, abun­dant rains could be harm­ful as they dilute the pollen, com­pro­mis­ing the pol­li­na­tion and there­fore the fruit set­ting, Macari noted.

As long as the flow­ers were closed, farm­ers could apply Boron-based prod­ucts and bio-stim­u­lants, con­tain­ing pro­teins, amino acids and other sub­stances, to increase the pollen tube. However, Macari sug­gests act­ing well before or after the fruit set­ting.

Immediately after that phase, we can keep the olive moth under con­trol with appro­pri­ate treat­ments,” he said.

During flow­er­ing, a sud­den increase of tem­per­a­tures from 9 degrees Celsius (48.2 degrees Fahrenheit) to 27 degrees Celsius (80.6 degrees Fahrenheit) in the area, along with hot winds in other regions, cre­ated prob­lems for the fruit set­ting. However, a good amount of fruit is now grow­ing, and in mid-July a foliar fer­til­iza­tion can be done to harden the pit.

Then, if it will rain or the tem­per­a­tures drop, we must imme­di­ately mon­i­tor the pres­ence of the olive fruit fly (Bactrocera Oleae) and other pests,” Macari said. The olive moth has three gen­er­a­tion per year, and with appro­pri­ate treat­ments, we shall act on the third gen­er­a­tion.”

Angelo Bo, a Tuscany-based agron­o­mist spe­cial­ized in organic olive farm­ing, gave us other reflec­tions on the veg­e­ta­tive devel­op­ment of the olive tree and the steps to be taken in these months.

The flow­er­ing is a del­i­cate phase that includes the for­ma­tion of the pollen tube,” he said. Then, the pol­li­na­tion is fol­lowed by the fruit set­ting and for­ma­tion. First, we should check the num­ber of flow­ers, then a sec­ond pro­duc­tion con­trol should be made on fruits,” adding that only two to four per­cent of the flow­ers suc­ceed in becom­ing olives.”

Bo remarked that high tem­per­a­tures of up to 38 degrees Celsius (100.4 degrees Fahrenheit) cre­ate prob­lems in fruit set­ting, espe­cially where the devel­op­ment of inflo­res­cences has delayed. However, in some regions, where the flow­er­ing phase started early, May was unfa­vor­able due to low tem­per­a­tures,” he pointed out.

Young olives grow­ing. Photo cour­tesy of Angelo Bo.

Now, with the young fruits on our trees, we must be care­ful and plan mon­i­tor­ing oper­a­tions,” he added, explain­ing that traps for the olive fruit fly should be set up and, depend­ing on the ecosys­tem, fer­til­iza­tion, nutri­tional sup­ple­men­ta­tion, and bio-stim­u­la­tion as well as mon­i­tor­ing of and defense from pests should also all be planned.

In lit­er­a­ture, if the per­cent­age of fruits attacked by the olive moth exceed the thresh­old of 15 to 20 per­cent, based on envi­ron­men­tal con­di­tions, then we can apply an ovi­ci­dal or lar­vi­ci­dal prod­uct,” Bo said, spec­i­fy­ing that a pos­si­ble fruit falling in the sec­ond half of July will be due only to a very small extent to this pest, mainly to other fac­tors, such as nutri­tional imbal­ances, over-load­ing, or re-bal­anc­ing of the plant.

This year, the Sant’Anna School of Advanced Studies of Pisa sug­gested that Tuscan farm­ers act before­hand and set up the traps against the Bactrocera Oleae between the end of June and the first days of July,” he said. In inland areas, this action can be delayed, how­ever, in organic farm­ing, a key fac­tor is to detect in time the start of the flights, and then use repel­lents or adul­ti­cides to pre­vent the egg lay­ing.”

Monitoring of the olive fruit fly can be made with chro­motropic traps, which are adhe­sive sheets whose yel­low color attracts all the Diptera, both male and female, and the pheromone traps, which con­tain the sub­stance that females use to attract the males.

In my opin­ion, the com­bi­na­tion of the two types of traps, in num­ber of two or three per hectare (four or seven per acre) is the best solu­tion to both detect the peak of flights and cap­ture the females for the pur­pose of ver­i­fy­ing their fer­til­ity,” Bo added.

As soon as the first flights are detected, the strat­egy, which may lay down repel­lents, baits or mass traps, should be imme­di­ately pro­ceeded with.

The lat­ter per­form well on plots of at least five to 10 hectares (12.3 to 24.7 acres), while on small sur­faces, we have bet­ter result with repel­lents and insec­ti­cides,” Bo said, adding that it is impor­tant to be atten­tive to the strate­gies used by neigh­bor­ing groves.

If for exam­ple we use mass traps, but sur­round­ing olive groves are treated with repel­lents, there is the risk of attract­ing the flies,” he observed.

Useful repel­lents are cop­per, which has both a caus­tic and bac­te­rio­sta­tic effect, act­ing against the bac­te­ria laid by the flies with the eggs; kaolin-based prod­ucts, which alle­vi­ate the neg­a­tive effects of high tem­per­a­tures; and lime-based prod­ucts with tack­i­fiers that give sta­bil­ity in case of rain.

On the other hand, insec­ti­cides based on com­pounds of the bac­te­r­ial species, Saccharopolyspora spin­ose, which act as adul­ti­cides can also be used. Lastly, if mass traps are used, they should be set up with a den­sity of 150 per hectare (220 per acre). They can be ready-made or eas­ily hand­crafted with a bot­tle con­tain­ing water and sub­stances such as ammo­nia, vine­gar or bicar­bon­ate, along with raw scraps of anchovies or sar­dines.

We should remem­ber that two years ago, the pro­longed heat com­pletely blocked the devel­op­ment of this pest in Tuscany as well as in many other regions,” Bo said. Now, depend­ing on the area and tem­per­a­tures, we must really pay atten­tion to the fly and to the veg­e­ta­tive-pro­duc­tive bal­ance of our olive trees.”

We must be ready to imple­ment emer­gency irri­ga­tion or apply bio-stim­u­lants to limit the water stress in case of drought,” he added

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