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

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.

“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.

“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.

“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