Organic Growers Rely on Traditional and New Natural Methods to Combat Fly

Organic olive grow­ers across the Mediterranean rely on tra­di­tional reme­dies and newly-tested nat­ural meth­ods to con­tain the olive fruit fly, the most per­ni­cious olive tree pest.

The most com­mon prepa­ra­tion is a mix­ture of water, vine­gar and sugar, which is poured into a plas­tic bot­tle with a pierced hole. Attracted by the smells, flies enter but can­not escape, drown­ing in the mix­ture.

“This method, which we learned from grand­fa­ther Ninia, has proven to be very suc­cess­ful,” spouses Vedrana Rakovac and Saša Petković, who pro­tect their 600 olive trees in the vil­lage of Rakovci on the Istrian penin­sula in Croatia, told Olive Oil Times.

Even more orig­i­nal meth­ods were devised by Radoslav Rade Bobanović, which he applies in olive groves in the area of Ravni Kotar, in Dalmatia.

When the fruit is already formed, Bobanović pro­tects it from fly attacks with a kaolin clay, milk and sul­fur solu­tion.

“Milk has a fat struc­ture so that when spray­ing, the mix­ture adheres bet­ter to the fruit,” Bobanović said. ​“It cre­ates a film, a mem­brane, so the pest can hardly see it, and even when the fly sees it, it can’t sting, pierce it.”

Otherwise, each olive fruit fly can lay 250 eggs, one in each fruit. The lar­vae eat the pulp; the fruits are infected, rot and fall. ​“The dam­age can be immea­sur­able. Flies can destroy all the efforts of olive grow­ers,” Bobanović said.

In addi­tion to this, he devised a prepa­ra­tion with horse urine, vine­gar and sugar. ​“Horse urine has a lot of ammo­nia in it, which attracts the olive moth as well as the fly,” Bobanović said.

He and his part­ner Željko Uzelac grow 12,000 olive trees on 45 hectares at the PZ Maslina i Vino in Tinj, along with vine­yards and figs.

“I expect approx­i­mately 40,000 liters of oil, but on the con­di­tion that I win the bat­tle with pests,” said the charis­matic Bobanović.

To this end, he placed pheromone traps and more than 1,000 yel­low bot­tles with the men­tioned prepa­ra­tion all over the olive grove.

Pests enter the bot­tle through a spe­cial open­ing on the side to feed and enjoy. They later drown because they can no longer get out, Bobanović said.

The traps do not kill all pests but sig­nif­i­cantly reduce the olive fruit fly pop­u­la­tion and repro­duc­tion.

Although not sci­en­tif­i­cally con­firmed, this prepa­ra­tion is effec­tive in prac­tice. Ammonia is the basis for nearly all pheromone traps, and horse urine has the most ammo­nia, con­firms agron­o­mist Nevio Colić.

Italian olive grow­ers in organic farm­ing have been using a prepa­ra­tion with salted sar­dine against the olive fruit fly for time immemo­r­ial.

According to Grupa di Coltivazione Biologica, this and other food traps are made from plas­tic bot­tles for min­eral water, 1.5 or 2 liters. These bot­tles are filled up to three-quar­ters with water, and half a salted sar­dine is placed inside.

It is essen­tial to wash the sar­dines well before­hand to remove the preser­v­a­tives and allow the fish to rot.

This putre­fac­tion process cre­ates a hydrolyzed pro­tein com­pound that spreads attrac­tive odors, espe­cially for adult female olive fruit flies.

The attrac­tive­ness of food traps is based on the pres­ence of sub­stances such as putrescine (a poi­son that devel­ops when meat and fish rot), which is known to be very attrac­tive to diptera (insects with two imma­ture wings) from the Tephritidae fam­ily, to which the olive fruit fly belongs.

Adult females, attracted by the unpleas­ant odors devel­oped by putrescine, enter the bot­tle through the open­ing. Once inside, it becomes extremely dif­fi­cult, almost impos­si­ble, for them to find a way out.

Food traps are sim­ple to make at home. Make holes in the upper part of the bot­tle and attach the bot­tle to the tree with a nylon thread with a reg­u­lar cap.

Instead, to improve the effi­ciency of food traps for the mass cap­ture of the olive fruit fly, Italian olive grow­ers have a prod­uct called Trap-trap.

This device, sim­i­lar to a large yel­low plug – yel­low is one of the most attrac­tive col­ors for the olive fruit fly – has a cone that hides a mech­a­nism for hang­ing on a plas­tic bot­tle of min­eral water.

The cone pro­vides suf­fi­cient space for insects to enter through the open­ing in the bot­tle but pre­vents them from exit­ing.

Furthermore, there is a hook at the end of the Trap-trap cap, to which it is pos­si­ble to tie a thread and then hang the bot­tle on a tree. There are also pre-pack­aged traps on the mar­ket with ready-made food bait.

Experts sug­gest that food traps, includ­ing those with salted sar­dines, should be placed on the olive tree’s south or south­west side to achieve opti­mal results.

This site takes full advan­tage of the sun expo­sure and tem­per­a­ture that affects the activ­ity and attrac­tion of the olive fruit fly.

Furthermore, Italian experts sug­gest that plac­ing the traps at a height of one to two meters from the ground is prefer­able to be eas­ily acces­si­ble to the flies.

It is impor­tant to peri­od­i­cally renew the food traps by chang­ing the bot­tle. Generally, chang­ing the bot­tles up to three times is rec­om­mended dur­ing the oil accu­mu­la­tion sea­son, which lasts from July to October.

This main­tains the effec­tive­ness of food baits and ensures that cap­tured flies do not inter­fere with the extra attrac­tion of the traps. Flies trapped inside the bot­tle should be appro­pri­ately dis­posed of and buried in a suit­able place.

However, experts in Italy say that food traps are only part of an inte­grated approach to bio­log­i­cal olive fruit fly con­trol, which may include other mea­sures, such as kaolin clay appli­ca­tion, to ensure ade­quate and com­plete pro­tec­tion of olive trees.

Darko Jakomin also uses the food trap in the clas­sic way in Vanganel near Koper, Slovenia. Only, instead of salted sar­dines, he uses fish heads.

In addi­tion to traps with horse urine, salted sar­dines and fish heads, the newest one with yeast is inter­est­ing.

Researchers from the University of California’s Agriculture and Natural Resources pro­gram con­firmed the effec­tive­ness of the trap devel­oped in Spain called Olipe.

Olipe traps can be made by hand and only require a plas­tic bot­tle with water and a pinch of yeast. In par­tic­u­lar, the Olipe trap con­sists of a plas­tic bot­tle of 1 or 2 liters with 5‑millimeter holes punc­tured on top.

Ongoing research has shown that Torula yeast tablets dis­solved in water are very effec­tive as bait. Traps are set in the shade, and flies are drawn in, where they even­tu­ally drown.

The advan­tage of pro­tec­tion with nat­ural means comes to the fore, espe­cially from the begin­ning of ripen­ing to the har­vest­ing of olives, when the con­di­tions are ideal for a fly attack.

The pit is juicy and full of mois­ture. These phe­no­log­i­cal con­di­tions lead to a soft skin favor­able for bites and the lay­ing of eggs.

At the same time, this is when, in con­ven­tional cul­ti­va­tion, pro­tec­tion with chem­i­cal agents (insec­ti­cides) is time-lim­ited, while in nat­ural cul­ti­va­tion, the described agents can be used from the begin­ning of the grow­ing sea­son until har­vest, that is, through­out the year.