As Pesticide Bans Loom, Croatian Agronomists Advise Other Methods to Stop the Olive Fly

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Olives are attacked by more than 250 pests, but the olive fruit fly (Bactrocera oleae) is by far the most dan­ger­ous.

The flies can destroy all the efforts of olive grow­ers and dam­age the entire crop. Namely, each female lays an aver­age of 50 eggs, leav­ing one egg on each drupe.

As there are three or more gen­er­a­tions, immea­sur­able dam­age is pos­si­ble not only for the cur­rent har­vest but for the fol­low­ing one as well.

As a result, a grow­ing num­ber of pro­duc­ers are turn­ing to pest man­age­ment pro­fes­sion­als to help them pro­tect their trees and liveli­hoods.

Among the prob­lems fac­ing grow­ers is a lack of appro­pri­ate insec­ti­cides that may be used in the groves. The European Commission banned dimethoate in 2019, the future of phos­met is uncer­tain and the fly’s resis­tance to deltamethrin has already been proven.

In the future, olive grow­ers have fewer insec­ti­cide options to which to turn.

The Croatian Ministry of Agriculture has said it will pro­hibit the sale of Imidran (phos­met) after May 1 and its use after November 1. The min­istry will also pro­hibit the sale of Insegar (phe­noxy­carb) after May 31 and its use after December 31.

Starting in 2023, the min­istry will begin mon­i­tor­ing olive fruit for resid­u­als of the two pes­ti­cides and take puni­tive actions against those who keep using them.

However, Josip Ražov, a bio­con­trol tech­ni­cal expert at Syngenta, an agri-tech firm, said it is pos­si­ble to pro­tect olive groves with­out these prod­ucts.

New solu­tions are being devel­oped in the form of inte­grated con­ser­va­tion strate­gies, one of which is the use of traps for mass cap­ture. Ražov said Syngenta’s Karate Trap B is one of the newest con­trol meth­ods now avail­able in Croatia.

According to Syngenta, this trap is a ​“mas­sive cap­ture device for the con­trol of the olive fly using the attract and kill tech­nique, com­posed of a spe­cific attrac­tant, a trap com­posed of a base and lid with insec­ti­cide.”

Ražov said this is the only trap on the mar­ket that is rec­om­mended for use right now and stands on the tree year-round, until next spring.

The olive fruit fly is already present in the groves, he warned. Therefore, he argued that these traps should be set up even before the flies have enough food on the olive trees.

Ražov added that the high­est num­bers of trap cap­tures are recorded in the spring until the onset of high tem­per­a­tures, and in the autumn dur­ing and after the har­vest.

As a result, the trap that is present in the olive grove all year has greater poten­tial to catch and reduce the pop­u­la­tion, and thus sig­nif­i­cantly reduce dam­age.

Ražov said the more it is used on a larger sur­face and over sev­eral years, the bet­ter the result, which is why he rec­om­mended set­ting the trap in early May and using it until next spring.

Other types of traps intended for the mass catch method, which are cur­rently on the mar­ket (Eco Trap, Super Track) also are good mod­els that have proven effec­tive in com­bat­ing flies but are not designed for year-round use.

Instead, these traps are installed about a month to two days before har­vest and do not last one year.

Croatian agri­cul­tural asso­ci­a­tions also rec­om­mend using traps, regard­less of the design, on as large an area as pos­si­ble to achieve the best results.

It is also very impor­tant to con­trol the fly in this way by plac­ing traps in home gar­dens in urban areas that are gen­er­ally not pro­tected, and are a breed­ing ground for the pest.

However, set­ting up and mon­i­tor­ing these traps can be costly. To that end, Ražov reminded grow­ers that they may apply for IACS mea­sure 10.1.12 and receive up to €293 per hectare of aid.

Along with using the traps, Ražov said other types of inter­ven­tions may be made before the har­vest. For exam­ple, grow­ers can also spray kaolin, an alu­mi­nosil­i­cate soft white min­eral, or an approved insec­ti­cide.

Marijan Tomac, an agron­o­mist, fur­ther rec­om­mends that grow­ers use Success Bait, pro­duced by AgroChem Mak, ​“to hunt olive flies en masse, regard­less of whether they have olives in organic or con­ven­tional pro­duc­tion.”

Success Bait, in addi­tion to insec­ti­cides (spin­osad), con­tains an agent that attracts flies and is very effec­tive in con­trol­ling the olive fly before it lays eggs on the fruit.

By mon­i­tor­ing the ele­vated pres­ence of adult olive flies, sev­eral Success Bait treat­ments may be per­formed dur­ing July, August and September.

In the period from August to the begin­ning of September, a 3‑percent solu­tion of Success Bait is usu­ally applied to the olive trees three times.

The treat­ment pro­ce­dure itself is as fol­lows. Several lower branches on the south side of the olive grove are treated. A cer­tain num­ber of trees on the edge of the olive grove are selected or every other tree in the edge rows is treated. All trees in every other row can be treated.