“There is no solution yet”: a pest fly worries fruit producers

“There is no solution yet”: a pest fly worries fruit producers
“There is no solution yet”: a pest fly worries fruit producers

Dn the five-hectare orchard covered with an immense net by Laurent Reynard, the cherries are brilliant red, still firm, large in size. They are especially spared from Drosophila suzukii, a small devastating fly against which the industry is seeking “all-out” solutions.

This insect from Asia was detected in France in 2010. It particularly attacks red fruits still on their branches, laying its eggs there.

The sector began in 2012 to find a solution and the quest intensified with the ban on chemical pesticides, dimethoate in 2016 and phosmet in 2023, explain officials from the Association of Environmental Protection Organizations. producers (AOP) Cerises during a press visit organized in Mazan, in Vaucluse.

The products still authorized are much less effective, they assure.

In 2023, when the weather was particularly favorable for the spread of the fly, the production of AOP members fell by 35% compared to the average of the previous five years, assures the general director of the organization, Alexandra Lacoste. The installation of ultra-tight mesh nets, in a single block over an entire orchard or by row of cherry trees, provides a satisfactory response.

Unexpected bonus: the nets provide protection against hail and wind, they create shade in the event of extreme heat and require the height of the trees to be limited, making the work of seasonal workers easier.

Laurent Reynard saw the difference: the cherry orchard on the slopes of Ventoux above which he installed a net in 2021 “gives a yield of 20 tonnes per hectare, compared to 6 to 7 tonnes in general”, he says.

But this operation has a cost. Laurent Reynard paid 98,000 euros to cover 5 hectares of a flat, rectangular orchard.

Prices rise depending on the height difference or exposure to the wind and on average, it costs 80,000 euros per hectare, according to Jean-Christophe Neyron, president of AOP Cerises. Less than 10% of cherry producers have equipped themselves with nets, according to Alexandra Lacoste.

The creation of a microclimate under the mesh can also encourage other pests, and does not eliminate another harmful insect, the Rhagoletis cerasi or cherry fly, which spends the winter in the soil.

The hope of ganaspis

The sector is also looking for biocontrol solutions. Aliénor Royer, engineer at the Interprofessional Technical Center for Fruits and Vegetables, tests each year several products offered by companies which are currently considered not effective enough or too expensive.

Essential oils ? In the laboratory, the results are interesting, but “they are very sensitive to UV and a lot of applications would be needed,” explains the engineer.

Splashing white clay on the tree prevents the insect from recognizing the fruit. But “there is still no solution for cleaning the cherry afterwards”.

Yeasts, bacteria, “we are looking in all directions,” assures Aliénor Royer. In the medium term, the industry is banking heavily on a parasite, ganaspis.

Failing to have found local species in France capable of harming Drosophila suzukii, researchers went looking for them in 2015 in Japan, the fly’s area of ​​origin.

After seven years of laboratory work, they obtained authorization to release ganaspis in five experimental areas, explains Nicolas Borowiec, specialist in biological control methods against invasive pests at the National Research Institute for Agriculture, l food and the environment (INRAE).

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