How to combat Drosophila suzukii in 2024: the CTIFL guide

Take the time before the season to think about possible strategies to implement in each plot on the farm, based on:

• Knowledge of the biology of D. suzukii.
• D. suzukii pressure (traps, BSV information, etc.) from the previous season.
• Potential harvest dates.
• Possibility of using on-farm prophylaxis methods.
• Mode of action, efficacy and pre-harvest intervals (PHI) of registered specialities.
• Existing complementary methods (see section III).
• The environment around the plot: woods, wetlands, etc.

Protection against Drosophila suzukii must be implemented from the beginning of veraison. All varieties are susceptible to attack. The strategies implemented must be able to respond to the specific situations in the orchards.

Different maturity groups require different protection strategies

All ripening windows require protection against D. suzukii, which should be implemented as soon as the first signs of colouring appear. In general, in-season varieties are subject to the greatest pest pressure, because the climate favours the development of Drosophila and because of the synchronisation between ripening and the flight curve. However, the other ripening windows should not be neglected:

• Early varieties, in years when the flight of Drosophila suzukii intensifies in spring, as in 2022, require specific protection for this earlier pest.
• Late varieties, for which the protection period is longer, may have a higher risk due to the short cycle of D. suzukii, which allows for further generation. In general, late varieties are given at least one additional treatment compared to early varieties.

NB: In case of very high D. suzukii pressure (detection of the first damage in the plot or in neighbouring plots), it may be useful to apply an adulticide product after the first harvest. In this case, only a product with a 3-day ARD (see tables on page 5) can be used to ensure a second pass.

Keeping abreast of D. suzukii population levels in the field and environment

It is necessary to monitor population trends in order to detect early flights and, if necessary, implement control measures. To do this:

• Consult the Bulletins de Santé des Végétaux (BSV) (phytosanitary bulletins) of your area to know the real-time situation and the expected evolution. The ecophytopic platform refers to the available BSVs: BSV base search engine | Ecophytopic
• The placement of traps in plots, combined with regular fruit observation, can detect the return of D. suzukii in crops and, if necessary, trigger the implementation of protection measures. Protection should be implemented as soon as the first insects and damage appear in the field. Monitor D. suzukii pressure by installing monitoring traps. Traps can be made at home from a simple red plastic bottle with a hole. The most commonly used attractant for monitoring D. suzukii is a solution consisting of one part water, one part apple cider vinegar and one part red wine, plus a few drops of unscented dishwashing detergent. The contents of the trap are emptied into a bottle once a week. The attractant solution is then replaced. It is best to store the captured insects in the liquid, which must be kept in a cool place until it can be observed.

One caveat: once the fruits are ripe in the orchard, the insects are more attracted to them than to the trap. The correlation between trapping levels in a plot and the level of damage has not been proven.

Focus on prophylaxis

Everything possible must be done to prevent the insect from spreading in orchards. The implementation of prophylactic measures generally improves the situation. It is therefore recommended to:

• Since D. suzukii likes cool, moist environments, ensure that the orchard is well ventilated (prune trees accordingly, keep grass short, avoid standing water in the orchard, etc.). Anything that promotes moisture should be avoided.
• Be vigilant and adjust harvest dates according to the stage of ripeness of the fruit, to avoid over-ripe fruit remaining in the plot, which can be a source of inoculum. Likewise, do not leave unharvested fruit on or near the plot.
• Remove sorting waste from the plot and dispose of it carefully to avoid contamination or population development (e.g. place sorted fruit in airtight bags or in a bin covered with a dark coloured cloth and leave it in the sun for a week (solarisation).

Characteristics of products authorised for use against fruit flies on cherry trees (including Drosophila suzukii and Rhagoletis cerasi)

The following table shows the products with a permanent marketing authorisation:

The following table shows the products for which a 120-day AIC application was obtained in 2024:

To consult the list of 120j AdGs.: http://agriculture.gouv.fr/produits-phytopharmaceutiques-autorisations-de-mise-sur-le-marche-dune-duree-maximale-de-120-jours. For all authorized products: https://ephy.anses.fr.

Several efficacy tests were carried out on some of the products mentioned, which allowed us to derive their efficacy range:

• Between 70% and 80%: EXIREL (cyantraniliprole) and SOKALCIARBO (kaolin)
• Between 60% and 70%: KARATE ZEON (lambda cyhalothrin)
• Between 40% and 60%: SUCCESS 4 (spinosad) and DELEGATE (spinetoram)
• Between 20% and 40%: NATURALIS (Beauveria bassiana)

The efficacy ranges are given as a guide, and application of the products does not guarantee similar results. Climatic conditions may affect the effectiveness of the solutions: for example, under hot and dry conditions, NATURALIS (Beauvaria bassiana) is less effective.

Examples of phytosanitary treatment routes based on these commercial products are described in treatment guides (e.g., the guide to rational and biological protection "South Arbo 2024") or can be consulted by supporting organizations.

Protection strategies implemented in the field must be adapted to the specific conditions of each orchard. To limit the risk of resistance development, it is recommended to alternate the active substances used.

In 2023, the CTIFL launched a trial to evaluate protection strategies. The results are available on the CTIFL website: https://www.ctifl.fr/comparaison-de-strategies-utilisables-en-agriculture-conventionnelle-et/ou-en-agriculture-biologique.

Six strategies were compared, two of which can be used in organic farming. These strategies are based on products available with perennial marketing authorization or 120-day marketing authorization in 2023.

Efficacy evaluations were carried out on the two flies on the fruits: Drosophila suzukii and Rhagoletis cerasi. The efficacy of the evaluated strategies ranged from 61% to 97%, while the untreated control showed 30% damage. These results were obtained with respect to the soil and climatic conditions and pest pressure specific to the test plot. Application of these strategies does not necessarily guarantee equivalent results to those obtained.

Other methods of protection

Physical protection with networks (monorang, monoparcelle or peripheral)

The effectiveness of protection with nets (monorang and monoparcelle) has been demonstrated in cherry orchards. With totally 'watertight' nets (alt'droso mesh, without holes, with good joints on the ground or around trunks), the effectiveness is 100%. A change in climate has been observed under single-cell nets (higher temperatures at warmer times and higher relative humidity in the absence of wind).

Although nets require a significant investment, in the current context of gradual withdrawal of active substances, they are the most effective means of protection. They are easiest to install in new plantations, although goblet orchards can be adapted.

A word of warning: their installation alters the technical itineraries of the orchard and particular attention must be paid to the possible appearance of other pests: aphids, mites, etc.

The effectiveness of perimeter nets is variable and limited depending on the sites and years of experimentation. Netting alone does not provide sufficient protection for orchards: its effectiveness in the 18 trials ranged from 0 to 66%. This type of net is still being studied together with other partial effect levers.

Use of mass trapping

The objective of mass trapping is to capture large numbers of D. suzukii in and around crops to reduce damage. Mass trapping systems have been studied for D. suzukii. To date, these systems have not proved effective in trials conducted in France on cherries and strawberries under high pressure conditions when used alone.

The date of placement of the traps seems to play an important role in the results obtained: if they are placed too late (less than 28 days before harvest), they are ineffective. Conversely, if traps are placed early (at least 45 days before harvest), there is a clear benefit in most situations.

In 9 trials conducted between 2019 and 2021 with massive traps placed more than four weeks before harvest, TRAP DECIS, added to grower strategies, was on average 42% more effective than grower strategies without traps. The break time of this trap was about 3 hours per hectare and did not require reloading of the attractants.

The following table shows the traps with permanent marketing authorisation:

Biological control with parasitoids

Native parasitoids

Several species of native Drosophila parasitoids were studied in order to identify parasites capable of controlling D. suzukii. Of the five species studied, only one was selected: Trichopria drosophilae. This pupal parasitoid showed the most interesting parasitism rate in the laboratory. Tests on cherry trees showed that the parasitoid has little resistance to the climatic conditions of south-eastern France.

In orchards where parasitoids have been introduced, the application of insecticides may impair the development and thus the action of T. drosophilae.

Exotic parasitoids

After several years of laboratory studies, the parasitoid Ganaspis cf. brasiliensis has been shown to significantly reduce the population of D. suzukii three weeks after its introduction. It is also the most specific parasitoid for this fly. The application for authorisation to introduce the parasitoid was obtained in August 2022. The first introductions of the parasitoid were made in September and October 2023 in different regions of France on behalf of INRAE.

Further releases and post-introduction monitoring will take place in 2024. This means of protection still needs to be studied before it can be applied by producers.

Protection methods under study

The Drosophila suzukii project, financed by the French Office for Biodiversity (OFB) and led by CTIFL in collaboration with INRAE, started in January 2024 and will last three years. All research topics are included in the project: knowledge of the fly, the evaluation of protection methods (synthetic and biocontrol products, biological control, new application methods, physical control, sterile insect technique), work on varietal leverage and the creation of the most suitable plots for D. suzukii management.

Other funded projects complement the search for solutions, such as the Plan alternatives d'urgence phytosanitaire fruits et légumes (2023-2025) and the STRATOS project (2024-2027).

Source: Protection des cerisiers contre Drosophila suzukii, Éléments techniques à prendre en considération en 2024, Note de synthèse - Cahiers Environnement-Sécurité, 04/2024, CTIFL, https://www.ctifl.fr/protection-des-cerisiers-contre-drosophila-suzukii-elements-techniques-a-prendre-en-consideration-en-2024.

Cherry Times - All rights reserved