Workshop on the Phase-Out Plan for Phosmet: Alternative Control Methods and Biological Control

Laurent Ruck, a research officer at Terres Inovia, presented an overview of the presence of large flea beetles in rapeseed fields. “This pest is present throughout the country. After a quieter fall in 2024, adult flea beetles caused damage to rapeseed crops in the fall of 2025 in certain regions,” he explains. This is especially true given that the pressure from flea beetle larvae in the fall and early winter of the current growing season (2026) is greater than in previous years.
  

However, flea beetles have developed strong resistance (SKDR mutation), and pyrethroids—the only authorized insecticides—are no longer effective. This mutation is spreading. “In cases of strong resistance, the only solution against leaf damage caused by adults is early sowing and emergence to reach the 3–4 leaf stage around September 15–20, the date when flea beetles generally colonize rapeseed fields.” Against the larvae, the only alternative is Minecto Gold, which is authorized only under an annual exemption.
 

Biocontrol strategies were studied as part of the Phosmet Phase-Out Plan:
• Fatty acid salts: these act by dehydration and suffocation and must come into direct contact with the flea beetle.
• Sulfur: this appears to have a repellent effect.
•    Several products with physical barrier properties were evaluated, such as talc, kaolin, and chabazite. Among these three solutions, kaolin applied with a wetting agent proved to be the most effective, but its efficacy was not superior to the previous solutions and it could present certain application constraints. Other physical barriers must be evaluated, and the impact of adding a wetting agent must be assessed.
 

We must now identify new modes of action to test under varying pressure conditions and better understand the application conditions conducive to their effectiveness. Work continues with new solutions being evaluated in the PARSADA Altifast project. However, the biocontrols evaluated have not proven effective for managing larvae.
  

With currently available products, this approach is considered unrealistic; therefore, trials for direct control of larvae are not being continued. However, avenues developed by the Plan’s research projects are paving the way for new modes of action against this target, such as predatory mites (MOPLAH project).
 

This project sought to identify deterrent plants and study the underlying metabolites. Industrial sourcing of deterrent molecules was conducted using a Sinapis alba matrix by screening extracts for their deterrent properties, followed by the whole plant. Following this work, a candidate deterrent molecule derived from a wild Brassicaceae plant was selected and then validated in the field through six trials.
  

For the white mustard extract, “the activity of a candidate glucosinolate on the whole plant, at a rate of 1 kg/ha, was validated by obtaining an extract containing the deterrent glucosinolate at a maximum concentration of 10%. “The industrial production cost of this extract exceeds €300/kg,” concludes Thomas Rey of INRAE.
  

For the candidate deterrent molecule, formulation work will continue to optimize field efficacy.
  

"This project aimed to 'optimize the application of a biocontrol product to reduce larval pressure from large flea beetles and integrate the product with technological tools,' explains Théophile Kazmierczak of Alvie. A combined solution using a biocontrol product was tested."
  

The benefits of the proposed combined solution include:
  

• Keep pest larval populations below economic damage thresholds to protect yields and reduce financial losses for farmers.
• Enable farmers to prioritize high-risk fields, thereby improving resource allocation, reducing stress, and enhancing the quality of decisions.
• Improve advisors’ technical expertise and the relevance of their recommendations, allowing them to focus on priority tasks.
• Continuously record field data to enable gradual improvements in the solution’s positioning and effectiveness.
    

“In the traditional growing regions of Central France, Eastern France, and Southwestern France, the terminal bud weevil has been observed in more than 8 out of 10 plots. It has developed resistance to pyrethroids, the only insecticides currently authorized,” noted Laurent Ruck, a development engineer at Terres Inovia.
  

Two areas were focused on:
• Gaining a better understanding of the biology and ecology of the terminal bud weevil: the goal was to describe how the insects colonize plots and the time elapsed before the first egg-laying to improve the timing of direct control measures. Trials provided a better understanding of how the reproductive system evolves over time to better understand the pest’s life cycle.
•    Improving risk assessment at the plot level: despite the trials conducted as part of the Phosmet Phase-out Plan, the results available to date are insufficient to update decision-making guidelines regarding whether or not to intervene against the terminal bud weevil in high-risk regions. Further trials with varying infestation levels under contrasting agronomic conditions are still needed. This work is continuing within the PARSADA Coleofast project.
  

“Parasitoids are effective natural enemies that help control pests over the long term,” says Céline Robert, a research officer at Terres Inovia.
 

To protect them, it is recommended to “limit tillage after a rapeseed crop and, when using insecticides, follow the decision-making guidelines and avoid spraying in the middle of the day, during periods of parasitoid activity.”
 

It is also important to preserve refuge areas (field edges, hedges, etc.) and manage field edge mowing carefully (one mowing per year, with straw removal in the fall if possible).
  

To promote connectivity between semi-natural areas, large plots should be avoided.