• The technology centre is providing walnut growers with a quick-reference guide on how to deal with Rhagoletis completa
• The pest, which has caused losses of up to 80 per cent in some areas of northern Spain, has been spreading in the Basque Country for the past three years

 

The walnut husk fly (Rhagoletis completa) has become the main plant health concern for walnut growers in the Basque Country. This insect damages the green husk of the fruit, causing it to turn black and making it difficult to shell later on, which reduces the commercial value of the harvest, even though the inside of the walnut remains in good condition. Over the last three years, losses have reached 80 per cent in the worst-affected areas of northern Spain, including Catalonia, Galicia, Asturias, Cantabria and the Basque Country. Following the successful technical seminar held on 26 March in Lantarón (Álava), NEIKER has produced a practical guide setting out the most effective strategies for controlling the pest, with clear and accessible information for anyone who grows walnut trees.

 

A practical guide for those living with the pest

The guide structures the control strategy around three critical stages in the insect’s life cycle. The first involves capturing adults using baited traps before they lay eggs. The second recommends the use of repellents from the moment the first insects are caught in the monitoring traps, with a maximum of one week to set them up. The third stage involves treating the soil with entomopathogenic microorganisms – that is, natural microbes such as fungi or bacteria that attack and eliminate the insect larvae without harming the environment.

‘This guide is part of our commitment to providing accurate information in a timely manner to all walnut growers who are concerned about this pest,’ says Amaia Ortiz Barredo, head of NEIKER’s Department of Plant Production and Protection.

 

A monitoring programme for the whole of the Basque Country

The publication of this guide forms part of the monitoring programme launched by NEIKER in 2026. The network comprises 16 monitoring points spread across Álava, Bizkaia and Gipuzkoa, in collaboration with the three Provincial Councils and the Añana Regional Development Agency (ADR). Based on this data, the research team will issue weekly alerts on the pest’s population dynamics.

The initiative also involves a network of participating farmers. This enables the effectiveness of four different integrated pest management strategies to be assessed in the field. The aim is to generate applied knowledge, tailored to the climatic and agricultural conditions of the Basque Country.

 

Download the guide and keep up to date with the latest developments regarding the pest

The guide is available to download free of charge in spanish via the following link: