Information
Today, we sit down with Sven Paauwe (Sales manager leafy Benelux and Nordics) and Paul Huijs (Product manager Iceberg Europe) to discuss one of the most pressing challenges in leafy produce: Nasonovia ribisnigri. Together, they share their expert perspective on the evolution of this pest, the emergence of the Nr:1 biotype, and how Enza Zaden’s new resistant varieties are helping growers stay ahead.
Paul Huijs: In the leafy produce business, the green lettuce aphid, Nasonovia ribisnigri, has increasingly become a major issue among European producers. Known for its ability to cause significant crop damage, this pest exists in two main biotypes: Nr:0 and Nr:1. While the original Nr:0 biotype could be effectively controlled through genetic resistance, famously introduced in the variety “Dynamite” in 1999, everything changed in 2007. That year, a new biotype, Nr:1, emerged, capable of breaking the resistance that had previously protected crops. Since then, both biotypes have been present in European lettuce fields.
Paul Huijs: The challenge with Nr:1 is that it cannot be distinguished from Nr:0 by the naked eye, yet it overcomes the traditional resistance genes. In response, at Enza Zaden, we initiated an ambitious breeding program, searching for wild lettuce plants that could withstand Nr:1. Through years of classical breeding, marker-assisted selection, and rigorous field testing, we have finally succeeded in developing iceberg lettuce varieties with Intermediate resistance (IR) to Nr:1.
Paul Huijs: The mechanism behind this Intermediate Resistance is multifaceted.
Together, these factors provide a robust, built-in defense system for the crop and, together with other aphid control tools, offer another valuable solution to producers in the fight against Nasonovia.
Sven Paauwe: We obserded very interesting facts during our trials. Firstly, Nasonovia ribisnigri thrives best in cooler climates, with optimal growth and reproduction occurring between 20 and 24°C. However, when temperatures rise above 28°C, the aphids experience high mortality, especially in later nymph stages and adults. At this threshold, reproduction ceases, and fertility in winged forms drops significantly. The critical upper temperature limit for survival lies between 33 and 36°C, depending on the aphid’s form. These findings suggest that climate and environmental conditions play a crucial role in the effectiveness of resistance and the overall pest pressure.
Sven Paauwe: Of course, we encourage growers to try our new Intermediate resistant varieties to be able to assess their performance themselves. Fields that mix resistant and non-resistant varieties can distort the perceived effectiveness of resistance. For the most reliable results, it is recommended to plant larger, uniform areas with Nr:1 IR varieties, as adjacent or related plots can also influence outcomes. Early pest control, especially during the initial period after transplanting, is vital to ensure the crop reaches maturity with strong internal protection.
Paul Huijs: As of now, there is no official protocol for assessing Nr:1 resistance. Each seed company relies on its own expertise and internal evaluations to determine resistance levels, whether high or intermediate. The market for Nasonovia-resistant varieties is still developing, and no comprehensive practical comparison between varieties has yet been made. For Bremia resistance, by contrast, the independent organization IBEB-EU oversees guidelines and testing, but such oversight does not yet exist for Nasonovia.
Sven Paauwe: We have successfully launched four new iceberg lettuce varieties with Intermediate Resistance to Nr:1, also featuring Full Bremia resistance (Bl: 29–41) and HR Nr:0. Larger seed volumes will be available from mid 2026, supporting commercial sowing from June onwards. We encourage growers to already discuss their interests with their local representatives to ensure proper positioning and maximize the benefits of these new varieties.
If you’d like to learn more about our solutions and ongoing research, please visit our dedicated website: Nasonovia Resistance.
For tailored advice or to discuss how our IR Nr:1 iceberg varieties can benefit your business.
We encourage you to reach out to your local Enza Zaden sales representative today.