“We have to protect the new lettuce aphid resistance together”

The recent introduction by Rijk Zwaan of lettuce varieties with Nr:0,1 resistance are a major step towards futureproof lettuce cultivation. However, we should not become complacent, according to Rijk Zwaan’s Marco van der Lans: “We need to use all the available tools to protect the resistance.” 

What is your role within Rijk Zwaan? 

“I am Project Leader Quality, meaning I’m involved in all issues related to crop protection. This can include the development of biological seed coatings, the impact of European Union (EU) policies on growers, and biological alternatives to chemicals.” 

How significant is the introduction of Nr:0,1-resistant iceberg lettuces for growers? 

“Nasonovia ribisnigri resistance is a very welcome development. Resistant varieties are one of the most important pieces of the puzzle to ensure futureproof lettuce cultivation. Because currant-lettuce aphids hide deep inside the plant, they are incredibly difficult to control. This is especially the case in iceberg lettuce because of its dense head, meaning that contact insecticides – which have to actually touch the aphids – are not effective.” 

What about the use of systemic pesticides? 

“After the upcoming season, growers in the European Union (EU) will no longer be allowed to use systemic pesticides – which work through the plant’s sap flow – containing Spirotetramat as the active ingredient. Growers are very concerned about the situation. That’s why my colleagues have worked hard to now be able to introduce the Nr:0,1-resistant iceberg lettuce varieties.” 

How important is it to protect this new resistance? 

“It’s essential. Resistant lettuce varieties give growers peace of mind, but we certainly shouldn’t become complacent. The resistance to lettuce aphid biotype 0 held for more than a decade but was overcome in 2007. The resistance to biotype 1 is at an even higher risk of being broken because there are fewer tools at growers’ disposal today. Plus every aphid population has some genetic variation, so there’s always a possibility that the resistance can be overcome. We have to handle this innovation with care.”  

What can growers do to help protect the resistance? 

“My advice is to apply every aspect of the EU’s favoured system: Integrated Crop Management (ICM). That means monitoring pests, using natural predators and biological pesticides, and controlling aphids with the chemical agents that are still permitted.” 

Are growers of open-field crops already using beneficial insects? 

“Not a lot, so far. Much can be learned from organic lettuce growers who are already making extensive use of them. For example, they create flower borders all around the field to attract aphids’ natural predators such as ichneumon wasps, lacewings and ladybirds. Growers can protect many beneficial insects by eliminating broad-spectrum control agents from their spraying schedules. However, this means they might find an insect in their crop occasionally.” 

There’s a lot of knowledge about natural crop protection in the greenhouse sector too, isn’t there? 

“Definitely. The greenhouse sector has built up decades of experience with beneficial insects and how they can be used in combination with chemical or biological insecticides. It makes sense to further develop that knowledge for open-field crops. We need to face facts: crop protection is becoming more complex than before.” 

Why does the EU have stricter regulations than elsewhere? 

“The rules are stricter because there is more debate about surface water quality and the effects of crop protection agents on humans, animals and the environment. The EU is at the forefront of this, but these issues are just as relevant on other continents too. In addition to governments, value chain partners are also taking a critical view of the use of chemical agents. Retailers want fruits and vegetables with the minimum residues possible.”  

What’s your view on the future of lettuce cultivation? 

“Futureproof lettuce cultivation requires effort from every link in the value chain – to protect the resistance, to enable faster evaluation and authorisation of biological agents, and to get people to accept the occasional bug on a lettuce, whether it’s an aphid or a beneficial insect. We really must pull together.”