"Growers are very concerned about the climate and shrinking crop protection product range," begins Paul Huijs, Leafy Vegetables Product Manager at Dutch breeder Enza Zaden. "You can use breeding, which we're investing heavily in, to respond to some diseases. We hope to combat as many diseases as possible with resistance."
Enza Zaden is, for example, working hard on an iceberg lettuce that is resistant to Nasonovia aphids. "Many lettuce varieties are highly resistant to Nasonovia 0, but the mutant Nasonovia 1 is most troublesome. There are currently no commercial varieties on the market with that resistance. We should be able to introduce Nasonovia 1-resistant iceberg lettuce within two years," says Paul.
Less effective chemicals
Nasonovia 1 has been around since 2009. Paul, though, notes that it has become a bigger problem in the past few years. He attributes this to the declining range of crop protection products. "Nasonovia 1 wasn't an issue for several years because those chemical products were quite effective. However, there are fewer and fewer of those products on the market, and some remain less effective. Nasonovia 1 aphids are, thus, becoming more prevalent in cultivation. The decline in the number of active substances will likely continue, too, making it increasingly difficult to use chemical methods to control a number of pests."
There are a few crop protection products that can help combat the Nasonovia problem. That has recently caused cultivation issues in the Netherlands and Germany but can also strike elsewhere in Europe. However, according to Paul, that solution is only temporary. "Those products can provide support for another three years or so, which offers time to develop other solutions," he says.
Impact on acreage?
Not finding solutions to Nasonovia, but also, for instance, Bremia - a fungal disease that causes lettuce leaves to turn yellow or brown - the product manager foresees consequences for the market. "There's currently enough lettuce on the market. But if the cultivation risks become so great in the next five years and are borne solely by growers, that could impact the acreage." He also sees a role for consumers. "People have a reasonable zero tolerance for damage to lettuce. Shoppers will have to have greater acceptance if lettuce can no longer be supplied without that zero damage guarantee," Paul explains.
He believes the process must, therefore, be broadly implemented, including in research. "It takes seven years for a lettuce variety to be ready. That means that, for instance, the Bremia genes incorporated seven years ago must work against physiotypes that occur seven years later. So, research is important, and we've gathered a great deal of knowledge in this area in recent years."
Combination
Paul sees potential in combining measures. "In the future, you may have to supplement resistance with a biological solution to achieve sufficient control," he explains. That is why Enza Zaden is also taking part in Koppert Biological Systems' research into using chrysopa in lettuce cultivation. "That involves using lacewing eggs, from which larvae emerge that feed on aphids. That method is already widespread in greenhouse horticulture and is now used in open-field lettuce cultivation, too."
Paul adds that the European lettuce acreage has been stable lately. Iceberg and Romaine lettuce are the largest crops, supplemented by smaller segments such as full-soil butter and colored lettuce. That means a sizable market is eagerly awaiting the resistant varieties. "All the more because all those types of lettuce are susceptible to Nasonovia and Bremia," he concludes.
This article was previously published in Primeur May 2025. Click here for the link to the entire edition
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Enza Zaden
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