Aphid damage poses a major risk for lettuce growers

Aphids peaked early 

There is no doubt in Martin’s mind that this is an urgent problem. Besides being a specialist in iceberg lettuce and Crunchy Cos at Rijk Zwaan, he is also an advisor on open-field crops in North Rhine-Westphalia. When he visited lettuce fields there in mid-June, he even had aphids crawling on his arms. “The aphid peak usually occurs in September, but this year it came early. It affected almost every grower in this region – especially of iceberg lettuce crops, but also of other lettuce types,” Martin explains. 

Huge costs 

The crop specialist knows that an infestation can have severe consequences. “When the aphid pressure is so high, growers simply can’t supply their lettuces to retailers. Consumers won’t accept a lettuce crawling with aphids. Growers have no choice but to destroy their crop. By that time they have already incurred a lot of costs: for renting the land, planting the young plants and applying crop protection agents. Growers question whether they are willing to take such risks again next year,” Martin says, describing the extent of the uncertainty. 

Limited options

Peter Sonneveld, Crop Coordinator Lettuce in northern and central Europe, shares his colleague’s concerns. He explains that Nasonovia ribisnigri is difficult to tackle for all lettuce growers in temperate climates, but is extra challenging for growers in the European Union: “They will no longer be allowed to use systemic pesticides containing Spirotetramat as the active ingredient as of next season.”  

According to Peter, various growers and research institutes have been testing alternatives for aphid control, including biological insecticides and chemical agents that will still be allowed next year, but the results so far have been unsatisfactory.  

“Growers still see too many aphids in lettuces. Not only retailers, but also companies that process and package lettuce are struggling with this issue. They have conducted tests to see whether the aphids can be washed off, but it’s more difficult than expected,” comments Peter.

Finding and crossing in a resistance 

To offer growers an effective solution when the aphid pressure is high, Rijk Zwaan has been working on finding and crossing in a new resistance since 2007, when biotype 1 of the aphid first appeared. “Lettuce varieties with a high resistance against Nasonovia ribisnigri can mean the difference between production and no production,” states Martin, underlining the importance of this work. 

Practical trials of varieties with a resistance trait are currently underway at 20 growers’ facilities in north-western Europe – not only to test the resistance, but also to assess the agronomic traits, says Peter. “These include head shape, base, weight and susceptibility to tipburn.”

A solution for a healthy future 

Martin firmly believes that varieties resistant to the currant-lettuce aphid could really make a difference for growers. “It’s upsetting to see them sometimes having to destroy entire fields of iceberg lettuces. I’m happy that, as the entire Rijk Zwaan team, we are searching for a solution for a healthy future – including for their businesses.”