Lettuce: Evaluating aphid control strategies

Currently in the UK, lettuce root aphids are effectively controlled with neonicotinoid seed treatments (imidacloprid, Gaucho and thiamethoxam, Cruiser), which also provide control of foliage feeding aphids for many weeks after transplanting. However, depending on the lettuce variety and its planting density, the seed loading is adjusted so that the maximum total dose of neonicotinoids per hectare per year is not exceeded. This has shown that varieties such as Little Gem, which are planted at higher densities using lower seed loadings (e.g. Gaucho - 80 g/ha), are still protected from aphids. Therefore, growers could reduce their pesticide usage and associated costs if they could lower the seed loading of other varieties planted at lower densities such as Iceberg (Gaucho -120 g/ha commonly used) without increasing the risk of aphid infestation, particularly lettuce root aphid. In addition, seed treatments can be associated with phytotoxicity problems but methods to reduce these negative effects, e.g. dummy pills, are not widely used due to concerns about their unknown residue levels.

Prior to the use of neonicotinoids, lettuce root aphid was a significant problem particularly near areas with poplar wind breaks when control measures were not used. However, since the use of seed treatments lettuce root aphid has been effectively controlled and no further research has been conducted to identify alternative chemicals which could be used instead of seed treatments. Information about alternative chemicals would allow growers to diversify their aphid control strategies. Furthermore, due to the imminent restrictions on using neonicotinoids on crops attractive to bees, identifying alternative chemicals would be useful for growers should further restrictions be imposed on the use of neonicotinoid seed treatments.

The aim of this project is to determine and compare the persistence and efficacy of currently used seed treatments, seed treatments with lower loadings, dummy pills, spirotetramat (Movento) and other new systemic chemicals for the control of lettuce root aphid and a foliage feeding aphid, the currant-lettuce aphid. This information can be used by growers to inform future aphid control strategies and may reduce the use of pesticides and their associated costs.