The graph below shows ‘day-degree forecasts’ for currant-lettuce aphid (Nasonovia ribisnigri) and lettuce-root aphid (Pemphigus bursarius). The forecasts for both aphid species are based on accumulated day-degrees (D°) from 1 February (base 4.4°C). The information was collected in projects funded by the AHDB, Defra and LINK.

In the study on currant-lettuce aphid, the mean numbers of day-degrees accumulated until the first aphid was found and until peak numbers of aphids were found were 507D° and 935D° respectively. Comparisons between observed and predicted dates showed that this forecast is likely to be accurate to within a 2-3 week period.

In the study on the lettuce-root aphid, the start of the migration of winged aphids from poplar to lettuce occurred after 672D° had been accumulated since 1 February. Monitoring data collected during the project were compared with this forecast, which was shown to give adequate early warning of the start of aphid migration.

Forecasts updated 13 July 2022