Monitoring Anthonomus rubi damages in raspberry fields

Abstract: The strawberry blossom weevil Anthonomus rubi Herbst is an important pest in openfield raspberry crops of Switzerland. In certain fields more than 30% of flowers are attacked bythe weevil and damaged flower buds do subsequently not bear fruits. Today growers tend toapply systematically insecticides against this pest, although several provisional economicthresholds for intervention are proposed, e.g. 1 female per linear row metre or 1 to 5% clippedflower buds per inflorescence. However, many part-time growers do not monitor adultpopulations by beating raspberry plants, since it is judged to be too complicated. The visualassessment of the number of flower buds damaged is an alternative, but it is also time consuming.In order to simplify the process, we used the Nachmann function to study the relationshipbetween the number of clipped flower buds per inflorescence and the percentage ofinflorescences damaged. We obtained an excellent correlation (r2: 0.91) between these twoparameters using a long-term data set collected on different floricane-fruiting cultivars. Thecurrent threshold of 1 to 5% of clipped flower buds corresponds to 10 to 35% of inflorescenceshaving at least one bud damaged. Thus, this novel method reduces significantly the time forassessing damage and it should consequently offer an effective alternative to the systematicapplication of insecticides.