Apple sawfly (Hoplocampa testudinea, Klug) situation, forecasting, monitoring and use of extract from Quassia amara for controlling the apple sawfly in organic apple orchards in Sweden

Abstract: The main objective of the thesis was to find out the growers’ perspective towards the problem of apple sawfly (Hoplocampa testudinea, Klug) as well as its solution, evaluate the suitability of Dutch and Swiss forecasting methods in Swedish environment, and evaluate the efficiency and timing of Quassia extract application with varying concentration of rapeseed oil product Zence 40 against the apple sawfly. The apple sawfly was monitored using white sticky traps in two orchards located in Alnarp and Malmö. The forecasting models for emergence of first sawfly (Dutch model) and egg hatch (Swiss model) were combined and used for determining timing of Quassia extract application. The model worked well for forecasting both the first emergence and egg hatch of the apple sawfly. A field trial was conducted for spraying Quassia extract as a control measure against the apple sawfly. The treatments were 1) Petal fall (PF), 2) Day degree low zence (DDL), 3), Day degree high zence (DDH) and 4) Control (C). The dose of Quassia was used at 12 kg per hectare in 400 liters of water. The percentage of the apple sawfly damage was significantly lower in all treatments compared to control with 3.8%, 3.2%, 2.9% and 9.9 % damage in treatment 1, 2, 3 and 4. There was no difference in secondary damage between treatments. This could have been influenced by a large aphid infestation at that time. Semi structured face to face interviews were carried out to get deeper understanding of the problem. Older orchards were found to have relatively more infestation compared to new orchards. The growers were interested to continue the work with monitoring and trap catches in the coming season. They wished that the model should be proposed which can be used by the advisors from Äppelriket and the Board of Agriculture for forecasting the apple sawfly in Sweden.