Since reduction in effectivity of the bitter wood preparation Quassan in the years 1999 and 2000, the quality of the product had to be criticised. Quality control has since been improved, in so far as each batch is now tested in a biotest on aphids before dispatch. Parallel to its normal use in the field, the effect of Quassan was also field tested in 2001 against apple sawflies. Quassan was tested in different concentrations per hectare and the effect compared with an untreated control as well as with plots treated with a self-cooked Quassiawood extract. All the methods showed an efficacy of 80% or more as compared with the control. Differences due to concentration per hectare used were only minimal
