Impact of crop rotation and soil cultivation on the development of pests and diseases of rapeseed

Reducing the probability of damage induced by pests and diseases is a main issue of 'Integrated Pest Management' (IPM). The effects of crop rotation a nd soil cultivation on decay of plant debris, inoculum of Sclerotinia scler otiorum and the incidence of diseases in a subsequent rapeseed crop were in vestigated in various field experiments over several years. The impact of t illage techniques on the mortality of rape stem weevil (Ceutorhynchus napi Gyll.) as well as on parasitoids of cabbage stem weevil (Ceutorhynchus pall idactylus (Mrsh.)) and pollen beetle (Meligethes aeneus F.) hibernating in soil of rape fields was evaluated by comparing the number of soil-invading larvae with the number of hatching adults in the following spring. Rapeseed plant debris decayed faster after being chopped up and shallowly i ncorporated into the soil. Survival of sclerotia of S. sclerotiorum was enh anced when the inoculum was buried deeply by ploughing. Non-inversive tilla ge after rapeseed cropping enhanced the formation of apothecia in the first year, however, it strongly decreased the occurrence of apothecia in che se cond and third year. The type of soil cultivation significantly affected th e hatching race of parasitoids of cabbage stem weevil and pollen beetle. Pa rasitoids were damaged more severely by stubble cultivation with subsequent ploughing than by reduced-tillage with rotating harrow or especially by di rect seeding. The hatching rate of rape seem weevil was only increased on p lots after direct seeding. Under the experimental lay-out used, no signific ant effect of crop rotation and soil cultivation on the incidence of diseas es and pests in the subsequent rapeseed crops could be found.