During four consecutive years of experiments with carrots in monocrop and undersown with subterranean clover (Trifolium subterraneum), it was shown that intercropping significantly reduced root damage by the carrot rust fly (Psila rosae) and by cavity spot (Pythiumspp.). Differences between a standard variety and a carrot rust fly ‘tolerant’ variety were found. Good yields in quality and quantity could be obtained. Possible causal mechanisms of the observed intercropping effects are discussed.