AbstractThe growth and yield increases in red raspberry that followed the repeated application of the systemic fungicide benomyl in field-plot studies in Scotland in 1970-75 were not due to the suppression of invertebrate pests. Benomyl had little effect on the numbers of aphids and nematodes, which, anyway, were insufficiently abundant to cause damage. Benomyl did, however, decrease the earthworm population. In the following years, when benomyl was no longer applied, significantly more canes died from midge blight in the plots that had been treated most frequently with benomyl than in those that had not been treated. This was probably a consequence of increased infestation by larvae of Resseliella theobaldi (Barnes) in the benomyl-treated plots because the fungicide increased the extent of cane splitting and hence the number of oviposition sites for the midge.