AbstractThe foliar nematode species Aphelenchoides ritzemabosi is reported attacking sweet basil in glasshouses in the province of Imperia, northwest Italy. The nematode colonised and reproduced within the leaf, petiole and stem tissues. The epidermis and mesophyll were invaded by the nematode which caused internerval discoloration and necrosis and collapse of the palisade and spongy parenchyma. All nematode developmental stages, including eggs, were observed in the leaf tissues. Morphology and morphometrics of A. ritzemabosi from chlorotic and necrotic leaf tissues are presented. Possible control measures, which are complicated by the short life cycle of the nematode, the broad host range, and the short productive cycle of basil, are also discussed, together with the risk of an erroneous field diagnosis caused by difficulty in differentiating the symptoms of basil downy mildew and basil black spot from those of the foliar nematode.