Pest and disease management by intercropping: Suppression of thrips and rust in leek

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Abstract
Leek (Allium porrum L.) is an Important field vegetable in most of western and central Europe. Infestations of onion thrips (Thrips tabaci Lindeman) cannot be controlled with the range of insecticides now available in The Netherlands. Leek rust (Puccinia allii Rudolph) is now also difficult to control. Experiments in which no insecticides or fungicides were applied, were carried out to assess the effects on thrips populations and infection by leek rust when leek crops were undersown with subterranean clover (Trifolium subterraneum L.). To evaluate the economic aspects of this approach, both the quality and quantity of the leeks produced in the two systems were compared. Undersowing leeks with clover drastically reduced thrips infestations which was reflected in improved quality of leeks at harvest. Leek rust incidence was also reduced slightly by undersowing with clover and the quality of the leeks at harvest was also better. Although the quality of the leeks was improved when the crop was undersown with clover, the quantity of crop produced was reduced considerably as a result of plant competition.