Non-chemical methods of agrophage control have gained increasing popularity recently, and particular attention has been paid to enhancing biodiversity in agrocenoses. Intercropping, i.e. growing of two or more crops (onions, carrots, dill, beans, Lacy phacelia, mustard) simultaneously in the same field, reduces pest infestations. The rationale behind intercropping is that different crops planted together act as attractants for beneficial insects (hoverflies, ladybirds) and effectively disorientate the pests (aphids, carrot flies) which are then unable to find host plants. This study was conducted in the Experimental Garden of the University of Warmia and Mazury in Olsztyn, in the growing seasons of 2009–2010. The experiment was established on brown soil of quality class IV b, and ridges were prepared in line with the generally observed standards of organic farming. The first experimental factor were six carrot cultivars differing with respect to the growth and development period: ‘Deep Purple F₁’, ‘Florida F₁’, ‘Interceptor F₁’, ‘Joba’, ‘Kazan F₁’ and ‘Purple Haze F₁’. The second experimental factor were three methods of carrot fly biocontrol, compared in the following treatments: control – unprotected plants, the application of the biocontrol agent Bioczos BR containing paraffin-coated garlic pulp (10 g cubes), carrots intercropped with dill cv. ‘Szmaragd’ and carrots intercropped with Welsh onions cv. ‘Parade’. Carrot-dill and carrot-Welsh onion intercropping effectively reduced damage to carrot roots caused by carrot fly larvae. The applied biological control methods had a significant effect on carrot yield. The application of Bioczos BR and carrot-Welsh onion intercropping had a beneficial influence on the total and marketable yield of carrot storage roots. Carrot-dill intercropping resulted in a significant yield decrease. The content of dry matter, total sugars and L-ascorbic acid in carrot roots was affected by the cultivar and the cultivar × biocontrol method interaction. Higher concentrations of dry matter and L-ascorbic acid were noted in carrot cultivars with purple-colored roots, ‘Deep Purple F₁’ and ‘Purple Haze F₁’. The average nitrate content of carrot storage roots did not exceed the maximum permissible levels set out in the Regulation of the Minister of Health.

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