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Field studies were conducted to evaluate brassicaceous amendments in combination with solarization against diverse soilborne organisms in cut-flower production systems. Across a diversity of California climates, the application of broccoli (Brassica oleracea var. botrytis) did not consistently reduce populations of Fusarium spp., citrus nematode (Tylenchulus semipenetrans), or weeds. Solarization in combination with broccoli amendments did not consistently improve pest suppression in cool coastal regions, whereas solarization was an important component of suppression in the hot central valley. When the biomass of broccoli was increased from 4 to 8.4 dry tons/ha, there was a decrease in survival of weeds and citrus nematode but the effect on Fusarium spp. survival was not consistent. A horseradish (Armoracia lapathifolia) amendment reduced nematode populations compared to broccoli, but increased field bindweed (Convolvulus arvensis L.). Our research demonstrates that soilborne organisms vary greatly in their susceptibility to brassicaceous amendments. The citrus nematode was consistently suppressed by brassicaceous amendments, while the effect on Fusarium spp. and weeds was variable. To achieve consistent and reliable pest suppression in amendment-based management systems, it is essential to determine and understand the component mechanisms active against specific soilborne organisms. Accepted for publication 10 October 2003. Published 20 November 2003.

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