Abstract
A field experiment was conducted in Mitaka City, Tokyo on the use of converter furnace slag and fungicide treatments to control clubroot disease in broccoli. A field area (8 ares) infected by Plasmodiophora brassicae was divided into amelioration and control plots. The amelioration plot received 100 tons per hectare of converter furnace slag; both plots received 4 fungicide treatments (no treatment, quintozene, fluazinam and flusulfamide). Broccoli seedlings were then transplanted to all plots and cultivated for 3 months. The soil pH (H_20) of the amelioration plot was 5.9 before slag application, 7.5 before broccoli transplantation and 7.9 after harvesting. Clubroot disease incidence in the control plot (no slag, with fungicide) was 90%; very serious damage to the broccoli was recognized. The control plot clearly showed the effects of fungicide use, but disease incidence could not be decreased below 30%. In the amelioration plot, by contrast, disease incidence decreased to 20% in the no-fungicide plot and to 10% in the fungicide-treated plot. The boron content in broccoli leaves from the amelioration plot was about twice that in the control plot, despite a soil pH above 7. There were no differences between amelioration and control plots in terms of broccoli leaf manganese, vitamin-C or reducing sugar content. The above results indicate that converter furnace slag is very effective in controlling clubroot disease, and can help reduce fungicide use on farmland.
