The clubroot disease causes considerable yield losses in the cultivation of Brassica vegetables. At an experimental site with an elevated infection pressure of the clubroot disease and with a pH-value of 6.8 calcium cyanamide and quicklime were tested for their preventive effect against this soil-borne disease in white cabbage crops in 2007 and 2008. Calcium cyanamide was applied 3 weeks before planting followed by a supplementary application 2 weeks after planting with certain procedures. Ground quicklime was applied 10 days before planting and incorporated into the upper soil layer between 0 and 30 cm. Calcium cyanamide, even if applied at high rates of 1000 and 1500 kg/ha, suppressed the clubroot disease only to a limited extent. A strategy including 2 applications both before and after planting did not increase the suppressive effect of calcium cyanamide against the clubroot disease. Ground quicklime applied at a rate of 100 dt/ha led to an increase of the pH-value beyond 7.7 staying at this level until the middle of the growth period of the crop. Probably in consequence of this the high rate of 100 dt/ha applied quicklime contributed to a decreased infection level of the roots and to a significant increase in cabbage yield. From these latest results, it can be concluded that the effectiveness of calcium cyanamide is limited at sites with an elevated infection pressure of the clubroot disease, whereas finely ground quicklime efficiently prevents this soil-borne disease even under such conditions.
Preventive effects of different fertilization strategies against the clubroot disease (Plasmodiophora brassicae)