BIOFUMIGATION WITH BRASSICA JUNCEA PELLETS AND LEEK MATERIAL IN CARROT CROP ROTATIONS

Biofumigation denotes the use of plant material to treat fields infected with soil borne diseases or nematodes. The plants are usually Brassica species such as B. juncea, Sinapis alba or Raphanus sativus, but also Allium species have been used. The principle in biofumigation is that the plant material is macerated and incorporated into the soil where it releases toxic substances. In Brassica species these are mostly isothiocyanates that are liberated from glucosinolates by an enzymatic process. In Alliums the toxic substances are various sulphides liberated after maceration and incorporation. In two carrot fields infected with carrot-cyst nematodes (Heterodera carotea) and various fungal diseases, experiments with application of Biofence^® (pellets of dried B. juncea) and leek (Allium porrum) material were carried out. The Biofence (3 t/ha) and leek material (100 t/ha) were incorporated (early April) into the soil (top 15-20 cm) in a randomised block design with three replicates. Control plots with no biofumigation were treated as for other plots. All treatments were carried out with or without plastic covering immediately after incorporation. Nematode concentrations in the soil were recorded prior to, and 2 weeks after treatment. After 2 weeks from treatment, plastic coverings were removed and carrots (cultivar ‘Bolero’) were sown in all plots. At harvest, around early November, the plot soil was again analysed for nematodes. Approx. 80 kg of carrots from each plot were cool stored (1°C and >95% RH) until March next year, when the degree of fungal storage diseases (Sclerotinia, Phytium, Rhizoctonia, Rhexocercosporidium, Mycocentrospora, Streptomyces) was assessed. No significant effect of either Biofence^® or leek material on the number of live nematode in soil samples at carrot harvest could be detected. The incidence of fungal diseases in March on the stored carrots also did not show any significant effects of the biofumigation treatments.