Articles
INTRODUCTION TO SOIL FUMIGATION AND SPECIFIC PROBLEMS WITH A SPECIAL REFERENCE TO THE EFFECTS OF LOW DOSAGES METHYLBROMIDE ON SOME FUNGI AND NEMATODES
To prevent or control soil-borne diseases, prophylactic measures to avoid the introduction of the pathogen(s) into the cultivated soil, are of primary importance.
When pathogens are already established in the soil, frequently only a disinfection of the soil before sowing or planting can avoid or diminish the risk of heavy losses.
Fumigation of the soil is one of the methods which can be used.
Several chemical compounds, which are active in their gaseous phase, are available.
The situation on a specific holding, viz. host-pathogen combination, soil-type, dimensions of the holding, determines the choice of the application of one of these fumigants.
Much work has been done during the last 10–15 years on the effects of the fumigants, not only in relation to the pathogens involved, but also in relation to dispersal in the soil, degradation of the fumigant, residues in the crops, influence on soil fertility status.
Especially the lastfew years the effects on the environment, viz. pollution of soil, water and air, are studied.
Due to questions about environmental pollution, in 1981 in the Netherlands the amount of methylbromide allowed was restricted to 20 g/m2, applied under a non-permeable plastic sheet.
Research was started on the effects of low dosages of methylbromide, viz. 10, 20, 30 and 40 g/m2, compared to the formerly used high dosage, viz. 125 g/ m2 under permeable cover, on the development and disease incidence of Phytophthora cryptogea on Gerbera and of Pratylenchus vulnus on roses.
In the experiments also other fumigants, viz. metham-sodium, methylisothicocyanate + dichloropropene, and steam disinfection were tested.
In the experiments control of P. cryptogea was best after application of steam or methylbromide, even at a dosage of 10 g/m2. Sufficient control of P. vulnus was only achieved after application of methylbromide, the effects of a low dosage of 20 g/m2 and of a high dosage of 125 g/m2 being equal during the first ¾ year.
Thereafter however the population of P. vulnus in the 20 g/m2 treatment started to build up and quickly reached a damaging level, which did not occur in the 125 g/m2 treatment.