METHYL BROMIDE AS A SOIL FUMIGANT FOR CONTROLLING SOIL-BORNE PATHOGENS AND CERTAIN OTHER ORGANISMS IN VEGETABLE SEEDBEDS

Abstract

The effectiveness of methyl bromide (Dowfume MC-2, 98% methyl bromide and 2% chloropicrin) as a fumigant for controlling diseases in seedbeds used for the production of vegetable seedlings under glass was studied. A differential response of the microfloral components of a sandy loam compost soil to the lethal action of methyl bromide was observed. In general, fungi were destroyed at lower concns. than were bacteria and actinomycetes. Of the pathogenic fungi tested, Fusarium oxysporum f. niveum and a Fusarium sp. causing root decay of onion seedlings were the most resistant to the lethal action of methyl bromide. Whereas the former was destroyed by a dosage of 1.5 lb. per 100 cu. ft. in sandy loam soil and the latter by a dosage of 2 lb. in muck soil, Pythium sp. Rhizoctonia solani, and several other pathogenic fungi were destroyed by a much lower dosage, namely, that of 0.6 lb. per 100 cu. ft. Bacteria showed a broader range of variability than the fungi in their tolerance of methyl bromide. Whereas Xanthomonas vesicatoria and Rhizobium trifolii were destroyed at dosages of 1-2 lb. per 100 cu. ft., Pseudomonas tomato occurring in the soil were not destroyed at dosages of 4 lb. per 100 cu. ft. The benefits derived from the fumigation of a sandy loam compost soil with methyl bromide were reflected not only in the freedom of vegetable seedlings from disease but also in their increased and uniform growth. Some vegetables showed greater growth in fumigated than in steam-sterilized soil, whereas others showed opposite effect.