Efficacy of chemical alternatives for methyl bromide in lettuce production: field experiment.

摘要

In Belgium the production of lettuce is economically very important. The major problems in lettuce production are the plant pathogenic fungi Sclerotinia sclerotiorum (causing lettuce drop) and Rhizoctonia solani (causing bottom rot). These fungi can survive for different years in the soil as sclerotia and can cause serious crop losses. Until January 2006, methyl bromide played a key role in the production of lettuce. However, methyl bromide is phased out as it is an ozone-depleting chemical and alternatives are needed. The chemical alternative should be effective against fungi, weeds and nematodes. Therefore, the efficacy of different fumigants and combinations was tested in a field experiment against fungi, nematodes and weeds. The tested fumigants were methyl bromide (MB), methyl iodide (MI), MI with chloropicrin (CP), metam sodium (MS), metam potassium (MP), 1,3-dichloropropene (DD), dimethyldisulfide (DMDS), dazomet (Daz), DD with Daz, DMDS with Daz, CP and CP with DD. Lettuce was planted 4 weeks (autumn crop) and 27 weeks (spring crop) after disinfestation. In both cultures lettuce weighted more than the control for each treatment, however less significant differences were found during the second one. Almost no significant differences were observed regarding infestation degree of Sclerotinia and Rhizoctonia (only tested in the second culture). This resulted in no significant differences in lettuce drop caused by Sclerotinia. Concerning the efficacy of the different fumigants against fungi in general, only in the first crop significant differences were found, indicating that the efficacy of the fumigants is reduced after 27 weeks. This could also be observed for the efficacy of the fumigants against weeds, where the efficacy of the fumigants was significantly higher during the first cultivation. During the second one less significant differences were found.