The use of methyl bromide and carbendazim for the control of lettuce big-vein disease

Lettuce seedlings raised in peat blocks placed on contaminated soil subsequently developed lettuce big-vein disease symptoms when grown in pots of sterilized compost. Incorporation of 0.01 g carbendazim per 4.3 cm³ peat block reduced the number of plants with disease symptoms but did not prevent root infection by Olpidium brassicae , the vector of the big-vein agent. Similar results were obtained when seedlings propagated in the absence of big-vein disease were grown in pots of contaminated soil but carbendazim was less effective when the treated blocks were planted in contaminated field plots. Methyl bromide applied at 500, 750 or 1000 kg/ha temporarily controlled the disease but re-contamination occurred and was complete after three consecutive crops.
Bromide residues in lettuce heads reached 9240 μg/g dry tissue in the first crop but fell to a maximum 772 μg/g by the third crop. Bromide residues in soil fell to natural levels over this period.