Slug control by molluscicide and herbicide application prior to planting iceberg lettuce

摘要

Control of slug damage is difficult in lettuce, where the presence of slugs, faeces, damage or slug pellets is unacceptable in harvested produce. A replicated factorial field experiment is described where metaldehyde pellets and glyphosate herbicide were applied singly or together, in mid February 2002, to plots on land that had been ploughed in December 2001 prior to planting Iceberg lettuce in early. May 2002. Mild wet weather through May and June permitted slug numbers and activity to increase asthe crop matured, especially on untreated plots. Under these conditions, the treatments applied in mid February had valuable effects in significantly reducing slug damage close to harvest by 64% for molluscicide and 74% for herbicide used alone and by 91% for both used in combination. These benefits were achieved despite overall applications of molluscicide pellets to the lettuce crop. Slugs found in damaged lettuce heads were almost all small juvenile Deroceras reticulatnm, which were probably eggs orneonates when the experimental treatments were applied. It is therefore thought that the treatments reduced the number of eggs laid by D. reticulatnm adults and survival of juveniles present at or hatching shortly after the time of treatment. The juvenile slugs in lettuce heads had survived pellet application to the growing crop, probably because juveniles were unlikely to come into contact with pellets in this crop.