Field test using the nematode Phasmarhabditis hermaphrodita for biocontrolof slugs in Spain

An experiment was carried out between May and July 1999 in Galicia (North-W est Spain) to test the capacity of the nematode Phasmarhabditis hermaphrodi ta to protect Weld grown lettuces from slug damage in our Weld conditions. The experiment compared a single dose of nematodes (3 x 10(9) ha(-1)) with mini-pellets containing 5% metaldehyde, applied at the recommended Weld rat e (3 g pellets m(-2)), and untreated plots. Slug damage for each lettuce he ad was estimated on six dates during the first 4 weeks after planting. At h arvest, each lettuce head was weighed, scored as marketable or not by weigh t and external aspect, and inspected for slugs. Metaldehyde significantly r educed slug damage to lettuce plants from the first day after planting to t he third week. Nematodes significantly reduced slug damage from the second to the third week. At harvest, 6 weeks after planting, the mean weight of t he lettuce heads and the number of marketable heads in the nematode plots w ere as good as in the metaldehyde plots, and both treatments were significa ntly better than the untreated plots. The number of slugs within the harves ted plants was significantly reduced only with the metaldehyde treatment.