Mini‐plot field experiments using the rhabditid nematodePhasmarhabditis hermaphroditefor biocontrol of slugs

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Abstract
The nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench in two outdoor mini‐plot field experiments to test the capacity of the nematode to protect Chinese cabbage seedlings and wheat seeds from damage by the field slug Deroceras reticulatum. The first experiment compared a single dose of nematodes (2 X 1010 ha‐1) with methiocarb pellets added at the recommended field rate (5.5 kg.product ha‐1 ) and untreated plots. Plots treated with either nematodes or methiocarb pellets had significantly less slug damage than untreated plots and, from the third week onwards, there was significantly less slug damage on plots treated with nematodes than on methiocarb‐treated plots. At the end of the experiment, 6 weeks after treatment, both slug numbers and biomass were significantly higher in untreated plots than in either methiocarb‐treated or nematode‐treated plots. In the second experiment, six nematode doses ranging from 1 X 10 8 to 2 X 1010 ha‐1 were compared with a standard rate application of methiocarb pellets and untreated plots. Plant protection improved with increasing nematode dose between 1 X108 and 8 X 108ha‐1, but showed little or no further improvement at higher doses. Plant protection similar to that given by methiocarb pellets was provided by nematode doses of 8 X 108 ha‐1 and above.