Field experiments using the rhabditid nematode Phasmarhabditis hermaphrodita or salt as control measures against slugs in green asparagus

Abstract

Green asparagus ( Asparagus officinalis L.) crops are frequently damaged by the grey field slug ( Deroceras reticulatum). Most damage occurs in the soil, although some asparagus spears are attacked above ground. In the Netherlands damage occurs especially during the first 5 weeks of harvesting, from the end of April until the end of May and results in loss of quality. Field experiments were carried out from 1998 until 2000 at Oudkarspel in the western region of The Netherlands with the objective of controlling slugs with the slug-parasitic nematode ( Phasmarhabditis hermaphrodita) and common salt (sodium chloride (NaCl)). Nematodes and salt were applied as row applications in asparagus beds. Dosages of 10,000–600,000 nematodes per m 2 were used. Salt was applied in doses of 500–4000 kg NaCl per ha. Each of the treatments was applied from 1 to 4 times and was compared with conventional field application of metaldehyde pellets (0.35 kg a.i. per ha) in an equal number of applications and with untreated plots. Significant protection of the crop was achieved with nematodes during the harvest period in 1999 and 2000, when nematodes were applied three times in the row at a dose of 50,000/m 2 (2000) or 100,000/m 2 (1999 and 2000). Additionally, salt applied at 2000 kg/ha twice (1998) or at a dose of 1000 kg applied four times (1998, 1999 and 2000) provided successful slug control. An application of slug-parasitic nematodes (Nemaslug ®) is recommended once at a dose of 300,000/m 2 or three times at a dose of 50,000/m 2 as a row application for control of slug damage in green asparagus in The Netherlands.