Phasmarhabditis hermaphrodita is a lethal slug parasitic nematode that has been formulated into an effective biological control agent called Nemaslug®. We investigated the possibility of using different application methods of P. hermaphrodita to reduce cost and the number of nematodes applied. We also compared P. hermaphrodita with a new slug pellet called Ferramol®, which is available for use on organic farms

Rae, R G

Robertson, J F

Wilson, M J

English

Organic Eprints

Aspects of Applied Biology 79, 2006What will organic farming deliver?  COR 2006211Organic slug control using Phasmarhabditis hermaphroditaBy R G RAE, J F ROBERTSON & M J WILSONUniversity of Aberdeen, School of Biological Sciences, St. Machar Drive, AB24 3UU, Aberdeen, Scotland, U.K.Summary  Phasmarhabditis hermaphrodita is a lethal slug parasitic nematode that has been for-mulated into an effective biological control agent called Nemaslug®. We investigated the possibility of using different application methods of P. hermaphrodita to reduce cost and the number of nematodes applied. We also compared P. hermaphrodita with a new slug pellet called Ferramol®, which is available for use on organic farms.Keywords: Phasmarhabditis hermaphrodita, Deroceras reticulatum, metaldehyde, iron phosphate  Introduction  Phasmarhabditis hermaphrodita is a lethal parasite of many slug species (Wilson et al., 1993; Speiser et al., 2001; Iglesias & Speiser, 2001; Grewal et al., 2003) and has been formulated into a biological molluscicide that is produced by Becker Underwood (Littlehampton, UK) and sold under the trade name Nemaslug®. It has been used successfully to protect a range of crops against slug damage including arable crops (Wilson et al., 1995), high value crops such as asparagus (Ester et al., 2003a) and the potential use in ﬂ  oriculture has been demonstrated using Orchids (Ester et al., 2003b). We investigated using different applications of P. heramphrodita to reduce the number of nematodes applied and the cost. To do this we used three split applications of a lower dose compared to one broadcast application of P. hermaphrodita. We also examined the effectiveness of combining P. hermaphrodita and a new iron phosphate based slug pellet (Ferramol®, Neudorff GmbH, Germany), which has just been released for use in the UK.Materials and MethodsMini-plot experiments  Twenty-four boxes (0.7 × 0.5 × 0.2m) were half ﬁ  lled with fresh topsoil. Eight Chinese cabbages (Brassica rapa var. pekinensis) were planted in each. The recommended rate of P. hermaphrodita (30 cm-2, 150,000 in total) was applied to six boxes. A lower dose of P. hermaphrodita (5 cm-2, 25,000 in one application) was applied to another six boxes. This treatment consisted of three low dose applications at two week intervals so that the total number of nematodes applied was exactly half the recommended rate. Nematodes were suspended in two litres of water and applied using a watering can ﬁ  tted with a rose. Six boxes received only water and acted as the control 212and six received the recommended rate of Metarex® green (0.8 g m-2) metaldehyde pellets. Eight Deroceras reticulatum slugs were added to each box. They were supplied with a shelter to provide protection during daylight hours. All sides of the boxes were coated with Fluon® (Sydmonson, 1993) and ﬁ  tted with a layer of copper fencing to prevent slugs migrating from the boxes. Slug damage was recorded every week for six weeks as percentage damage per leaf. Effect of combinations of iron phosphate and P. hermaphrodita  Eighteen seed tray propagators were ﬁ  lled with top soil. Five four-week-old Chinese cabbage were planted in each. There were ﬁ  ve treatments, which consisted of: no nematodes and no mollus-cicides, P. hermaphrodita, metaldehyde, iron phosphate (5g m-2 as Ferramol®), P. hermaphrodita and iron phosphate. Each treatment was replicated three times. Five D. reticulatum were added to each propagator and were provided with shelter. Propagators were ﬁ  tted with plastic lids lined with copper tape and ﬁ  tted with air holes. Once the slugs were added, the propagators were sealed and placed in an incubator at 17oC with a 12-hour light and dark cycle. Percentage damage to each leaf was assessed 1, 2, 4, 8, 12, and 16 days after treatment. Data analysis  Data were recorded as percentage damage per week and analysed using Kruskal Wallis and Tukey’s pairwise comparision to assess differences between treatments.ResultsMini-plot experiment  All treatments were signiﬁ  cantly different from the control from week two onwards (P ≤ 0.05) (Fig. 1). The recommended rate of nematodes and low dose only differed signiﬁ  cantly on weeks 4 and 5 (P ≤ 0.05). The recommended rate of nematodes and metaldehyde did not differ signiﬁ  -cantly after week 3 (P ≥ 0.05). Metaldehyde was signiﬁ  cantly more effective than the low dose throughout the experiment (P ≤ 0.05).Fig. 1. Mean percentage damage to Chinese cabbage leaves exposed to Deroceras reticulatum.Effect of combinations of iron phosphate and P. hermaphrodita  Metaldehyde, iron phosphate and nematodes and iron phosphate provided signiﬁ  cant protection against slug damage after day four (P ≤ 0.05) (Fig. 2). Nematodes applied at the recommended rate provided poor slug protection and only signiﬁ  cantly differed from the control after day 12. Metaldehyde, iron phosphate, and nematodes and iron phosphate did not differ signiﬁ  cantly throughout the experiment (P > 0.05).0102030405060708090Week 1 Week 2 Week 3 Week 4 Week 5 Week 6TimeMean percentage damage per leafControl Recommended rate of nematodes 3 x Low dose of nematodes Metaldehyde213Fig. 2. Mean percentage damage of Chinese cabbage leaves exposed to Deroceras reticulatum treated with iron phosphate, metaldehyde, nematodes or nematodes and iron phosphate.Discussion  P. hermaphrodita applied three times at a lower rate provides signiﬁ  cant protection against slug damage. These results are in agreement with Ester et al. (2003a) who also found that repeated applications at lower doses provided signiﬁ  cant protection against slug damage in asparagus. Applying half the recommended rate and achieving slug protection represents a substantial decrease in cost thus making nematode treatments more attractive to growers.  The combination of P. hermaphrodita and iron phosphate provided as good protection against slugs as metaldehyde. For organic growers in the UK., who are at a distinct disadvantage as they cannot use molluscicides such as metaldehyde or methiocarb, nematodes and iron phosphate shows massive potential. For example, by using iron phosphate, larger slug species that are resistant to nematodes will be killed and any slugs present in the soil will be killed by the nematodes. In order to conﬁ  rm these results further research will focus on large-scale ﬁ  eld trials. Acknowledgements  The authors wish to thank John G Skea and Sons, and Stewart Jamieson for their kind collabora-tion with this study, and the Kintail Land Research Foundation who provide ﬁ  nancial support to the organic programme at the University of Aberdeen.ReferencesEster A, Rozen Van K, Molendijk L P G. 2003a. Field experiments using the rhabditid nematode Phasmarhabditis hermaphrodita or salt as control measures against slugs in green asparagus. Crop Protection 22:689–695.Ester A, Rozen Van K, Hazendonk A. 2003b. Efﬁ  cacy of pesticicides to control Lehmannia valentiana (Férussac) in orchids (Cymbidium) in greenhouse experiments. In Slugs and Snails: Agricultural, Veterinary and Environmental Perspectives, pp. 89–94. Ed. G Dussart. Alton, Hants: 010203040506070Day 1 Day 2 Day 4 Day 8 Day 12 Day 16TimeMean percentage damage per leaf ControlNematodesMetaldehydeIron phosphate214British Crop Protection Council.Grewal S K, Grewal P S, Hammond R B. 2003. Susceptibility of north American native and non-native slugs (Mollusca: Gastropoda) to Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae). Biocontrol Science and Technology 13:119–125.Iglesias J, Speiser B. 2001. Consumption rate and susceptibility to parasitic nematodes and chemical molluscicides of the pest slugs Arion hortensis s. s. and A. distinctus. Journal of Pesticide Science 74:159–166.Speiser B, Zaller J G, Newdecker A. 2001. Size-speciﬁ   c susceptibility of the pest slugs Deroceras reticulatum and Arion lusitanicus to the nematode biocontrol agent Phasmarhabditis hermaprodita. Biocontrol 46:311–320.Symondson W O C. 1993. Chemical conﬁ  nement of slugs: an alternative to electric fences. Journal of Molluscan Studies 59:259–261.Wilson M J, Glen D M, George S K. 1993. The rhabditid nematode Phasmarhabditis hermaphrodita as a potential biological control agent for slugs. Biocontrol Science and Technology 3:503–511.Wilson M J, Glen D M, George S K, Hughes L A. 1995. Biocontrol of slugs in protected lettuce using the rhabditid nematode Phasmarhabditis hermaphrodita. Biocontrol Science and Technology 5:233–242.

Organic slug control using Phasmarhabditis hermaphrodita

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