march 2013 slug control FACT SHEET NORTHERN, SOUTHERN AND WESTERN REGIOns slug ideNTificaTiON aNd MaNageMeNT in the higher rainfall zones where zero till and stubble retention is practiced, slugs are an increasing problem. as no single control method will provide complete protection, an integrated approach is best. australian growers spend an average Pest species KEy Points $8.7 million annually on slug control. The main pest species in australia are the The incidence of slugs has increased grey field slug and the black keeled slug, but slugs need moisture and shelter with changes to cropping practices. the brown field slug has also been recorded to thrive. cool wet summers and cultivation and stubble-burning previously an abundance of stubble provide kept numbers down, but the widespread in high numbers. More than one species ideal conditions. adoption of minimum till and stubble may be present within a single paddock. Moisture availability is a key retention has provided slugs with more grey field slug or reticulated slug regulator of slug populations. favourable habitat. (Deroceras reticulatum) surface-active slug species such as the The grey field slug, or reticulated grey and brown field slug find crevices in The grey field or reticulated slug is slug, and black keeled slug are the the soil during dry summer conditions to 35 to 50 millimetres long and light grey to main pest species, but brown field avoid heat and drying out. They emerge slugs can also pose a serious threat. fawn in colour with dark brown mottling. when conditions are moist to breed and There are up to three generations a year. No single control method will be feed. grey field slugs are most active at it will generally breed in autumn and spring, completely effective; an integrated temperatures between 4°c and 20°c. however, if conditions are favourable this approach is needed. life cycle species will breed any time – a pair can produce up to 1000 eggs a year. it is slugs are a major pest of crops globally, slugs are hermaphrodites, therefore, both mainly surface active and is a major pest and have emerged as a serious pest for individuals of a mating pair lay eggs. of crops and pastures. australian grain growers in recent decades. They will breed whenever moisture and attacks on emerging crops can cause temperature conditions are suitable – Black keeled slug (Milax gagates) major economic losses, even when slug generally from mid-autumn to late spring. The black keeled slug is 40 to 60mm long numbers are relatively low. each pair will lay eggs in batches. and black or brown with a ridge down slugs will eat all parts of a crop plant, eggs are laid in moist soils and will hatch its back. This species can burrow up to however, seedlings are the most vulnerable within three to six weeks, dependent 20 centimetres underground to escape and this is the time when major economic on temperature. Juveniles look like smaller the heat. it is more problematic in drier losses can occur. versions of the adult. environments, such as south australia, a gRdc report, The current and potential PHOTO: Mic although it is widespread throughout south- costs of invertebrate pests in grain crops, eastern and Western australia. a breeding (see useful Resources) has found that in H pair can lay up to 200 eggs a year. terms of economic loss, slugs are the sixth ael Nas most damaging invertebrate pest for the Brown field slug (Deroceras australian grains industry, costing on average H panormitanum) $25.9 million in lost production across wheat, barley, oats and canola crops annually. The brown field slug is 25 to 35mm long, slugs are present in all major grain growing The eggs of the black keeled slug, laid and usually brown all over with no distinct regions of australia. They pose the biggest in a clod of moist soil. Slug eggs hatch markings. it is mainly surface active but threat to growers in the southern and within three to six weeks. A pair of black can burrow to shallow depths. it is more western regions, but are also a significant keeled slugs can lay up to 200 eggs common when pasture is a frequent part of problem for growers on Queensland’s per year, but some species are able to the crop rotation. a breeding pair can lay south eastern darling downs. produce up to 1000 eggs per year. up to 500 eggs per year. level 1, Tourism House | 40 Blackall street, Barton acT 2600 | PO Box 5367, Kingston acT 2604 | t +61 2 6166 4500 | F +61 2 6166 4599 | E [email protected] | W www.grdc.com.au The black keeled slug can burrow up PHOTO:s Mic to 20cm underground to escape the PHOTO: Mic heat and so it survives well in drier The grey field or reticulated slug is a major pest of Australian grain crops and pastures. environments. Its burrowing behaviour H It is 35 to 50mm long and ranges from light grey to fawn in colour with dark brown H also allows it to attack germinating ael Nas ael Nas mottling. Under favourable conditions, this species will breed any time. A pair can seedlings underground, making damage produce up to 1000 eggs a year. difficult to detect. H H Hedgehog slug (Arion intermedius) at the break of season, monitor for the slugs present. To counter this, sample more presence of slugs. The most effective time than 10 refuges per 10 hectares. a significant pest species in europe and to bait is at sowing, followed by rolling New Zealand, the hedgehog slug has been Where unexpected crop damage is to consolidate the seedbed. However, recorded in a number of high-rainfall (more occurring, inspect the area after 10pm this cultural practice may not fit with a than 600mm) locations. it is up to 25mm on a mild, calm night. zero-till operation, so assess the scale of long and grey in colour with a yellow foot. it the problem and make the management as well as looking for slugs, check for other is distinguished by its breathing pore at the decision appropriate to your operation. pests such as european earwigs or beetles front of the mantle (the section at the front that could cause similar damage. of the slug that covers the internal organs). Baits are most effective when paddocks are bare, so if there is retained stubble, control When monitoring is not practical from a crop damage may not be as good. time or resource perspective, an alternative option is to put out lines of bait to gauge slugs can be underestimated as pests during the winter months, continue to populations, especially in areas where slugs because they are nocturnal and shelter monitor for any plant damage during occurred previously. during dry conditions, and therefore are not crop emergence. Repeat baiting may be generally visible during daylight hours. required during crop establishment. Baiting control methods They will attack all plant parts but seedlings in spring is generally not effective because effective control involves a combination of are the most vulnerable crop stage and can there are ample alternative food sources. measures: chemical, cultural, and biological. suffer major economic damage. in Queensland, seedling canola, soybeans Populations as low as one grey field slug and sunflowers are the crops at greatest chemical control per square metre can inflict severe damage risk, particularly on creek flats where there Baiting is still the only chemical control option. on a canola crop at establishment. is zero till and overhead irrigation. apply baits after sowing and before crop grey and brown field slugs are mainly Monitoring emergence to protect emerging seedlings. surface active, requiring moist refuges at Three types of baits are registered for the the soil surface such as volunteer crop The foundation of any iPM program is control of slugs. plants and broadleaf weeds. monitoring, but accurate estimation of slug numbers is difficult because slugs are hard to 1. Baits based on metaldehyde (there are Black keeled slugs are a burrowing species, find, populations are often clumped and their many products available), some of which and can feed directly on germinating seed. This activity is dependent on moisture availability. often makes damage more difficult to detect are registered for all slugs and some for compared to the surface-feeding species. One monitoring method is to create surface grey field slugs only. Metaldehyde is a refuges in the form of terracotta paving schedule 5 poison and is highly toxic control approaches tiles, carpet squares or similar. These can to birds and mammals. spread evenly give an indication of slug activity and the and avoid heaping to avoid attracting No single method will provide complete relative number of slugs present. a 300mm off-target animals. control so an integrated pest management by 300mm refuge represents approximately (iPM) approach is required. 2. Baits based on methiocarb (Mesurol®), 1m2 when soil moisture is favourable (more which is registered for all slugs. than 25 per cent). concentrate monitoring By understanding the system’s complexity Methiocarb is highly toxic to carabid and working on pest control year round, a on areas where slugs have been a problem beetles, one of the few predators of reasonable level of control can be achieved. in the previous autumn in order to assess slugs in australia and New Zealand, population activity, especially after rainfall. in the summer months, remove refuges by which it kills by secondary poisoning. controlling weeds and managing stubble check the refuges early in the morning, 3. a bait based on iron edTa complex through grazing. as slugs seek shelter in the soil as it (Multiguard®), which is registered gets warmer.