Slugs have recently emerged as being a significant problem in soybean seedlings on the north coast. The Beat Sheet also reports that they have been found on other pulse crops in northern NSW/southern Queensland areas (see: http://thebeatsheet.com.au/general/slugs-in-seedling-crops/). Slug activity has probably increased due to the continual wet conditions combined with the minimal till practices used so widely. The retained stubble is a source of food and shelter for young slugs and snails. However, populations of Carabid beetles and predatory earwigs among other predators will also be in greater abundance under these stubble retention conditions and growers have reported seeing very large numbers of active Carabid beetles in their crops in the evenings, see image below. For this reason it is important to consider a slug bait that has minimal impact on these predators eg. the iron phosphate/EDTA complex baits such as Multiguard. The other options are based on Metaldehyde which can be less effective in humid conditions as they work by dehydrating the slugs to the point of death, however if conditions are very humid the slugs may survive.
The Beat Sheet have recommended a monitoring regime based on management recommendations by consultants in southern states where slugs are traditionally more of a problem.
See: http://thebeatsheet.com.au/general/slugs-in-seedling-crops/. Further information regarding control can also be found on that site.
Caution: Metaldehyde baits are very toxic to mammals and birds and if used, should be spread evenly to avoid heaping which will attract wildlife and dogs. The iron chelate complexes are less toxic to mammals and birds although questions have been raised about the toxicity to dogs of these compounds. – please take care.
Biological options based on nematodes are registered for use against slugs in Europe where slugs are traditionally more of an issue. Although nothing biological is registered in Australia, work is being done to develop a biological option. Interestingly, Janelle Dowley, President of the North Coast Oilseed Growers Association has observed and sent to The Sweep Net what looks like a (naturally) nematode infected slug.
If people find abnormal looking slugs please send them into The Sweep Net. Otherwise, slugs can be sent to Michael Nash at CESAR, Bio21 Institute, Melbourne University, 30 Flemington Rd, Parkville Victoria 3010. Ph: (03) 83 442 521. If a GPS coordinate can be supplied with this it would be helpful to Michael who is aiming to build up a slug incident database for species which are causing problems in NE Australia. If sending slugs, healthy or infected, please post them in a jar with moist paper, and a little bit of plant food. A location (GPS coordinates if possible), please also record the soil type, paddock history (e.g. zero or minimal till or regular cultivation) and the paddock’s cropping history.