Slugs

Slugs continue to cause significant problems across most parts of Western Victoria. Agronomist, Craig Drum (Tatyoon Rural), says slugs have been observed in large areas between Hamilton, Ararat, Colac and Warrnambool, in the Western district of Victoria. The number of slugs found in many paddocks this season has been staggering. Although most of the damage has occurred to canola, other crops including cereals have also been badly affected. Craig says growers have already baited some paddock three separate times. The predominant species being found is the grey field slug (Deroceras reticulatum), although black-keeled slugs (Milax gagates) are also present in many paddocks.

Agronomist, Natalie James (Elders), says slugs have been problematic over large areas around Ballarat, in the Western district of Victoria. Natalie estimates that about 90% of paddocks have been affected to varying levels this season. The extent of damage is largely dependant on soil type and stubble retention. Canola, wheat and some newly sown pasture paddocks have been attacked, however multiple baitings at the right time have minimised the level of feeding damage. Because emergence and plant growth have been relatively slow this season, Natalie says the period of time in which crops are susceptible to slugs has been extended. Consultant, James Christie (JSA Independent), has also experienced significant issues with slugs in canola and cereal crops around Tatyoon, in the Western district in Victoria. James says very high numbers of slugs and their eggs are presently being found across many paddocks.

Agronomist, Eoin Flett (Williams & Jackson), says slugs have caused issues around Drysdale and Portarlington, in the Central district of Victoria. A large number of paddocks have been found with slugs, with a proportion experiencing severe feeding damage. Some growers are considering re-applying slug baits in the worse affected paddocks.

District agronomist, James Fleming (I&I NSW), also reports slugs causing damage to a seedling canola crop near Coonabarabran, in the Central West Slopes and Plains district of New South Wales. James says approximately 350 acres has been severely damaged. The paddock has heavy black soils, contains a large amount of stubble and is under a no-tillage regime. These are all favourable conditions for slug survival. Both grey field slugs and the black-keeled slugs have been found within the paddock.

At this time of year there are relatively few options to control slugs. Foliar applications of insecticides should not be used. Baiting remains the most effective strategy with a number of reports suggesting the application of higher rates has been worth the added expense due to high slug numbers. Multiple baiting is likely to be needed in many instances; the effectiveness of baits being dependent on slug activity and food availability. Growers should consider the rain-fast properties and size of baits. Smaller baits will be more accessible to juveniles, which are prevalent at this time of the year. Always adhere to label directions, as slug baits can be dangerous to many animals including dogs. Iron-chelate based compounds rather than traditional chemicals will help maintain a healthy population of beneficial species, such as carabid beetles, which are important predators of slugs. This should help predator numbers build up to limit future slug numbers.

Researcher, Michael Nash (University of Melbourne), says slugs will to continue to breed if conditions remain wet. Grey field slugs can reproduce at any time of the year under suitable conditions. The black-keeled slug has a biennial lifecycle but overlapping generations have been observed this season. The brown slug (Deroceras panormitanum) and the striped field slug (Lehmannia nyctelia) are also being found in some paddocks. To help with understanding the distribution of the different species of slugs, Michael would like advisers and growers to record slug species and location, and email to manash@unimelb.edu.au. If you are unsure of the species call Michael on (03) 8344 2523 for assistance with identification.

For more information about monitoring and control options for slugs, refer to PestFacts Issue No. 1.