Black-keeled slugs are usually black with a prominent ridge down their back, and can burrow to a depth of 200 millimetres or more.
To minimise the impact of slug damage to crops, grain growers in Western Australia’s high rainfall areas are encouraged to monitor paddocks and to use sufficient baiting rates to control the pests.
Department of Agriculture and Food (DAFWA) entomologist Svetlana Micic said black-keeled slugs were at higher-than usual levels and damaging emerging crops in areas including Williams, Boyup Brook and Frankland.
“A wet summer followed by a wet start to the cropping season has provided ideal conditions for slugs which can be a particular problem in canola or pulse paddocks with high levels of stubble retention or rock piles which provided protective sites over summer,” she said.
Ms Micic, who conducts slug research supported by the Grains Research and Development Corporation (GRDC), said black-keeled slugs were usually black with a prominent ridge down the back, and could burrow to a depth of 200 millimetres or more.
“Slugs will attack all plant parts but seedlings are the most vulnerable crop stage and can suffer major economic damage,” she said.
“They can be under-estimated as pests because they are nocturnal and shelter during dry conditions, and therefore are not generally visible during the day.”
Ms Micic said one monitoring method was to create 300mm by 300mm ‘surface refuges’ in paddocks, made of materials such as carpet or terracotta paving tiles, which could give an indication of slug activity and numbers present.
“Aim for about 10 refuges per 10 hectares and check them early in the morning as slugs seek shelter in the soil as it gets warmer. The suggested threshold for baiting is one to two slugs per square metre.
“When monitoring is not practical from a time or resource perspective, an alternative option is to put out lines of bait to gauge populations, especially in areas where slugs occurred previously.”
Ms Micic said baiting was the only chemical control option and should be applied at adequate rates where required.
“During winter, continue to monitor for any plant damage - repeated baiting may be required during crop establishment,” she said.
Ms Micic said other management strategies included controlling weeds in summer which would decrease available food sources and increase the effectiveness of baits by removing food competition.
A new project is commencing, funded by the GRDC and led by DAFWA in WA, which aims to expand ecological and biological knowledge of specific snail and slug species, including black-keeled slugs, to provide growers with regionally specific information to allow them to effectively and economically manage these pests.
In addition to this and other ongoing research projects, shorter-term, regionally-based GRDC Regional Cropping Solutions Network (RCSN) slug projects are due to commence in coming months.
Information on identifying and managing black-keeled slugs is available in the GRDC Slug Control Fact Sheet; the GRDC Slugging Slugs Hot Topic; and Diagnosing slugs in crops information on the DAFWA website.
Svetlana Micic, DAFWA
08 9892 8591
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code