Mollusc mitigation – what risks do snails and slugs pose?

“If you have to clean snails out at harvest, you have not done your job properly at the start of the season.” Control of snails and slugs requires timely application of baits, based on understanding when and where the greatest threats exist, the makers of Metarex say.

Snails and slugs are adapted to the variable Australian climate “lottery”, with numbers fluctuating between seasons. Recent GRDC research highlighted the interaction between climatic conditions and snail and slug numbers, with available moisture being the main factor. Good growing seasons equal larger snail and slug populations, hence greater risk to crops. Wet conditions continuing into 2021 across most of eastern and southern Australia have been ideal for snail and slug breeding.

Following two dry seasons, small numbers of snails were observed in the autumn of 2020 across most vineyards, so bait was not applied. By spring, large numbers of snails were observed, with baiting required to protect new growth. Applications of an attractive product, Metarex Inov, resulted in excellent control. Italian snails from vineyards in south-east South Australia on average were 5-7 millimetres larger than previous years, indicating 2020 was an excellent year for numbers to build up. Larger adults produce more eggs.

Autumn applications of Metarex Inov, before eggs are laid, will provide the best reduction of snails. A recent trial on garden snails in citrus orchards indicated a doubling of efficacy when Metarex Inov was applied in March compared to winter. Similar results have been observed across broadacre crops. This season, in early March, a 100 per cent kill was achieved on Italian round snails using Metarex Inov under ideal conditions: dewy mornings followed by dry, warm days with snails being active after mating.

Last year also favoured the build-up of slug populations, with breeding continuing all year in some areas due to good soil moisture (>30pc v/v). Monitoring from southwest Victoria (Fig. 1) supports observations that there are massive populations of grey field slugs awaiting canola to emerge. Application of Metarex Inov at sowing, after rolling, will protect seed and seedlings. Follow-up monitoring is required to ensure bait remains, hence continuing to protect seedlings. Also, follow-up applications of Metarex Inov may be required this year, with the confidence that juvenile slugs will be controlled as was observed last spring in poppies.

Proactive baiting using an attractive, palatable, persistent product that delivers a lethal dose, integrated with cultural practices and conservation of natural enemies, will protect crops and eliminate contamination of produce.