Monitoring of slug populations in western Victoria showed a marked increase in slugs in spring, especially striped field slugs that are still active. This is similar to what was recorded in 2013.
Extended wet spring conditions have allowed breeding to continue. It is these juvenile and adult slugs that survive over hot dry summers to become a threat to establishing crops the following season.
Grey field slug activity and egg laying are associated with 25 per cent soil moisture. Probes have shown 0 to 10cm soil moisture is above 25 per cent where slugs are still active in February 2017.
A Grains Research and Development Corporation project (DAS0160) aims to understand and validate “slug risk” from year to year. Slugs are thought to become active after 75-80mm of rain at the autumn break, which will also be tested.
Southern Farming Systems (SFS) is collaborating with the South Australian Research and Development Institute to better understand slug biology and manipulate stubble conditions to lessen slug population build up.
Previous research has shown the value of cultivation and removal of stubble in reducing slug populations. Cultivation improved seedling establishment even when it was only one week prior to sowing. Where no cultivation took place, control was solely reliant on more expensive bait products such as Metarex or multiple applications of bran-based baits such as Meta.
Basic rules for successful crop establishment are: quick establishment sowing into warm soil using larger seed; cultivation prior to sowing; rolling directly after sowing then bait to protect seedlings; follow up monitoring to ensure baits are present; and consider reapplying bait to problem areas or high pressure years such as expected this year.
Where canola is being established into no-till situations in 2017, growers should consider more expensive bait products or multiple applications.
Michael Nash is a senior researcher in the entomology unit at the South Australian Research and Development Institute.