High stubble loads for shelter, rain events and cool weather has led to an increase in slug numbers across the Wimmera and Mallee.
The adoption of minimum tillage and stubble retention also provides the ideal habitat for slugs, with moisture the key for population increases.
The challenging part of slug management is identifying and monitoring activity. Populations of slugs are hard to monitor and identify due to their nocturnal nature, making dawn and dusk the times when crop inspections should take place.
Refuge traps – such as terracotta tiles, flowerpot bases or even carpet squares – are useful for assessing slug populations.
Place refuges in a ‘W’ shape in suspect paddocks and check them in the morning. Monitoring slugs this way will not provide an absolute assessment of slug density, but will provide an indication.
Slugs attack emerging crops, especially canola, which are more susceptible to damage. While seedlings are most vulnerable, slugs will eat all parts of the crop.
In a 2013 GRDC report, titled The Current and Potential Costs of Invertebrate Pests in Grain Crops, an estimated $25.9 million in lost production was reported due to slug damage.
Slugs will take the opportunity to breed and feed whenever there is sufficient moisture, usually between mid-autumn and late spring.
When conditions are too dry, they will find crevices in the soil to shelter.
Once laid, eggs will hatch within three to six weeks, depending on conditions.
Monitoring numbers and conditions is advised if populations are as low as one grey field slug causing significant damage, especially in canola crops.
An integrated pest management approach – chemical, cultural, and biological – needs to be used for slugs as no single control method is completely effective.
For more information on slug management, including baiting and other control measures, read the GRDC slug identification and management factsheet.