Slugs

Slug populations have increased substantially over the last two seasons due to high summer moisture. Growers in high rainfall areas are advised to identify and monitor slug populations to avoid unexpected seedling damage. In a typical year, slugs are stimulated out of their summer aestivation following autumn rains and will generally be problematic in paddocks where they have previously been found. Heavier soils are preferred, typically heavy red loams, gravelly loams and grey clays.

Agronomist, Bruce Larcombe (IK Caldwell), has reported high numbers of slugs in various paddocks north of Shepparton, in the Northern Country district of Victoria. As is typical, the distribution of slugs across paddocks is quite patchy and Bruce says slugs have been found in paddocks that have not previously been known to have issues. There is also evidence of slugs being found from many paddocks in the southern part of the Riverina district of New South Wales and the North East district of Victoria. Slugs are also active across the Western district of Victoria. Consultant, Steve Dickson (CropPlus Agronomy), has reported slug activity in paddocks around Inverleigh and Bannockburn. Steve says slugs are mostly being observed in paddocks where they were previously a problem, and are easily found in stubble and under weeds.

Because slugs are more active at night, it is difficult to estimate numbers accurately without monitoring. Using terracotta tiles, or another type of refuge ‘trap’ such as carpet squares is the best way to assess numbers. Traps should be placed on the soil surface when it is visibly wet, and then checked after a few days for the presence of slugs underneath. A few pieces of slug bait under each trap will help to attract slugs if they are present.

The most common control method for slugs is to apply baits, which, under normal conditions should be applied early in the season after good germinating rains to coincide with slug emergence. Baiting efficacy can be reduced when there are higher slug populations, an increased availability of refuges, and higher amounts of plant material. When baiting, it is important to consider the number of baits that are spread per m², and how this relates to the numbers of slugs present. Economic thresholds for slugs vary depending on the species.