PestFacts 28 July 2023
Slug activity across the state
Projections from last spring's conditions (see PestFacts October 2022) of high slug populations over-summering have happened, even in areas of South Australia. While it was very dry over autumn, recent rains are contributing to high numbers of slugs.
Recent slug monitoring and reports
At Jamestown, following 23 mm of rain in early June, ongoing monitoring revealed black keeled slugs under refuge mats even after baiting paddocks with 5 kg per hectare of short-lasting bran-based baits. Three weeks later, there were on average three slugs per refuge and four adult black keeled slugs per refuge by July.
Reports are coming in thick and fast from areas like lower Eyre Peninsula and the South East where slugs are traditionally a problem. However, there are also reports that slugs have expanded into new areas, such as further north in the hills near Ungarra on the Eyre Peninsula, where slug feeding has damaged canola.
Slugs have been traditionally a problem at Wirrabara in the Upper North but growers are managing to stay on top of black keeled slugs with only minor crop losses observed.
Damage caused by slugs has also been reported in wheat grown in the southern region of Yorke Peninsula around Corny Point. Several paddocks in that region have also been baited, particularly to control black keeled slugs damaging canola, wheat, and lentils.
Long-term monitoring at Finniss has also showed black keeled and grey field slugs are active on the surface damaging wheat, and some protection has been provided by short lasting bran-based baits.
Slugs have been widespread this season in areas south of Naracoorte, such as Bool Lagoon and Millicent, with four or five applications of bait on some paddocks, particularly in crops following faba beans. Very high numbers of black keeled slugs are continuing to emerge from the ground. Many growers in the Millicent area have lost canola where bait was not reapplied within a week after previous bait was eaten one or two nights after application. Many wheat crops, particularly in crops following a canola crop, have also been baited.
Growers have reported that waterlogging in the South East has drowned many slugs.
In south-western Victoria, long-term monitoring in susceptible crops found slugs persisted even after growers had applied baits. Slugs are particularly persistent where trash rows are present in the paddock. Given last season's optimal breeding conditions, slug numbers are very high and label rates of molluscicide baits have not been enough to supress emerging slugs. Multiple bait applications at label rates have been needed to protect canola, and in some cases wheat, from slugs.
Further north in areas of western Victoria , some lentil crops have needed bait applied. This is the first season regular reports of slugs damaging lentils has been recorded.
This season has seen anywhere from $142 to $200 a hectare spent on slug and snail bait in an effort to protect establishing crops in areas where slugs are traditionally a problem.
Current slug management observations
Cultural practices that have shown to be the best strategy for successfully establishing canola crops this season have been:
- paddock burning followed by cultivation
- early baiting with short-lasting products to knock down numbers (while conditions are warm)
- reapplying long-lasting quality products as a follow-up to protect crops during establishment.
Proactive growers applied cultural practices early in the season, baited and successfully established new crops. A similar trend was seen with snail control this season.
The major issue has been when canola has followed faba bean crops, especially where trash rows exist. There have also been problems with bait application, particularly using small baits applied on windy days and a full spread of bait has not been applied to the paddock.
After the wet spring of 2022, monitoring of slug populations in the spring is the best strategy to determine next season’s threat, ensuring bait can be ordered early, or alternative crops sown in high-risk areas.
More information
- Snail and slug baiting guidelines ()
- Slug control fact sheet
- Slugs In Crops: The Back Pocket Guide
- Slug control across southern Australia
- Slugs – what can we learn from 2022
- Latest GRDC slug control tactics now available for growers
- Slug numbers increase across south-eastern Australia thanks to triple La Niña
- GCTV17: Slug bait timing - monitoring techniques
The latest information for growers and advisors on the activity and management of pests in all broadacre crops during the winter growing season.
