Monitor for slugs now to prepare for next season
Growers and consultants in the south coastal areas of WA are urged to monitor paddocks for slugs this spring. Assessing slug numbers and distribution in paddocks at this time of year will prepare growers for slug management next year.
The two main slug species present in WA are reticulated slugs and black-keeled slugs. For more information on diagnosing these slugs visit DPIRD’s identification and control of pest slugs and snails for broadacre crops in WA page.
Tips for monitoring for slugs
Growers are advised to focus on paddocks with a history of slug activity, which were not baited earlier in the season. Additionally, it’s important to look in adjacent paddocks, especially those that have heavier soil.
Reticulated slugs aestivate over summer under surface refuges such as rocks, in dead stalks and in soil cracks. Conversely, black-keeled slugs will actively burrow underground, meaning that they can be found in sandier soils in high rainfall areas. Both species of slugs survive hot summers by seeking moist refuges and will persist in paddocks where burning has occurred.
In spring, growers should survey paddocks to determine the areas where slugs are most likely to pose a risk at crop establishment. This will help you strategically apply baits in the following year. The best time to find slugs actively moving is nine hours after sunset, when temperatures are 7°C or above and humidity surpasses 90%. Slugs can be found during the day by looking under stubble and rocks.
During spring, if you find small slugs in the crop canopy on a wet day feeding on the flag leaf, this is a good indicator slugs are likely to cause problems next autumn.
You can also monitor for slugs by placing refuges (such as carpet mat, wet hessian sacks, tiles or plastic drums half full of water) out in paddocks and checking them the following morning. As slugs often have a patchy distribution, it is important to use multiple refuges. Fifty monitoring refuges are recommended for each 40 hectares paddock size due to their variability in Australian conditions.
Another strategy is laying bait lines before sowing in paddocks across patches identified by spring monitoring. Inspect these areas for any dead slugs the following day.
Slug management
Spring baiting has not been successful in reducing next seasons slug numbers, however further research is investigating options to reduce slug populations in the spring.
Monitoring during spring provides an understanding of the success of any management practices in autumn 2023. If you do detect slugs in your maturing crops, take note of the paddock, as this is where they will be in 2024. This will allow the ordering of baits, selection of crops and the implementation of cultural controls prior to sowing crops next year. By identifying your slug risk for next season’s establishing crops, you can plan to bait next autumn after sowing to protect emerging crops.
Best practice management of slugs requires an integrated approach.
GRDC is providing a hands-on slug management workshop on Monday 4 September at Qualeup. It is being delivered by Dr Michael Nash. For more information on this workshop, visit the event webpage.
Further information
To read about previous slug and snail activity this season, refer to the 2023 PestFacts WA articles:
- Issue 4 Growers may need to reapply baits for slugs and snails
- Issue 2 Slugs and snails have started to lay eggs
- Issue 1 Now is the time to bait snails.
For more information on slugs visit:
- DPIRD’s Identification and control of pest slugs and snails for broadacre crops in WA page
- GRDC’s Slug control fact sheet: Successful crop protection from slugs
- GRDC’s Slugs in crop: The back pocket guide.
For more information contact Research scientist Svetlana Micic in Albany on +61 (0)8 9892 8591.
Article authors: Svetlana Micic (DPIRD Albany) and Dr Michael Nash (Consultant).