Slugs

Farmer Michael Nash reports the presence of slugs in several newly sown crops in the Western district of Victoria. The most common slug species are the Reticulated Slug and the Black Keeled Slug, which both grow to about 40mm long. The April soaking rains have stimulated the adult slugs out of their summer aestivation, generally in paddocks were they have previously been a problem. Slugs damage plant seeds and seedlings, mainly feeding at night. Damage to seedlings is often in patches and may result in the death of plants. Although all seedling crops and pastures may be attacked, canola is particularly susceptible.

Slug numbers can be monitored by placing carpet squares or tiles on the soil surface and counting the number under them after a few days. Once the crop has been seeded and germination is commencing, crops should be examined at night for slug activity. It is also a good idea to continue these checks to determine the effectiveness of control methods.

There are a number of effective control measures for slugs, including chemical, cultural and biological methods. The most common control method is to apply baits, but these should be applied early in the season after good germinating rains. This is when slugs are emerging from their hiding places and actively looking for food. This means there is little alternative food to compete with the bait pellets and adults are likely to be killed before they have laid eggs. Baiting (using a suitable application method) in early autumn around crop edges may minimise the impact of slugs invading from surrounding pasture or fence lines.

Paul Horne (IPM technologies) says iron-chelate based compounds rather than traditional chemicals (eg. Mesurol) can help maintain a healthy population of beneficial species, such as carabid beetles which are veracious predators of slugs. Abundant ground cover and stubble can provide ideal moisture levels and shelter for slugs. Good hygiene, weed control and removal of refuges can reduce the problem over time. For more information on the biological control of slugs click here.

Look out for a Slug ID guide being produced by GRDC and set for release next month.