`Baiting for slugs and snails.

Article by AgNova

The timing of bait applications is critical to reduce snail numbers and protect emerging crops from slugs, grains industry research has found. Understanding when individuals of different species are active, mating and breeding underpins successful management of snails and slugs.  

Above average rainfall across large parts of the south eastern cropping regions has been recorded leading up to the 2022 crop season where slugs and snails traditionally cause issues. The expectation is greater threats this season.

Snails

Wet autumn and winter conditions favour snail breeding, hence snail numbers increased in 2021. Garden snails have been observed mating over the summer in SA, as part of an AgNova/Nutrien WA project monitoring their reproduction in vineyards to improve bait timing. Initial findings suggest garden snails are opportunistic breeders, hence multiple applications of baits within a season will be required.

Italian snails were feeding on IRONMAX Pro® applied after 40 mm of rain in January on the southern Yorke Peninsula, with over 90% killed. In comparison, conical snails in the same paddock did not feed on the baits – they were not in an active state. The idea snails hibernate over summer (aestivate) is misleading; time-lapse footage shows snails moving whenever moisture is available and feeding once individuals are hydrated.

Growers need to monitor the snail activity and apply bait accordingly. In 2022, this may mean baiting from late February onwards, when round snails will be actively feeding and again later in April, when conical snails will be actively feeding after mating. With the introduction of the iron phosphate product, IRONMAX Pro, timely follow-up baiting prior to harvest is possible to eliminate snails due to the nil withholding period. This newly registered product has a great fit in intensive pasture systems. 

Slugs

Slug activity and breeding has benefited from La Niña, with large numbers expected to carry over into 2022. Taking longer to grow than grey field slugs, black keeled slug numbers are expected to be greater again in 2022. In 2021, black keeled slugs were observed in April, but a large number also emerged mid-May, when the “black wave of doom” is usually observed. This is consistent with overseas research: slugs emerge from the ground over an extended period, up to 9 months for grey field slug populations. What is observed on the soil surface is only the active proportion of the slug population at any one point in time; the total number is often much greater. This highlights the need to not be complacent: use long lasting baits for sustained control where monitoring of establishing crops every 3-4 days is not possible. 

In areas that had a long cool spring in 2021, numbers of grey field slugs built up as suggested by spring monitoring (Fig. 1). Proactive growers applied bait after seeding to protect seed and seedlings, but where bran-based pellets were used, had to reapply after substantial rainfall. Those using an all-weather product, such as Metarex Inov®, were controlling slugs with this single application after 50-80 mm of rain.

Long term monitoring is vital to understand when snails and slugs are ready to take baits, so management can be proactive to achieve the best results.  

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