Crop Protection
BAITING TIMING FOR SNAILS AND SLUGS
Grain industry research has found that the timing of bait applications is critical to reduce snail numbers and protect emerging crops from slugs. Understanding when individuals of different species are active, mating and breeding, underpins the successful management of snails and slugs. With above average rainfall across large parts of the south-eastern cropping regions recorded throughout the 2022 crop season, many growers are anticipating higher than usual numbers of slugs and snails this season. SNAILS Wet autumn and winter conditions favour snail breeding. As a result, snail numbers increased in 2021. An AgNova project monitoring snail reproduction in South Australian vineyards to improve bait timing, observed garden snails mating over summer. Initial findings suggest garden snails are opportunistic breeders, therefore multiple applications of baits within a season will be required. The idea that snails hibernate over summer (aestivate) is misleading; timelapse footage shows snails moving whenever moisture is available and
feeding once individuals are hydrated. In trials, IRONMAX Pro® was applied to a paddock in the southern Yorke Peninsula after 40 mm of rain in January. Over 90 per cent of the Italian snails feeding on it were killed. In comparison, conical snails in the same paddock did not feed on the baits – they were not in an active state. Growers need to monitor 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 and timely follow-up baiting prior to harvest, it 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 nine 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 three to four 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 (see graph below). Proactive growers applied bait after seeding to protect seed and seedlings, but where branbased 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 to 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.
Slug population dynamics in southwestern Victoria, 2019-2021.
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