The changing face of slug control: Growers urged to consider alternatives
With the final date for sale and distribution of metaldehyde slug pellets coming at the end of next month (June 30, 2019), and the use-up date a year later, growers are being urged to consider alternative chemical and non-chemical control methods to tackle slugs.
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Marianne Curtis
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With the final date for sale and distribution of metaldehyde slug pellets coming at the end of next month (June 30, 2019), and the use-up date a year later, growers are being urged to consider alternative chemical and non-chemical control methods to tackle slugs.
While metaldehyde accounted for 70 per cent of the slug pellet market for crops harvested in 2018 and ferric phosphate, 30 per cent, Certis arable product manager Neil Beadle says a large number of growers will begin to switch to the latter this autumn.
“Many distributors and growers will not want to carry stocks they are not able to sell or use. Eighty per cent of product is used from autumn onwards and only a small amount in spring. It will be difficult for growers to use in the first six months of next year and there is the cost of disposal if it is not used. A lot of people will start to use ferric phosphate.”
Certis has worked with the manufacturer of its SluxxHP ferric phosphate slug pellet to maximise palatability. Durum wheat flour is used for consistency and company trials have shown the pellet to have excellent anti-mould properties compared with an alternative ferric phosphate product, says technical manager Laurence Power. “Slugs will reject mouldy pellets.”
The product also contains a stabiliser which company trials on oilseed rape show keeps ferric phosphate in the pellet for longer than an alternative product, particularly in an irrigated programme, according to Mr Beadle.
Once a ferric phosphate pellet is eaten, feeding quickly stops and slugs go underground, dying within 1-2 days, says Mr Power. Unlike metaldehyde, dead slugs are not seen on the surface.
The product has no buffer zone restrictions.
Live information
Growers can get live slug pressure information by post code, input trapping data and view information about weather conditions via the new SlugWatch App which can be downloaded from the Certis website, says Mr Beadle.
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Behavioural clues to help tackle slugs
Understanding slug behaviour can help growers better target control measures, explains Newcastle University senior lecturer Dr Gordon Port. “Slugs spend most of their time below ground or hiding in vegetation. They are active at night when they feed, then rest, then feed again. Winter nights are long, so they get through many cycles of feeding and resting. There are fewer feeding opportunities in summer.”
In heavily cultivated vegetable crops they tend to be found 1-2 metres into the crop, moving from field margins whereas in arable crops which are or are following oilseed rape, for example, they tend to be found throughout but not evenly distributed, says Dr Port. “Farmers will know about patches of land they have that are very wet – it is probably the soil conditions that suit slugs rather than the crop.”
Dr Port says that while natural predators such as ground beetles may have some effect, they cannot completely solve the problem. Nematodes have been used to control slugs in some horticultural crops and gardens but are too expensive for broadacre crops, he says.
“Cultivation is good at messing up the lives of slugs – anything that interferes with the integrity of the soil. Discing has some impact and deep ploughing – this does need to be balanced against cost and risk of soil erosion but anything you can do to disturb soil does reduce slug numbers,” says Dr Port.
Rolling can also help, he adds, with some farmers choosing to roll at night when slugs are on the surface.
Before turning to chemical control, growers and agronomists should ideally monitor slug levels by trapping. For example, the threshold for wheat is four slugs/trap overnight. Timing of slug pellet application is important, says Dr Port. “Do not apply at a time when they are not active or long before the crop is at risk. After a long, persistent spell of dry weather there is not a big risk of a slug problem. Slugs are more active at above 5degC and the soil surface has to be moist.”
While there is little to choose between metaldehyde and ferric phosphate in efficacy terms, bait formulations vary, with some more attractive to slugs than others, says Dr Port.
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