Ploughing gets rid of slugs by burying their eggs, disrupting their habitat, and destroying their shelters.
Reducing slug attacks with ploughing
Whether in a vegetable garden or on a larger field, slugs are notorious plant pests. Farmers can naturally combat slug populations with ploughing. The plough helps to disrupt slugs by delaying their attacks and reducing the number of eggs that survive through the winter. This practice complements chemical slug control methods
Favourable conditions for slug development
Slugs are widespread pests, with two main species: the grey slug (Deroceras reticulatum) and the black slug (Arion hortensis). In France, 80% of slug attacks are caused by grey slugs. Several factors influence slug development:
grey slug
black slug
Weather conditions
- Slugs are made up of 80% water, so they need constant moisture to live and move.
- Warm, wet weather is ideal for their population growth.
- Mild winters with little or no frost also promote slug proliferation, as they tend to shelter in the top 15 cm of soil and reappear in the spring when crops begin to sprout.
Availability of shelters
- Slugs find refuge in clayey and clay-loam soils with lots of clods.
- They can also nest in residues and plant cover.
- Slugs lay their eggs within the top 10 cm of soil, making them difficult to spot.
- Plant debris provides a suitable habitat for egg-laying, offering moisture and shelter from potential predators.
Food availability
- Slugs travel an average of 3 metres a day. This is why their food must be near their habitat.
- Slugs are omnivores and can consume up to 50% of their body weight in food.
- They prefer young shoots and leaves, particularly from crops such as sunflowers, rapeseed, maize, potatoes, cereals and fodder crops.
Development cycle of slugs with sensitive stages for main crops
- Egg laying of slugs
- Young grey slugs on a corn plant
- Garden slugs with a well-visible yellow-orange foot
- Iberian slugs with a well-visible pneumostome (breathing hole)
- Grey slugs during copulation (hermaphrodites)
- Grey slug laying its eggs
Despite their limited mobility, slugs can cause significant damage due to their rapid reproduction. Like snails, slugs are hermaphrodites, meaning they can mate with any other adult slug. Slugs can lay up to 100 eggs, often 3 times a year, from August to October, which hatch in the spring.
Consequences of slug attacks on crops
Yield loss
Slugs feed on both leaves and seeds, hindering plant growth. If an attack occurs during germination, it can lead to partial or total yield loss.
Disease development
Slug attacks on growing plants can cause holes in the leaves, providing entry points for fungal and bacterial infections.
Damping-off is caused by a fungus (Fusarium is often behind attacks on cereals) that lives in the soil and can infect all types of crops. It attacks young plants and causes them to rot.
Take-all disease affects wheat and other straw cereal crops. The fungus causes the plant to dry out and rot. This disease is more likely to develop when the previous crop was a cereal and when straw has been added to the field.
Like take-all, eyespot disease also targets straw cereal crops. The lesions it creates on the plant can lead to patchy lodging in the field, which makes harvesting more difficult. On top of that, the ears can be hit too, leading to significant yield losses.
Ploughing to combat mycotoxins in crops
Fusarium species produce mycotoxins like deoxynivalenol (DON), zearaleone (ZEA) and the toxins T-2 and HT-2. In France, DON is the toxin most commonly found in cereals such as wheat, oats and triticale. These molecules are extremely stable and can persist through food processing, meaning we can find them throughout the food chain. At high levels, these toxins pose risks to animals and humans.
Precautionary measures are essential, especially since it's nearly impossible to completely eliminate the threat posed by mycotoxins (such as through early sowing, irrigation, residue management, controlling crop pests like slugs and insects, etc.).
Ploughing helps reduce the spread of these toxins by burying infected plant residues. For example, burying cereal straw and unharvested maize stalks reduces the amount of inoculum. Without this practice, Fusarium can persist on the surface and contaminate subsequent cereal crops.
Agronomic measures to control slugs
The intercropping period is the most favourable time for gastropod proliferation. Farmers should use multiple soil tillage passes to disrupt slug movement and reproduction, exposing their eggs to the drying effects of the sun.
Estimation of slug activity
Factors inhibiting activity before sowing | Factors favoring activity before sowing | ||
|---|---|---|---|
| Winter with frost |
| Mild Winter |
|
| Low degree of soil cover |
| High degree af soil cover |
|
| High tillage intensity |
| Low tillage intensity |
|
| 🟡🟢 |
| 🟡🔴 |
|
Factors inhibiting activity after sowing | Factors favoring activity after sowing | ||
|---|---|---|---|
| Crop not very sensitive and/or growing quickly |
| Susceptible crop, poorly developed |
|
| Dry weather☀️ | Wet weather🌧️ | ||
| 🟢 |
| 🔴 |
|
Ploughing to reduce slug attacks
The plough destroys the slugs' habitat (biotope) and buries plant residues on the surface, making it harder for them to proliferate. When the soil is ploughed, the slugs and their eggs are exposed to the surface, where they dry out and are deprived of food.
Ploughing just before sowing
However, the timing of ploughing needs to be carefully chosen. Slugs that get buried after the plough has passed can survive deeper in the soil by feeding on decomposing plant residues. That’s why ploughing should be done just before sowing, so the slugs don’t have time to come back to the surface when the crop is germinating. Depending on the type and moisture of the soil, it can take slugs anywhere from 10 to 45 days to return to the surface.
Best effectiveness in loamy soils
This method works particularly well in loamy soils, where it creates a fine, dry, and low-moisture environment, which is unfriendly for slugs. In calcareous and clay-loam soils, however, ploughing may actually increase slug populations, as it creates shelter.
Rolling after sowing
It is also advisable to combine ploughing with rolling right after seeding to flatten clods and pore-filled soil, trapping slugs who cannot burrow into the soil.
In direct seeding, rolling is even more critical, as it prevents seeds from being exposed to slugs in open furrows.
The furrows need to be properly closed to reduce seed exposure. Otherwise, slugs will slip into those open furrows and feed on a large number of seeds, which can have serious consequences for crop yield. However, rolling is not recommended on silty soils that are prone to crusting.
Frequent tillage
In areas with regular slug infestations, tillage can significantly disrupt the slug biotope.
Stubble ploughing creates a fine, dry, residue-free soil surface, damaging slugs and exposing eggs to sunlight, which accelerates their desiccation. A minimum of three tillage passes is recommended to reduce slug risks.
Adjusting crop rotation to include less appetising plants
To prevent slugs from multiplying and establishing themselves, it’s essential to consider crop rotation. Switching between crops that slugs prefer (like wheat, rapeseed, and barley) with crops that are less appealing (like phacelia, mustard, and vetch) can help manage slug populations.
However, cover crops often create favourable habitats for slugs, as they maintain soil moisture and shelter.
Chemical treatments can maximise the effectiveness of agronomic practices. Slug pellets should be applied before crop germination, ideally at temperatures above 5°C, with no rain in sight and preferably in the evening, as slugs are most active at night. Spreading around plants in these conditions will be all the more effective.
In organic farming, iron phosphate-based products can be used up to 15 days after emergence to control slugs.
Natural predators such as ground beetles, nematodes, hedgehogs, toads, moles, and birds can help control slug populations. Preserving these beneficial species can enhance biological slug control and minimise crop damage.
Best practices to limit slug infestation risks
- Plough the soil just before sowing to destroy their habitat
- Roll the plot after sowing to prevent slug re-emergence
- Increase stubble ploughing to create a dry, fine surface
- Include less appetising crops in rotations to limit slug proliferation
FAQ: Agronomic Levers for Slug Control
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Tillage aims to:
- Eliminate slug food.
- Refine the soil to reduce refuges and soil moisture.
- Hinder slug movement.
- Expose slugs and their eggs to high temperatures and low humidity.
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During fallow periods, the following methods can be used:
- Shredding of residues.
- Chemical destruction of regrowth.
- Early stubble cultivation.
- Planting unpalatable plant cover.
- Repeated tool passes, including plowing just before sowing.
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When sowing, avoid direct sowing if there is a risk of slug damage. Ensure:
- A well-prepared seedbed with fine soil and well-closed to prevent slug movement.
- Seeds are sown at a regular depth, avoiding seeds on the surface.
- Higher sowing density if there is a high risk of slug damage.
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Repeated tool passes hinder slug activity and multiplication by disrupting their habitat and movement.
Sources:
- https://www.arvalis.fr/sites/default/files/imported_files/414_3682949301957769189.pdf
- https://www.arvalis.fr/infos-techniques/controler-les-limaces-en-associant-leviers-agronomiques-et-lutte-chimique
- https://www.bayer-agri.fr/cultures/limaces-a-chaque-culture-sa-propre-vulnerabilite_1047