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Vine Weevils; Soil Sterilisation with Lime Sulphur

One persistent nemesis that can disrupt the beauty of our gardens is the vine weevil. These notorious pests can wreak havoc on a variety of plants, particularly those in containers and pots. Fear not, fellow gardeners! In this blog post, we will delve into the world of vine weevils and explore an effective control method: soil sterilisation with diluted Lime Sulphur.

Understanding Vine Weevils

Vine weevils, also known as Otiorhynchus sulcatus, are small beetles that pose a significant threat to a wide range of ornamental plants, fruit trees, and vegetables. They are especially problematic during their larval stage, as the grubs feed on the roots of plants, causing significant damage and even death in severe cases. Adult vine weevils, characterised by their dark brown or black colour and distinctive “elephant snout” appearance, feed on leaves, leaving unsightly notches.

Soil Sterilisation with Lime Sulphur

One effective method to combat vine weevils is soil sterilisation using a diluted solution of Lime Sulphur. Lime Sulphur is a simple sterilant created by reacting calcium salts with sulphur. Lime Sulphur has powerful fungicidal and bactericidal properties, however, it also exhibits control effects against vine weevil eggs, larvae, and adults when applied to infested soil. Here’s how you can implement this technique:

Preparation

Clear away all debris and thoroughly clean the containers to eliminate any potential hiding places for vine weevils.

Dilute Lime Sulphur Solution

Follow the instructions provided on the Lime Sulphur product packaging for dilution ratios. Generally, a 1:40 ratio of Lime Sulphur to water is recommended (25mL of Lime Sulphur per litre of tap water). It is essential that you follow the proper safety precautions listed on the label when using Lime Sulphur, including wearing protective gloves, goggles, and a TYPE B filter mask. As part of its action, Lime Sulphur releases hydrogen sulphide gas which smells of rotten eggs and is hazardous to humans. So only use in well ventilated areas. After a few hours, diluted Lime Sulphur will be fully reacted and is no longer hazardous. It actually converts into plant-available nutrients (calcium and sulphur). As Lime Sulphur has a non-residual action, and is composed of simple chemicals, it can be used in organic growing.

Lime Sulphur miticide, insecticide, organic vine weevil

Soil Treatment

Pour the diluted Lime Sulphur solution slowly and evenly over the infested soil, making sure to thoroughly wet the entire root zone. The solution works by releasing hydrogen sulphide gas which sterilising the soil, killing any vine weevil eggs, larvae, or adults present. It also helps in preventing fungal and bacterial diseases that can further weaken the plants. 

Repeat treatments and future care

If your plants continue to suffer from Vine Weevil after two treatments, fortnights apart, you can increase the dose rate to 50 mL of Lime Sulphur / litre of tap water, however, the compost must be wet already, and sensitive plant roots may also be harmed by higher doses.

Biological Control: After treatment with Lime Sulphur, consider incorporating a biological control methods like beneficial nematodes to enhance long-term vine weevil management. This will work well because the Lime Sulphur is non-residual and will not harm the nematodes. This is not the case if you use a residual insecticide to control the vine weevils.

Regular Inspections: Routinely check your plants for signs of vine weevil damage, such as notched leaves or wilting plants. Early detection can help prevent severe infestations.

Physical Barriers: Implement physical barriers, like fine mesh or horticultural fleece, to protect young vulnerable plants from adult vine weevils.

Plant Selection: Choose plants that are less susceptible to vine weevil attacks. Research resistant varieties and diversify your garden to minimise the risk.

Vine weevils can be a persistent problem in our gardens, but with the right strategies, we can regain control and protect our beloved plants. Soil sterilisation with diluted Lime Sulphur offers an effective and organic solution for eradicating vine weevil infestations. By following the steps outlined in this blog post and combining them with other preventive measures, you can start to win the battle. Happy gardening!

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