Furadan (trade name for carbofuran) is used as a contact and systemic poison. Furadan comes in small granules coloured purple or red. It kills earthworms, nematodes, ants, and other animals in the soil by contact. It is also absorbed by roots into the plant, and kills sap-sucking insects such as aphids and mealy bugs; probably leaf-eating caterpillars too.
I have applied furadan to soil to control ants and mealybugs; the ants by contact and the mealybugs by systemic action. The ants were eliminated but came back after one week. Mealybugs were back after two weeks. Hence the poison wears off fairly quickly. On plants growing on the ground, there is a danger of furadan being over-applied by frequent re-application. For plants in pots and containers the use of furadan is more ‘containable’. A light sprinkling of granules on the surface of the soil in the container is enough to rid the soil of earthworms and nematodes. Earthworms are especially lethal in containers used to nurse cuttings or young seedlings, and nematodes destroy the roots and tubers of dahlias. A treated container should be kept out of contact with the ground, so that once treated, the soil it contains will remain free of worms for a very long time. Against ants and sap-sucking insects associated with ants, repeated application may be necessary but in a pot, the furadan will be contained and not get into the ground.
I prefer gardening with soil that is sterile to begin with. Burnt soil (available in bags in Kuala Lumpur at RM1.50 per 3kg bag) is soil that has been baked over a wood fire for about a week. This can be used alone or mixed with biochar/ horticarbon (granulated charcoal, available at RM 10 per 5kg bag). I have no worms in my pots unless I get careless and allow my pots to come into contact with the ground. Worms can enter via the drainage holes at the bottom of the pots.
I do not do any mulching or composting. I find that mulch and compost promote the multiplication of snails, earthworms and termites. In the humid tropics mulch and compost also get soggy as they decompose, impede aeration of the soil, and compete with roots for oxygen. Visitors to the rooftop ‘Secret Garden of 1 Utama’ may have noticed that it is free of mulch and compost. All the garden trimmings are stuffed into big bags and sent down by lift for disposal elsewhere.
The role of earthworms in the humid tropics needs more investigation. Many years ago I assigned a young scientist to study earthworms in the Malaysia forests and guess what? He could not find any! It seems that earthworms are rare in tropical rain forests. I suspect the earthworms in our farms and gardens are of foreign origin. The breakdown of litter in the forests is done by insects, especially termites, not by worms.