How to exterminate earthworms
Earthworms benefit the garden by enriching and aerating the soil. However, in some parts of the garden like the lawn, the worms deposit digested earth worm casts. These casts look unsightly in a well-manicured lawn. Earthworm casts can blunt the blades of a lawnmower.
Weeds grow on earthworm casts and pose a hazard for other plants in the garden.
Fertilise the lawn regularly. Fertiliser has properties to control earthworms. Fertiliser applied to a well-irrigated lawn will control earthworms effectively.
Apply pesticide to the lawn. Pesticide may kill earthworms rather than prevent earthworm infestation. If the lawn suffers excess damage by earthworms, pesticide will effectively exterminate them. Chemical vermifuges like potassium permanganate or formalin will not kill earthworms but effectively bring them out so that they can be swept away.
Water the lawn sparingly. Earthworms thrive in moist soil. They breathe through their skin and constantly require moisture. If the soil is dry, they bury themselves deeper into the soil to find moisture and do not come to the surface.
Mix dry mustard and water and apply to the soil in the evening. The pungent smell of the mustard repels earthworms. Unlike chemical pesticides, mustard will not kill earthworms. Mustard is also a safe vermifuge, unlike chemical pesticides or chemical vermifuges.
Install a bird feeder in the lawn. Birds not only feed on the nuts and seeds placed in the feeder but also on earthworms. When birds frequent the lawn the population of earthworms will dwindle.