Grub worms are more than just an annoyance: These little insects can actually do serious damage to your garden, eating the lawn and causing the turf to pull up from the ground. Common animals such as moles are attracted to the worms and can come hunting, leaving holes and other messes. You can kill grub worms with Dawn soap.
Boil 4.5 litres (1 gallon) of water in a large pot. While the mixture is boiling, add 440 g (2 cups) of Dawn soap, 474 ml (2 cups) of antiseptic mouthwash and 1 tbsp of cayenne pepper. Let the mixture cool completely before pouring it into a spray bottle.
Locate the areas in your garden where you see grub worms and apply the mixture. Coat the plants, grass and trees completely to kill the grub worms.
Water your plants and garden as usual after you use the mixture -- at least once a day. This helps rinse off the excess soap from your plants, as well as any dead grub worms or debris left from the grub worms.
Pour a small amount of the mixture around the base of your plants and trees, especially those where you saw grub worms. This acts as a deterrent and stops other grub worms from climbing onto your plants, since the bugs don't like the smell.
Spot treat your plants with the mixture at least once a week to kill grub worms. Check for any signs of the bugs, including live ones on the plants. Spray the bugs with the mixture. All of the bugs should be gone within two weeks.
You might need to create a second batch of the Dawn soap mixture and apply it to your plants a second time if the infestation is severe. Some homeowners have success using less Dawn soap. You can start out by adding only 110 to 220 g (1/2 to 1 cup) and see how that works before using 440 g (2 cups).