To kill grub worms, use specialized chemical insecticides or natural treatments such as nematodes, neem oil and milky spore. The effects of grub worm infestation appear between late summer and early fall as irregular brown patches on the lawn that easily detach from the soil. Inspect different areas of the lawn by digging small holes to check for worms. Five worms per square root require treatment.
Treat the lawn for grub worms when they are small, between late summer and early fall. Treatment is ineffective during rain seasons and when grub worms are bigger and not feeding.
Use Dylox to kill grub worms. Merit and Mach-2 insecticides target grub worms before they lay eggs, making them more useful as a preventive measure. Natural treatments are effective at treating grub worm infestation without harming wildlife and other beneficial insects.
Milky spore takes between 7 and 21 days to kill grub worms. These bacteria quickly reproduce inside grub worms when ingested. Decomposing grub worms release milky spore into the soil, infecting any remaining worms. Apply milky spore to the soil in August, when grub worms are near the surface.
Mix neem oil with water and spray the lawn to repel grub worms and Japanese beetles.
Beneficial nematodes are microscopic roundworms that produce bacteria lethal to grub worms and other pests. Apply when the lawn is warm and moist.