Grass Grubs and how to identify if you have them! - Lawn Rite Lawn Mowing

Grass Grubs (Costelytra zealandica) are considered New Zealand’s major pasture & lawn pest and are found throughout the country.

Eggs from the grub are laid in the soil during the spring/summer months and hatch about two weeks later. The larvae feed on the roots of the grass and can grow up to about 20-25 mm long. Infested grass turns yellow/brown and dies leaving dead patches in your lawn and pastures. A close examination of these patches will show a small tunnel entrance into the soil.

The larvae are a creamy white colour and in the shape of a C with a brown head.

You will recognise adult grass grubs as a buzzing bronze Beatles that congregate in huge masses on warm still nights. They emerge around Oct, Nov & Dec months and tend to feed on shrubs and fruit trees often leaving severe defoliation.

Grass grubs can sometimes be mistaken with the Porina caterpillar. The Porina caterpillar tends to feed on the leaves rather than the roots of the grass and are easier to control. The entrance to the caterpillar tunnels is usually covered with fine webbing.

Treatment for grass grub is most effective between February and March. In late autumn/winter, the grubs are found about 2 cm from the surface. An insecticide is the most effective treatment when the grubs are underground in the soil. Trampling or rolling the grass from June onwards can also reduce the population as it damages the pupae.