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Grass Grub

Grass grub is found throughout New Zealand and is considered New Zealand's major lawn pest. It attacks the roots of grasses and other plants.


Grass grub is found throughout New Zealand and is considered to be New Zealand's major pasture and lawn pest. Grass grub lawn damage shows as patchy areas of dead grass; usually seen from March. It will laso attack the roots of other plants including pot plants.

Eggs of the New Zealand grass grub are laid in the soil during spring/summer (Nov-Dec); normally hatching after about 2 weeks. The small larvae then feed on the roots of grasses until spring, growing to 20-25 mm long. Infested turf and pasture turns yellow and dies off leaving a dead mat of turf.

In October, November and December when the adults emerge from their pupae, massed flights of soft buzzing slow flying beetles often occur on still warm nights. Later these bronze beetles congregate in huge numbers, they feed on fruit trees and shrubs which are often severely defoliated.

During the late autumn and winter the grubs do not eat in the top 5cm of soil. The grubs are usually found about 15 cm below the surface and control of the grub requires getting insecticide to this level in the soil. Treatment is most effective from February to March.

Tasmanian grass grub are damaging grubs from March to December. Their damage is typically patches of bare soil which appear from autumn to late winter. These can be small areas 100 mm in diameter on lawns or bowling greens. Examination of the soil surface will reveal the tunnel entrances (3-5 mm in diameter) through which the grubs emerge. This damage is easily confused with that caused by the porina caterpillar. A difference is that porina covers its droppings and dug out soil around its tunnel entrance with fine webbing.


To get rid of grass grub follow these steps:

Apply LawnPro Lawnguard Granules on the grass paddock and lawns you wish to protect from grass grub. Ideal for use from February to late Autumn but can be used effectively through to Spring and Summer. The prills must be watered in, so sprinkle before moderate to heavy rain (13 mm) or water the area thoroughly after treatment with a sprinkler.

To control adult beetles (brown beetle) spray foliage of affected trees and shrubs with Kiwicare PLANThealth Spectrum or Insect Hit between October and January. 

Then apply LawnPro Smart Patch Mix, LawnPro Lawn Thickener or LawnPro Smart Lawn Seed to repair the lawn and fill in patches of dead or affected lawn.

Did you know

Other similar lawn damaging insect larvae include porina, armyworm, leather jackets, wireworm and greasy cutworm.

The scientific name of bronze beetle (grass grub) is Costelytra zealandica


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