Grass Grub

Grass grub is found throughout New Zealand. Alongside armyworm they are seen as one of the biggest pests when it comes to NZ lawns and pastures. Grass grub lawn damage tends to show up as patchy areas of dead grass; which is usually seen from early autumn onwards. Grass grub are also known to attack the roots of other plants including pot plants.

The 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 tends to have large patches that turn yellow and then eventually brown as it dies off leaving a dead mat of turf.

In late spring/early summer when the adults emerge from their pupae, large groups of slow flying, buzzing, bronze-coloured beetles can be seen on windless and warm nights. These beetles can then go on to congregate in huge numbers, where they will feed on and severely damage the leaves of fruit trees and shrubs.

Treatment for grass grub is most effective from September to March. The grubs are usually found about 15 cm below the surface and as a result an insecticide that can get to these depths is required.

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.