Costelytra giveni

(formerly known as Costelytra zealandica)

What are Grass Grubs

Grass Grubs are the larval stage of the native Bronze (or Brown) Beetle which chew at the roots of plants and lawns. Grass grub larvae have a cream body with a light brown head and they vary in size from 6mm to 20 mm as they grow. The tail end of the grub may look darker brown which is due to the soil the grub has ingested during feeding. The grubs feed on plant roots in large numbers and curl up when disturbed.

Larvae are most active during mid spring to mid-summer, and can cause severe damage to lawns, gardens and potted plants.

Grass grubs are among the most destructive pasture pests in NZ and are a real challenge for the agricultural sector.



Wilting plants despite being well watered and brown patches in lawn, which can be easily lifted up like a carpet. 


How to protect your lawn against Grass Grubs

Yates® Lawn Grub and Porina Kill + Protect delivers excellent preventative control against grass grub larvae. For best results, apply the granules from January to March. The long residual performance of Yates® Lawn Grub and Porina Kill + Protect provides up to 6 months protection.

Keeping your lawn strong and healthy really helps it to resist pest pressure. Give your lawn a weekly deep watering, mowing at a higher level and feeding it regularly with Yates Dynamic Lifter Organic Lawn Food.

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Black Beetle

If your lawn is browning or your plants are suddenly dying, it may be the work of the black beetle or its larvae (grass grubs). Here's how to identify and control black beetles in the lawn and garden.


If the lawn is looking brown, dead or bare in patches, it's likely to be the work of the Cosmopolitan armyworm. If your vegetables are being devastated, the offender will be Tropical Armyworm, or possibly Fall Armyworm. Here's how to identify and control armyworm in your lawn or garden.

Greasy Cutworm

If your newly planted seedlings are missing or cut to the ground, it sounds like you may have cutworms in your garden. Here's how to identify and control them.


Porina caterpillars chew off lawn grass at ground level, causing it to brown and die. Here's how to protect your lawn.