Grass Grub (Costelytra zealandica) also known as Brown Beetle is a native species that like many biting and chewing insects has a distinct annual life cycle. The adults emerge from October through until February and lay eggs in the soil. They also feed on foliage and may occasionally strip the leaves of cherry and plum trees. The larvae hatch from the eggs after 2 weeks and then inhabit the root zone (20mm – 30mm deep) from March until June eating the roots of susceptible species. After this time they descend to a depth of 150mm – 300mm where they overwinter. The damage they cause to plant roots reduces the plants ability to uptake water and the outcome is patches of dead grass particularly through times of drought or sustained moisture stress. The grubs vary in size from 10mm – 15mm in length and are creamy white colouration with a black abdomen. Flocks of birds particularly starlings feeding in turf often indicate a heavy infestation of grass grub.
- Survey the lawn by take spade width squares in a variety of area preferably before damage is noticeable. This is best to occur during the period December or March. Tip the sod upside down and inspect the soil. If two or more grubs are found then apply Pyrifos G granules at label rates. Please treat this compound as a poison and take all necessary precautions to ensure that there is no skin contact. Apply 25mm of water within 7 days of application