Peak Activity: March - July
Grass Grub larvae graze the roots of grass plants causing poor growth and plant
death. Yellow patches of stunted growth appear in the pasture and plants may be
readily pulled from the ground due to loss of the root system.
There are three larval stages where Grass Grub feed on grass roots. The first instar
generally feed from November through to mid January, the second instar from mid
January to late February and the third instar from late February through until late
winter. It is during the third instar stage that feeding is at its maximum, as the
Grass Grub build up fat reserves over the cooler months. During the third instar
stage Grass Grub are the most threatening to autumn sown pastures, as their development
coincides with sowing and establishment time.
In some regions in New Zealand the climate has resulted in the development of mixed
populations of one year and two year life cycle Grass Grub, which can threaten both
spring and autumn sown pasture. In this situation the second and third instars develop
and feed over a longer period.
Grass Grub generally favour regions that are summer dry with cooler winters.
Prevention and Control
- Superstrike Grass seed
treatment
- Granular insecticides sown into the root zone
- Thorough cultivation in spring
- Heavy stocking or rolling to kill larvae near the soil surface
- Heavy grazing (March-July) to reduce Grass Grub feed supply