Grass Grub Larvae
Costelytra zealandica
Grass grub (Costelytra zealandica) is the larval stage of the bronze beetle and is found throughout New Zealand from Southland as far north as Waikato. Grass grubs feed on the roots of pasture and autumn planted cereals and can cause extensive plant death if not controlled. Grass grubs have three larval instars and each one is capable of causing damage but the third instar, which is usually between February and spring, is the most damaging. Not all the larvae at their largest but this also coincides with plant establishment. The treatment threshold for grass grub is two grubs per spade square. Well before sowing, take a garden spade and dig ten sample squares to the depth of the spade blade in a diagonal across the paddock. Sift through the soil and if an average of more than two grubs per sample is found treat with an effective seed treatment.
