Common pests
Scale
Scale insects are sap-suckers which have either a waxy or armoured covering. Juvenile scales (crawlers) disperse to favourable sites on the leaf and start feeding. The crawlers eventually become immobile, and start building their protective covers, but are still sucking the needles. This activity, if left unchecked, may eventually kill the grass tree. Control scale with an application of horticultural oil, but not during hot weather.
Mealybugs
Mealybugs often have a number of overlapping generations per year. Their development is dependent on temperatures above 25°C with high humidity. After hatching, the juveniles (crawlers) search for suitable feeding sites in sheltered areas. Control is best achieved in late October at crawler stage with a systemic insecticide such as imidacloprid or acetamiprid. Populations reach peaks during spring and autumn.
Bardi grubs
The term ‘bardi grub’ is used to describe the larva of the Longicorn beetle (Bardistus cibarius), but may also apply to other native boring larvae. A decaying trunk or a thick ‘skirt’ of dead foliage provides the perfect environment for attack by these native borers and wood boring moths. The female moth lays her eggs into this foliage and the emerging grubs bore their way into the fibrous centre of the tree. This damage disrupts the tissue that carries water and nutrients to the crown. In severe infestations the tree will rot and fall over. There is not a registered chemical control, but burning of excess foliage (thatch) every 3–4 years will make this an unsuitable haven for pests. Burning off does little damage to the green crown, as it actually promotes growth as it would in a natural fire.