Waratahs are susceptible to many pests and diseases. The most damaging are the root rot diseases, caused by the introduced Phytophthora fungus. This disease is characterised by desiccated light brown leaves and a withered stem.
Over- and under-watering and excessive use of fertiliser can predispose plants to these diseases. Be vigilant for insect infestations. Moth-borers, which bore into the flower buds and destroy the developing flowers, are most active during the autumn and winter months. White Palm Scale (Phenacaspis eugeniae) is active during warmer times of the year.
White Palm Scale, Pseudaulacaspis eugeniae (Maskell), is the common scale found in Waratahs in and around Sydney. This is also called Oleander Scale and Waratah Scale. It is a type of hard scale.
How to detect the presence of scales in a bush
When spots (discoloured patches) appear on the upper surface of leaves, the lower surface of leaves should be checked for the presence of the scales. Another indicator for the presence of scales is the presence of ants on the bush, particularly when the flowers are infested. The ants feed on the honey dew secreted by the scales as excreta, and they tend to congregate around the scales.
How to manage scales on Waratahs
- Biological. There are predators like ladybird beetles and which attack and feed on young and adult scales. There are also tiny wasps which parasitise scale insects. They pierce through the white armour of the adult females with their needle like ovipositor and lay their eggs into the fleshy bodies of the scales.
- Mechanical. If only few bushes are infested, scrubbing and scraping the plant surface where the scales are found will dislodge the scales. Once dislodged, they will starve and die as they dry out exposed to the air. Or use secateurs to cut off an affected branch.
- Chemical. Spraying affected plants with an approved pest oil will help to suffocate scale. Repeat sprays will be necessary.