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Lilly pillies are commonly used for hedging and screening. While they are are not difficult to grow, they can fall sick due to factors like inadequate growing conditions, pests and diseases.
Being such a popular plant, we get lots of questions from Bunnings Workshop community members about how to identify and treat problems with lilly pillies.
Here are some common reasons why lilly pillies decline in health and expert advice on how to diagnose and care for your plants.
Pests
Lilly pillies belong to the plant family Myrtaceae. This is the same family as eucalypts, willow myrtles, turpentine, bottlebrushes, paperbarks and tea trees. Lilly pillies are subject to many of the same pests and diseases as their relatives.
Stressed lilly pillies can usually be fixed with the right attention. Providing optimal growing conditions for your plants, choosing varieties suited to your area and providing optimal growing conditions for your plants will usually help keep pests at bay.
To prevent pest infestations, ask a garden specialist at your local Bunnings store which varieties are recommended for your climate and soil type. You can also have a look at the Bunnings guide How to grow and care for a lilly pilly for more information on different varieties.
Below are some frequently asked questions related to the different types of pests that lilly pillies commonly attract and how to get rid of them.
Why are my lilly pilly leaves pimply?
Psyllids are small, sap-sucking insects (sometimes also called plant lice) that cause ugly pimple-like deformation of new lilly pilly leaves, mainly on Syzygium varieties. These appear mainly on the upper surfaces of leaves with comparable dimples on the undersides.
Often the pimples are distinctly reddish-purple but sometimes appear only as crinkling or puckering of the leaves. The psyllid nymphs, sometimes called lerps, are visible on the back of leaves as white, fluffy or waxy scale-like dots. Just be careful not to confuse them for scale.
How to care for lilly pillies affected by psyllids
If psyllid damage is minimal, prune off and collect all affected foliage, seal it in a bag and dispose of it in the household rubbish.
Spraying all infested foliage on shrubs and trees with eco-oil as directed on the label may assist in controlling the insects. Make sure to wet the undersides of the leaves as well as the top.
What are the small white things on the back of lilly pilly leaves that can be scraped off?
Scale appears on the undersides of leaves and on stems and branches. The outer, waxy covering shields a small insect that sucks sap, sometimes causing blemishes on the upper surfaces of leaves as well.
Some lilly pillies are more susceptible to scale attacks than others, but in general this pest is not of major concern when plants are maintained in optimal health with good growing conditions. Regular trimming to encourage new growth also helps. Plants in poor health or reaching an old age may succumb more readily to severe infestations.
How to treat scale on lilly pillies
If a small incursion of scale is noticed, get on to it as quickly as possible using a combination of insecticide and horticultural oil spray such as Yates Scale Gun Insect Pest Killer. It includes pyrethrum and white oil. The oil aids in dissolving the waxy scale and smothering the pest underneath the wax cap while the pyrethrum kills the pest. 
It's essential to get a good cover over affected areas, making sure to spray the undersides of leaves and along branches, as well as on the upper surfaces of leaves where the scale may be more obvious. Repeat in 10-14 days to ensure good control.
Why are my lilly pilly hedges full of ants?
If your lilly pillies are covered in ants, you will almost certainly find scale on the leaves and stems. Ants derive a great source of food from the sweet honey-dew secretions of scale insects.
How to get rid of ants on lilly pillies
To get rid of ants on lilly pillies, control the scale and the ants will soon move on.
Diseases
Lilly pillies, like most plants, become more prone to disease outbreaks when they are stressed or not looked after well.
Make sure you understand their requirements and choose plants that come recommended for your specific conditions.
Below are some frequently asked questions on how to identify and treat common lilly pilly diseases.
What is the black powder all over the undersides of the lilly pilly leaves?
Black powder on the underside of lilly pilly leaves is sooty mould, a black or dark grey-brown fungus that grows on the sticky honey-dew secretions of scale insects and other sap-sucking pests.
How to treat sooty mould on lilly pillies
To treat sooty mould, control or completely eradicate the scale and the mould will disappear too. There is no need to apply fungicides for this problem. 
What is the yellow pollen-like dust on the leaves of my lilly pilly hedge?
Myrtle rust (Puccinia psidii) is a recently introduced fungal disease which infects plants in the Myrtaceae family.
The fungus attacks new leaves, shoot tips and young stems, with its severity and symptoms varying depending on the host species.
Generally, myrtle rust starts as small purple spots on leaves, but these are often not noticed until bright yellow spores form in pustules within these spots. The pustules fade to dull yellow and then grey as the infection ages. In severe infections, spots enlarge and merge, often causing leaf distortion. Heavy infection can result in the death of soft plant material.
How to treat myrtle rust on lilly pillies
Precautions to limit the spread of myrtle rust should always be taken.
It can be controlled in the home garden with applications of copper fungicide or mancozeb. Please follow all product and safety instructions on the label before usage.
Problems with pruning and watering lilly pillies
Most problems with lilly pilly hedging come when shaping and regular pruning begins. The aim is to not only neaten the plants by cutting to a standard height and width, but also to encourage masses of new growth tips that will provide a colourful spectacle throughout the year.
Lilly pillies should also be closely spaced and watered and fed generously in the first few years to encourage strong, dense growth. The Bunnings guide How to plant and propagate lilly pillies contains more information.
Below are frequently asked questions related to pruning and watering lilly pillies.
Why does my lilly pilly hedge look dead?
It’s a fine line between trimming the new growth and cutting too hard into old wood. Complete removal by cutting back into older wood will take off all new growth. If it’s done often enough, it will discourage new shoots to the point where you’re left with what looks like a dead hedge. By that stage, it is probably too late to reverse the damage. Follow the directions below to prune your lilly pilly hedge.
How to prune a lilly pilly hedge
The aim of pruning the hedge is to just nip the growing tips back a little every few weeks or months, not to remove them entirely.
For more advice on pruning lilly pillies, check out the Bunnings guide How to maintain healthy lilly pillies.
Why are the leaves on my lilly pilly hedge curling?
Curling leaves are usually a sign of either too much or too little water.
Making sure a hedge is well watered can be difficult, because the root spread of each plant is likely to be much greater than the depth of the hedge, sometimes extending at least a metre of so beyond the hedge line.
If you are watering directly under the hedge itself, then the moisture-seeking roots may be going dry.
How to water a lilly pilly hedge
Water at least a metre either side of the hedge wherever possible, especially over summer when rainfall may be scarce.
Check out my guide How to diagnose a sick plant for more information on how to tell if your plant is underwatered or overwatered.
The Bunnings Workshop community is here to help if you need more help with your lilly pilly. Don’t hesitate to ask a question.
