Frequently asked questions about the pests and diseases of citrus

Should I be using intergrated pest management (IPM)?

There is no simple answer to this question. Integrated Pest Management (IPM) has some very significant advantages and we would like to see all growers move into IPM as soon as possible. However, it does have some risks and is not foolproof. It requires a very high level of management to achieve the advantages on offer. We suggest you read the available material on IPM and then discuss your transition to IPM with a citrus pest consultant.

Why are the leaves of my citrus tree turning yellow?

If all the leaves on the tree are turning yellow, the problem is most likely root rot or collar rot caused by the Phytophthora fungus. Winter yellows is another but less common alternative. If the yellowing leaves are accompanied by some dieback of the twigs on Hickson mandarin, the problem will most likely be crotch rot. If only some leaves are going yellow, the problem is most likely to be a deficiency of zinc, magnesium, manganese or iron.

Why are my limes getting brown ends?

This is a problem called blossom-end rot or stylar end rot. It is mainly caused by the fruit being over-mature on the tree. As limes are meant to be harvested green, harvest the fruit before the colour begins to lighten off towards yellow. Avoid any water stress near the green harvest time.

Why are the tips of outside branches of my trees dying back?

The most likely cause is a condition known as blight, for which there is no treatment. Another cause on Navel oranges and Imperial mandarins is a disease called anthracnose. This is a stress-related problem and can only be minimised by using the copper sprays recommended for control of black spot and melanose. Root rot and collar rot can also cause twig dieback.

How do I treat borers in my trees?

There are two types of borers, each with different treatment methods. Identify which type of borer you have. If it is the more superficial trunk and branch damage from the fig and speckled longicorn beetles, scrape away any insect frass and sawdust and probe any holes with a thin flexible wire to kill any borers inside the trunk, limited damage may be controlled in this way.

The other type of borer is branch borer, which kills individual branches and leaves distinct holes in the wood. It is worse in wetter coastal areas in orchards adjacent to rainforest. With this type of borer, it is important to identify the problem early by regularly checking trees for signs of slight branch wilting. When observed, remove affected branches promptly. Regular pruning and removal of infested branches will help minimise the build up of the pest in the orchard.

There are no chemicals registered for trunk or branch borer control. Trees in a vigorous healthy condition are also less susceptible to attack.

Is there any control for Phytophthora root rot disease?

Yes. The best way to minimise the problem is to spray the foliage with phosphorous acid. Two sprays a year are recommended - the first just before flowering and the second in autumn, around late March or early April. Use the higher label rates of the chemical if you have prolonged wet weather, susceptible rootstocks, marginal soils or over watering problems. Apply the chemical in at least 8000 L/ha of water.

How do I control fruit fly?

The recommended control is the use of fruit fly bait sprays, which are mixtures of a registered insecticide, an attractant (yeast autolysate) and water. The mixture is sprayed low down on the foliage of trees as a coarse spray of about 50 mL per tree.

For multiple cropping varieties such as Meyer and Lisbon lemons, bait spraying is recommended all year round. For early varieties (e.g. Navel, Imperial), bait spraying should start in January; for mid season varieties (e.g. Ellendale, Hickson), in March; and for late season varieties (e.g. Valencia, Murcott), in May.