Pests and diseases of avocados

Find out about biosecurity for avocados from Plant Health Australia.

Pests

• Helopeltis
• Queensland fruit fly
• Red-banded thrips
• Red-shouldered leaf beetle
• Swarming leaf beetles
• Leaf roller

The Avocado Problem Solver Field Guide produced by Avocados Australia provides detailed information for identifying and managing the 100 insect pests, diseases and other disorders that affect avocado in Australia.

Fruit-spotting bug and banana-spotting bug

Fruit-spotting bug and Banana-spotting bug cause similar damage. Either one or both species are found in all Queensland avocado growing areas. These are serious pests which sting the fruit at all stages from fruitset until picking.

Symptoms:

• fruit shedding (if stung when small)
• fruit distortion and dimpling
• woody 'stones' where stung.

The pests have hundreds of alternate hosts and are very mobile so can quickly re-infest after a spray. They will move out of sight when you approach so are difficult to spot. A fresh batch will often fly into an orchard on a hot windy day.

By observing where damage is worst you may be able to identify 'hot spots' in your orchard which can be used for subsequent monitoring. Regular sprays of a registered insecticide are generally needed but once you become confident with monitoring it may sometimes only be necessary to spray the hotspots.

Diseases

• Cercospora spot
• Stem end rot
• Phellinus noxius root rot

Anthracnose

Anthracnose is caused by the fungus Colletotrichum gloeosporioides and presents as a fruit rot that remains latent until the fruit ripens.

Fruit infected with anthracnose can rarely be identified at packing and is usually only discovered at the point of preparation by the consumer.

Just like other varieties, Hass is vulnerable to anthracnose but difficult to detect until it is cut because its thick dark skin masks the symptoms.

Management includes regular orchard sprays (every 2-4 weeks depending on weather conditions) from shortly after fruitset until harvest using a registered protectant fungicide such as copper oxychloride.

Controlling root rot

Avocado trees are very susceptible to root rot, caused by the soil-borne fungus Phytophthora cinnamomi. Without root rot management the tree will lack an adequate root system and can't perform.

Effective root rot control methods:

• disease free nursery trees
• using more tolerant rootstocks
• good drainage which includes the use of tree mounds
• mulching and good soil health
• appropriate soil moisture management
• chemical treatment
• good nutritional practices including sufficient calcium
• suitable soil pH.

Treatment

Phosphonate fungicide is the best chemical root rot treatment, both as a regular preventative treatment and to cure the disease.

You must maintain an annual, or in some cases biannual, treatment with phosphonate.

You can apply the fungicide to the leaves (only if the trees are healthy) or inject it directly into the tree by trunk injection. If trees are too small to inject with phosphonate fungicide, you can use foliar sprays of phosphorous acid or metalaxyl granules on the ground. The main window for applying phosphorous acid is in autumn once the summer leaf flush has hardened. A shorter window is available in late spring once the spring leaf flush has hardened.

Seek specialist advice on the correct use of phosphonate because timing, rates and method are critical.

Watch the Protecting your avocado trees from Phytophthora root rot video for the steps to apply phosphorous acid correctly.

Replanting

It is difficult to get a replant tree to grow where the original tree has died from root rot.

If the trees either side of the gap won't effectively colonise the space:

1. Select a planting site at least 2m away from the site of the dead tree and prepare the site for replanting.
2. Dig it over, check the pH and apply lime or dolomite and organic manure as required.
3. Mulch the site and leave for at least 3–6 months (or more if possible) before planting.
4. Apply metalaxyl granules around the tree at planting and again 8 weeks later.
5. Adjust the irrigation emitter and fertiliser rate for the smaller size of the newly planted tree.