Citrus powdery mildew

Have you seen citrus powdery mildew symptoms?

Be on the lookout for symptoms and report them to Biosecurity Queensland.

Early detection and reporting are the key elements in controlling the disease.

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General information

Citrus powdery mildew is a fungal disease that causes leaf and shoot distortion, premature leaf and fruit drop, and twig and branch dieback. Severe infection can significantly reduce tree productivity, fruit quality and yield. The disease can also be a major problem in citrus nurseries. It has been reported to cause serious damage to mandarins, particularly nursery stock, in Asia.

Citrus powdery mildew is a plant disease and is not harmful to people or animals.

Overview

Symptoms

Citrus powdery mildew is caused by the fungi Oidium citri and O. tingitaninum. Powdery mildew on other crops, though similar looking, is caused by different species of powdery mildew fungi.

Leaves

  • White 'powdery' spores develop mostly on the upper leaf surface.
  • Young leaves turn a pale whitish-grey-green.
  • The ends of mildewed leaves can twist and curl upward.
  • Young shoots can whither and die back.
  • Severe infection causes defoliation.

Fruit

  • White 'powdery' spores develop on young fruit.
  • Infected fruit fall prematurely.

Trees

  • Infection usually appears first on the new flush and immature growth.
  • Plants can develop twig and branch dieback.
Hosts

All citrus cultivars can be affected, though some cultivars appear more susceptible than others. In India, the citrus varieties that are most susceptible are mandarins, sweet oranges and tangerines.

Spread of disease

This disease produces tiny, powdery spores that can survive on fallen leaves. It can be transported long distances by wind, on people (clothing, hands), equipment (e.g. pruning tools, mechanical harvesters or hedgers) or vehicles. Movement of infected citrus planting material poses a significant threat.

The Australian Government's Department of Agriculture, Fisheries and Forestry closely regulates approved host plant imports and monitors for illegal plant movement.

Management and quarantine

There are simple steps you can take to protect your farm:

  • Be aware of exotic citrus pest threats like citrus powdery mildew.
  • Purchase healthy propagation material from reputable nurseries that use Auscitrus seed and budwood, which is routinely tested for disease. On receipt of any new plants, check that they are free from pest and disease. If citrus powdery mildew is detected, isolate suspect nursery material from healthy plants until official checks are completed.
  • If you have been to an overseas country that has citrus powdery mildew, do not wear your travel clothes into any nursery or orchard until after they have been washed in hot soapy water.
  • Keep your farm clean. Use good sanitation and hygiene practices. Remember - workers, visitors, vehicles and equipment can spread diseases. Make sure equipment is clean before it enters your farm.
  • Check your crop. Make sure you and your farm workers are familiar with symptoms of citrus powdery mildew.
  • Report anything unusual.
Distribution

The disease is common in parts of Asia where it is prevalent in shady, poorly ventilated orchards. There have also been reports from Uganda, Israel, Central and South America and the United States (California). Citrus powdery mildew is not known to occur in Australia.

Reference and acknowledgement

Citrus powdery mildew fact sheet (PDF, 395.1KB)

Sandra Hardy (NSW DPI), Paul Holford (University of Western Sydney) and Andrew Miles and Ceri Pearce (Biosecurity Queensland, Department of Agriculture and Fisheries).

Last updated 24 April 2015