Citrus tristeza virus

CTV is caused by a virus. There are different strains of the virus, each producing a different suite of symptoms on different citrus cultivars and rootstocks. Mandarin stem-pitting strains of CTV are particularly severe on mandarins.

Trees with severe CTV are generally stunted and have small fruit.

Mandarin stem-pitting CTV can cause a bumpy or 'ropy' appearance on tree trunks and limbs of trees. Bark can be abnormally thickened. Under the bark, stem-pitting ranges from deep to shallow pitting, and gumming. It can vary from a few small pits to many fine honeycomb-like pits.

The latter may cause no visible external symptoms on the tree trunk but twigs and branches of infected trees become brittle and may show signs of stunting or lack of vigour. While a range of other symptoms are associated with CTV, stem-pitting will be the most important symptom for detecting mandarin stem-pitting strains.

Most citrus species and cultivars are susceptible to CTV but vary in reaction-from resistant to tolerant or sensitive. Mandarin stem-pitting strains of CTV are most easily detected on mandarin or tangerine trees.

Long-distance spread can occur by the movement of CTV-infected citrus planting material, or by the movement of plant material infested with CTV-infected aphids.

The Australian Quarantine and Inspection Service closely regulates approved importations of host plant material and monitors for illegal plant movement.

Wind-borne dispersal from tropical storms and cyclones could also potentially carry infected aphid vectors from nearby countries to Australia.

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

• Be aware of mandarin stem-pitting CTV.
• Do not illegally import citrus material.
• To avoid introducing mandarin stem-pitting CTV on to your property, establish new plantings with healthy propagation material from reputable nurseries that use and routinely test their Auscitrus seed and budwood for a range of diseases. On receipt of any new plants, check that they are free from pest and disease. If mandarin stem-pitting CTV is detected, isolate suspect nursery stock from healthy plants until official checks are completed.
• Check your crop. Make sure you and your farm workers are familiar with symptoms of mandarin stem-pitting CTV and the insects that spread it.
• Report anything unusual.

Citrus tristeza virus fact sheet (PDF, 378.9KB)

Patricia Barkley (Citrus Australia Limited), Nerida Donovan and Sandra Hardy (NSW Department of Primary Industries) and Ceri Pearce (Biosecurity Queensland, Department of Agriculture and Fisheries).