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About bacterial leaf scorch

This bacterium can infect many host plants. It causes different diseases in different hosts. It affects plants important to New Zealand, like grapes, olives and citrus. The bacterium multiplies and blocks the water transport system in plants. It stops the water getting from the roots to the leaves.

It goes by many names, such as Pierce's disease in grapes, olive quick decline syndrome, and citrus variegated chlorosis.

This bacterium has killed 1,000-year-old olive trees in Italy and initially devastated vineyards in California. Although, it's now managed in California.

Global distribution of bacterial leaf scorch

World distribution of bacterial leaf scorch

Why this is a problem for New Zealand

Xylella is one of the most important plant diseases that MPI wants to keep out of New Zealand. It is an invasive bacterial plant disease that is spreading around the world. We regularly find out about new host plants that Xylella can infect.

Overseas, Xylella has caused devastating diseases in crops like grapes, olives and citrus. These are important to New Zealand's economy.

Scientists have found the bacterium in some of our native plants that were growing in California.

Map of New Zealand showing where this disease could establish

How it could get here

Xylella is spread locally by infected insects when they move to a new plant after feeding on a diseased one. It could travel internationally on infected nursery stock. MPI has strict measures in place to limit the chances of infected nursery stock or insects coming through the border.

How to identify bacterial leaf scorch

Scorched leaves are a sign of some other plant diseases already present in New Zealand. Plants infected with Xylella show:

  • scorched leaves
  • browning
  • loss of leaves
  • stunted shoots
  • reduced fruit size
  • over time, dieback and death of the plant.

 

Oleander tree showing over half the leaves brown and dead.
Oleander tree infected with bacterial leaf scorch
Image: CC 3.0 Pompilid

 

If you think you've found this disease

If you're an experienced grower and have found unusual signs of leaf scorch on host plants:

 

Note: This information is a summary of this disease's global distribution and potential impacts to New Zealand.

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