Black rot

Guignardia bidwellii

Black rot could harm our wine industry. The disease can ruin a grape crop and spoil a batch of wine.

About black rot

This is a fungus that causes diseases on grapes and some ornamental plants. It's native to North America and parts of Europe.

Global distribution of black rot

World distribution of black rot

Why this is a problem for New Zealand

This fungus can cause up to 80% loss of a grape crop. It can spoil the taste of wine if infected grapes mix with healthy ones.

It's quite hardy and can survive harsh conditions in canes, leaves, the vine, or the ground.

Map of New Zealand showing where this disease could establish

How could it get here

The fungus could come in as a visible powder (spores) on:

  • fruit (grapes)
  • leaves
  • flowers
  • stems.

Whenever travelling to New Zealand, always declare any food or fruit in your luggage. If you fail to do so, you could face a $400 fine.

Where will I find it

Black rot is more likely to establish in the North Island.

How to identify black rot

You will see small brown circular spots on young grape leaves (older leaves can resist the rot). The symptoms on leaves can be confused with other fungi.

Black rot infects grapes when they're still green. You will see light brown spots that become dark brown. Eventually, the spots cover the whole fruit.

multiple light brown spots scattered over a leaf surface a blistered skin of a grape stem with raised black spots
Left: Close up of brown spots on a leaf. Image: CC 2.0 by Daniel Molitor
Right: Symptoms of black rot on a grape stem. Image: CC 3.0 by Clemson University – USDA Cooperative Extension Slide Series

If you find black rot

 


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

Last reviewed:
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