Ryegrass bunt

Tilletia walkeri

This fungus could damage New Zealand's arable industry, reducing crop yield for both ryegrass and wheat.

About ryegrass bunt fungus

This fungus causes a disease called ryegrass bunt. So far, it has only been found in the United States and Australia. The symptoms are similar to Karnal bunt, which isn't present in New Zealand either. Bunt diseases leave a black powder (spores) in the seeds, reducing their quality.

In the United States, ryegrass bunt has been found in wheat seeds, where ryegrass is grown in rotation with wheat.

Global distribution of ryegrass bunt fungus

World map showing distribution of ryegrass bunt

Why this is a problem for New Zealand

In the year ended June 2018, ryegrass seed exports earned New Zealand $55 million. Our ryegrass and wheat crops would suffer if this disease arrived in New Zealand. We're keeping a lookout for this disease as it is present in Australia.

How it could get here

Ryegrass bunt is most likely to get to New Zealand in infected seeds. It could also arrive in contaminated soil on poorly-cleaned items, such as farm equipment.

Biosecurity New Zealand has strict measures in place to limit the chances of ryegrass bunt making it through the border.

How to identify ryegrass bunt

The visible symptom is a black powder (spores) in or on wheat or ryegrass seeds.

2 yellow seeds with black powdery spores magnified round spore with uneven surface
Left: Two ryegrass seeds infected with ryegrass bunt. Image: Lisa Castlebury, USDA, Bugwood.org
Right: Ryegrass bunt spore magnified about 2000 times under a scanning electron microscope. Image: Jim Plaskowitz, USDA, Bugwood.org

Report suspected cases

If you think you've found ryegrass bunt:

  • photograph it
  • note location and any landmarks
  • don't touch it because you could spread the fungus
  • call 0800 80 99 66

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

Last reviewed: