Onion stunt

Irregular patches of stunting in the field. Image: courtesy of Sue Pederick, SARDI

  • Also called Mallee stunt
  • Onion smut affects Allium species and cereal crops.
  • Damages the whole plant.
  • Infection develops as circular to irregular patches varying in size from 1m to 25m or more in diameter. The patches usually have distinct borders between stunted and adjacent healthy plants. Stunted onions are most obvious 6 to 12 weeks after sowing when diseased plants are less than 60 per cent the size of healthy plants. The fungus attacks the roots of young plants, pruning roots and causing rotted root tips (‘spear tipping’) and cortex.
  • Brown melanised mycelium typical of Rhizoctonia can be seen microscopically on the roots and around the basal areas of stunted plants. However, stunted onion seedlings can often appear otherwise healthy, without obvious rotted roots or root lesions.
  • Found in South Australia, Western Australia and Tasmania.
  • No movement controls are in place for this pest, but it can be prevented from entering your farm through biosecurity measures.
  • Spread through infected plants/material, soil and water.


Scientific name: Rhizoctonia solani AG8
EPPRD Category:
Life Form: Fungus

Pest Documents

FS: fact sheet

CP: contingency plan

DP: diagnostic protocol