Diagnosing allelopathy in cereals

Allelopathy is an uncommon disorder of germinating plants caused by a toxins in the soil that have leached from plant residues.

Seedlings have deformed roots and shoots.
Goosefoot contains phytotoxins that leach from the dead plant

What to look for

    Paddock

  • Poor germination and spindly seedlings in patches, rows or scattered plants where the plant is in contact with plant residues.
  • Severity may vary with soil type.

    Plant

  • Seeds germinate but roots and shoot are deformed and spindly.
  • The emerging shoot frequently wanders through the soil without reaching the surface.
  • Plants that do emerge are poor and rarely produce grain.

What else could it be

Condition Similarities Differences
Diagnosing deep seeding in cereals Reduced germination, weak seedling and/or older leaf death Surviving plants recover
Diagnosing poor seedbed soil structure Reduced germination, weak seedling and/or older leaf death Surviving plants recover
Diagnosing poor seed-soil contact in crops Reduced germination, weak seedling and/or older leaf death Surviving plants recover
Diagnosing pythium root rot in cereals Root browning, stunted plants. Phytotoxins that cause allelopathy may predispose plants to pythium root rot Mostly in cold wet conditions, distinctive root lesions
Root chewing insects
Reduced germination, weak seedling and/or older leaf death Chewed root or lower stem

Where does it occur?

  • Phytotoxicity most often results from toxins leaching into the soil from dead or dying plants in the following situations:
  • Allelopathy from summer weeds such as goosefoot (Chenopodium pumilio).
  • Where previous season's crop or pasture residues are left in contact with the seed during seeding.
  • Where crops are sown into weedy seedbeds sprayed with a herbicide before the weeds have died.
  • Toxins that cause allelopathy predispose the plants to fungal root rot.
  • Toxicity tends to be worse where crops are sown in a moist drying seedbed, where there is insufficient rainfall to leach toxins through the soil profile, and in cold, cloudy weather.

Management strategies

  • There is no treatment for affected plants.
  • Allelopathy can be avoided by minimising summer weed growth and plant residue contact with the seed at sowing.

Where to go for expert help

DDLS Seed Testing and Certification
+61 (0)8 9368 3721
Page last updated: Tuesday, 20 January 2015 - 9:32am