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