Allellopathy is a disorder of germinating plants caused by plant phytotoxins.
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 or amount of plant residues.
Plant
Seeds germinate but fail to reach the surface, or appear later with yellow cotyledons and new growth.
The hypocotyl is thickened and bent, often to the extent that the plant fails to emerge or emerges then re-enters the soil.
Roots are grossly distorted and reduced.
Affected seedlings usually slowly die, leaving an overall reduction in plant density
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.
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.
Toxins that cause allelopathy predispose plants to fungal root rot.
Lupins have been affected in a silo by toxins released by green wild radish seed that was harvested with the seed.
Management strategies
Weed and pasture control
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.
