halbeardleaf orache, spreading orache
Atriplex patula L.
Common orache is a native annual weed with an erect to procumbent habit. It is found on disturbed and waste ground throughout the UK and is recorded up to 1,500 ft. Common orache occurs on all soils and can tolerate some salinity. It prefers moist fertile sites with a pH greater than 5.0.
In a preliminary weed survey in the 1970s, common orache was recorded in 37% of the areas surveyed but the frequency varied greatly. In a study of seedbanks in the English midlands at this time, common orache seed was found in 34% of arable fields in Oxfordshire and 53% of those in Warwickshire.
Common orache flowers from June to August. The flowers are primarily wind pollinated but are also visited by insects. The seeds mature from August to October. The average seed number per plant ranges from 3,000 to 16,000. The seeds are very variable in size and colour. There are large seeds that are dull brown and compressed and small black seeds that are rounded, smooth and shiny.
The brown seeds germinate readily while the black seeds are dormant. Seed dormancy is broken by chilling. Germination has increased from 0 to 90% following 2 months moist storage at 5°C. Alternating temperatures promote germination more than constant temperatures in darkness. In the field, the main period of seedling emergence is March to May with a peak in April.
In a clay soil, field seedlings emerged from the top 70 mm of soil with 90% of seedlings emerging from the surface 30 mm. In a sandy loam, seedlings emerged from the upper 45 mm with the majority from the top 15 mm.
The black seeds are more persistent than the brown ones. Common orache seeds recovered from soil beneath a 32 year old pasture were found to germinate. In field studies, common orache seedlings continued to emerge 5 years after the last fresh seeding had occurred.
Common orache seeds can be a frequent contaminant in crop seeds, particularly home saved cereal seed. It was also common in red and white clover seed. Seeds have been found in cattle droppings and seedlings have been raised from the excreta of various birds. Seeds have also been recovered from irrigation water.
Control is by surface cultivations in spring with light harrows. In root crops, vigorous and frequent hoeing of seedlings in hot weather is effective. Large plants may need to be hand pulled to prevent seeding. The introduction of seed in contaminated crop seed should be avoided.
Seed numbers in soil were reduced by 70% after a 1-year fallow. Regular fallowing every 5th year over a 15-year period has reduced numbers by 95% and maintained them at this level.
Common orache is largely absent from grazed and trampled sites.
Updated October 2007