Matricaria recutita L., (Chamomilla recutita, Matricaria chamomilla, Tripleurospermum recutita)
Annual Broad-leaved Weeds
A native annual or biennial weed that is locally abundant on sandy or loamy arable soils and waste places throughout England and Wales. Scented mayweed prefers nitrogenous soils that are poor in lime and will tolerate saline conditions. It is considered to be an indicator of loam. It is a common weed of cereals and other arable crops where it benefits from the control of more competitive weeds.
Scented mayweed is highly attractive to ladybirds that feed on aphids. Its presence also increases the incidence of other beneficial insects. It is an aromatic plant and will taint milk and dairy products if eaten by cows.
Scented mayweed was brought into cultivation as early as the Neolithic period. The species exhibits a high degree of variability and selected forms are grown commercially. Internationally it is cultivated as a medicinal and industrial crop. A deep blue oil is steam distilled from the flowerheads and used as a substitute for true chamomile. Extracts have been used in the pharmaceutical, food and cosmetic industries, and for the control of pests.
Scented mayweed can be found in flower from May to September but the main flowering period is June to July. It is usually the first mayweed in flower. The flowers are insect pollinated. The time from flowering to seed dispersal is 20-35 days. The average seed number per plant ranges from 5,000 to 17,000.
Seeds sown in field soil and cultivated periodically emerged mainly in April-May and August-September. However, odd seedlings can emerge at anytime of year. Seeds buried in soil develop a light requirement for germination but this decreases with time. In a sandy soil, field seedlings emerged from the top 20 mm of soil with over 96% of the seedlings emerging from the surface 10 mm. The optimum depth of emergence was 5 mm.
Seedlings that emerge from January to June take progressively longer to reach flowering. Those that emerge from August onwards overwinter as rosettes and flower in spring. Daylength is the controlling factor.
Persistence and Spread
A half-life of 6.5 years has been reported for seed survival in soil. Scented mayweed seed buried in soil gave 73% germination after 11 years. Seed stored under laboratory conditions gave 100% germination after 3 years.
After cereal harvest scented mayweed seed is found in large numbers in the chaff. Earthworms ingest the seeds and intact seeds have been recovered in wormcasts. More than 25% of seeds eaten by grazing cattle passed through the digestive system unharmed.
Control is through the prevention of seeding by surface cultivations in spring and summer, and the inclusion of root crops in the rotation. Scented mayweed is susceptible to hoeing and other methods of mechanical weed control. A reduction in seedling emergence has been achieved by cultivating in darkness.
Scented mayweed seedlings have shown some tolerance to flame weeding.
Scented mayweed is attacked by several insects and is an important food plant for many of them. As a medicinal herb and potential crop, biological control may not be appropriate for scented mayweed.
Updated October 2007.