rayless chamomile, rayless mayweed
Matricaria discoidea DC.; (M. suaveolens, M. matricarioides, Chamomilla suaveolens)
An introduced annual weed of wasteland and bare places by paths. Pineappleweed was introduced into the UK just prior to 1900 and within 25 years it had spread along roadsides throughout most of England. Pineappleweed is now common throughout the UK, and is still increasing, especially on tracks and paths and on cultivated land. It prefers an open loamy or sandy loam soil.
Pineappleweed occurs in cereals and broad-leaved arable crops and has become a frequent weed of intensive vegetable crops. It is also a common garden weed.
Pineapleweed is used medicinally, including as an effective worming treatment. The flowers smell of pineapple when crushed.
Pineappleweed flowers from June to September, sometimes into November. Insects seldom visit the flowers. Seed is set from July onwards within 40-50 days of flowering. The average seed number per plant ranges from 850 to 7,000. The 1,000 seed weight is 0.13 g.
Seed germination is promoted by light, just a short flash is sufficient. In the laboratory, germination is increased by a period of dry-storage. Seed sown in field soil and cultivated periodically emerged from February to November with peaks from March to May and August to October.
Plants emerging from January to April remain vegetative for longer before flowering than plants emerging from mid-May to mid-July that take just 40-50 days to flower. All set seed and die before winter. Plants that emerge after August are likely to overwinter as vegetative rosettes that do not flower until the following spring. Daylength is the controlling factor and flowering is delayed at a shorter daylength.
In sandy loam soil, seedlings emerge from the top 0-10 mm of soil with the majority emerging from the surface 5 mm.
Based on seed characters, pineappleweed seed should persist for longer than 5 years in soil. Seed mixed with soil and left undisturbed declined by 83% after 6 years but in cultivated soil the decline was 91%. Seed buried in sub-arctic conditions had 20% viability after 6.7 years.
Seeds are dispersed in mud and by rain splash. Mud on the tyres of cars was responsible for much of the early spread. The seeds are light enough to be blown by the wind and by passing traffic. Viable seeds have been found in horse droppings.
Seedlings and larger plants should be controlled by cultivation and hand weeding to prevent seeding. Pineappleweed seedlings are more numerous on tine-cultivated or no-till land than ploughed land.
In grassland, pineappleweed is able to colonise areas around gateways and troughs where livestock have trampled and caused poaching.
Seedlings with 2-6 leaves are tolerant of flame weeding.
Updated October 2007.