Scentless mayweed
Other names
Corn feverfew, dog
Latin names
Tripleurospermum inodorum (L.) Sch.Bip; (Matricaria inodora L.)
Weed Type
Annual Broad-leaved Weeds
Occurrence
A native annual or biennial weed of arable land and waste ground, common on all lowland soils except chalk. Scentless mayweed is abundant throughout the UK but the distribution is determined by the location of cultivated land. It is recorded up to 1,750 ft. It is moderately resistant to trampling and compaction but it does not thrive in high summer temperatures or drought. It is intolerant of dense shade and waterlogging. It responds to increased levels of soil fertility, particularly to applications of manure.
Scentless mayweed is a common weed of cereals, sugar beet and other arable crops. It is also a frequent garden weed.
Scentless mayweed is very variable in size and habit. Some populations have developed resistance to certain hormone herbicides. A diploid form predominates in Britain and Northern Europe. In continental Europe, a tetraploid form is predominant that may exhibit perennial growth. There is some evidence that winter and summer annual forms occur. Hybrids have been reported with other mayweed species but these were sterile.
Scentless mayweed is not palatable to livestock and is avoided by hens. It is a host of several insect pests but is also a source of nectar and pollen for beneficial insects. The sap contains an anti-viral agent that inhibits the growth of polio and herpes viruses.
Biology
Scentless mayweed flowers from June to October. It is self-incompatible in Britain and isolated plants may not set seed. The flowers are insect pollinated. Seeds start to become viable 12 days after flowering and are fully ripe 4 weeks after the outer florets open. Seed is set from August to October. Each flower head can contain 345 to 533 seeds. A plant may produce 10,000 to 200,000 seeds but figures of over a million have been quoted. There is a good correlation between seed number and plant dry weight.
In the laboratory, a period of dry-storage increases seed germination. Germination is also stimulated by light. Scentless mayweed is shallow germinating because it requires repeated diurnal exposure to light over a period of days to stimulate germination. Wetting and drying of seeds in field conditions may influence the light requirement and encourage germination in the dark. Seeds of diploid and tetraploid plants exhibit similar temperature limits for germination. The upper limit is 40°C and the lower is 5°C. However, tetraploid seeds germinate better at suboptimal temperatures and this may allow a more northerly distribution.
In the field, scentless mayweed germinates through most of the year with peaks of seedling emergence in spring and autumn. The main flush is from February to May with a smaller one in October. In a sandy loam soil, field seedlings emerged from the top 30 mm of soil with over 80% coming from the surface 0 to 5 mm layer.
Seedlings that emerge from January to June take progressively longer to reach flowering. Those that emerge after August, overwinter as rosettes and flower in spring. Daylength is the controlling factor. Seedlings and leaf rosettes are frost tolerant but flowering shoots may be damaged.
Persistence and Spread
Scentless mayweed seed buried in a mineral soil and left undisturbed had up to 52% viability after 4 years but none was viable after 20 years. The viability of seed mixed with soil had declined by 77% after 6 years if left undisturbed but by 90% if cultivated periodically. Seed sown in the field and followed over a 5-year period in winter cereals showed an annual decline of 80%. Emerged seedlings represented 15% of the seedbank. Seed buried in a peat soil for 20 years retained 8% viability. Seed recovered from excavations and dated at 25 years old is reported to have germinated. Dry stored seed gave 92% germination after 1 year and 21% after 5 years. Seed stored under granary conditions had 59% viability after 1 year but only trace viability after 4 years.
There is no obvious dispersal mechanism and seed may simply fall to the ground. In cereals, the seed is readily dispersed by the combine harvester during crop harvest. Seed may be transported with hay and straw or in mud on tyres and footwear. Scentless mayweed seed has been a contaminant in grass, clover, vegetable and cereal seeds, particularly home saved seed. Seeds survive passage through ruminants and viable seeds have been recovered from cattle dung. Seeds float for 12 hours or more in fresh and seawater, and retain 75% viability after submergence for 220 days.
Management
Control is by surface cultivations in spring and summer and by the inclusion of root crops in the rotation. The aim is to prevent seeding. Late autumn and early spring tillage is effective in controlling scentless mayweed before drilling. In winter wheat, increasing crop density will reduce seed production due to the effect on weed growth. Regenerated shoots may flower and set seed in uncultivated cereal stubble.
Cultivation in the dark does not reduce seedling emergence as the seeds require more than a single light flash to stimulate germination and seeds in the surface soil will germinate anyway if conditions are favourable.
Seed numbers in soil have been reduced by 50% following a 1-year fallow. An application of lime may help to reduce the weed on deficient land.
Scentless mayweed seedlings are relatively tolerant of flame weeding. Seeds in field soil are killed by steaming at 60°C.
A number of insect species feed on scentless mayweed. Insect larvae destroy a significant number of the seeds in the flowerhead and mine the stems and leaves.
Updated November 2007.