Veronica persica Poiret (Veronica areolata, V. buxbaumii, V. byzantina, V. hospita, V. tournefortii)
Common field-speedwell is a decumbent annual weed recorded on cultivated land throughout the UK. Introduced and first recorded in 1825 it was probably dispersed with clover and other crop seeds. By 1870 it was described as pretty frequent in England. Within 50 years it became not only the commonest speedwell but also one of the commonest annual weeds. A frequent colonist in cereals and in sugar beet, common field-speedwell is found on all types of cultivated soils. It prefers nutrient-rich loams of pH 6.0 to 8.0. It is not recorded above 1,000 ft in Britain.
Common field speedwell flowers throughout the year and is self-fertile. The flowers are visited by insects but are often self-pollinated. Seed is set mainly from June to October but it can be found in fruit at any time of year. There are 7 to 18 seeds per capsule. The average number of seeds per plant is 2,000 but a large plant may produce up to 7,000 seeds. There may be two generations in a year. The seed rain from plants that emerged after cultivation in April extended through to July, and increased the seed numbers within the upper layers of soil from 1,720 to 37,580 per m².
Seed germinates better in the light but will also germinate in darkness. Germination increases following a period of dry storage. In the field, seedlings emerge from February to November with peaks of emergence in May and September. The majority of seedlings emerge from the surface 30 mm of sandy and clay soils with the odd seedling emerging from down to 60 mm. Seedlings from deeper in the soil take longer to emerge, prolonging the flush of emergence. Seedlings are frost tolerant.
Seed recovered from excavations and dated at 20 years old is reported to have germinated. The annual decline of seed followed in a succession of autumn sown crops, in fields ploughed annually and with seed return prevented, was 46%. The time to 99% decline was calculated at 6.1 years. Annual seedling emergence represented 4% of the seedbank. Under a grass sward, the mean annual seed decline was 18% and the half-life was 3.5 years.
There is no obvious seed dispersal mechanism. Seed is spread as an impurity in crop seed, manure and fodder. Ants are said to transport the seeds. Earthworms ingest common speedwell seeds and viable seeds have been recovered from wormcast soil.
Only clean crop seed should be sown. The best way of keeping the weed down is surface cultivation in spring, and the inclusion of hoed row crops. Stem fragments will root readily in cool, moist conditions. Growth of the weed is strongly suppressed in shade. In winter wheat, increasing the crop density reduces weed biomass and seed production.
A 1-year fallow did not reduce seed numbers in soil. In winter wheat grown over the same period, seed numbers increased. Fallowing every 5 years during a 15-year period did not reduce seed numbers at first but there was a progressive decrease down to 22% of the original level at the end of the study.
Updated October 2007.