Capsella bursa-pastoris L. (C. simplex, Bursa bursa-pastoris)
A native summer or winter annual to biennial weed common everywhere on cultivated land, waysides and waste places. It is widely distributed and grows on most soils, sometimes in large numbers. Shepherd’s purse is a common garden weed. It has been called the second commonest flowering plant on Earth. In early surveys of Bedfordshire, Norfolk and Hertfordshire, shepherd’s purse was common and universally distributed on all soils but was probably most frequent on light and sandy land. It is infrequent on grassland except in bare areas and is absent from wetland. Shepherd’s purse is adapted to a wide climate range and will grow in sun or shade. Shepherd’s purse has been recorded up to 1,750 ft in the UK.
Flowering and fruiting occur throughout the year but are most frequent from May to October. There are 10-12 seeds per capsule and an average of 4,500 seeds per plant, although much higher numbers have been recorded. Seed size varies considerably both within and between populations. Plants growing in adverse conditions produce fewer but larger seeds. Flower spikes cut prematurely produce viable seeds from the large unripe seed capsules but not from smaller fruits.
Seeds from both dead-ripe and green capsules require a period of after-ripening before they will germinate. A period of stratification followed by exposure to light is needed to relieve dormancy and promote germination. The temperature during after-ripening can affect the temperatures at which seeds will germinate.
Seed buried in soil can remain viable for 35 years or longer. In a succession of autumn crops over a 3-4 year period, in fields ploughed annually, the annual decline of shepherd
Control is by repeated surface tillage, and by the cultivations normally used in root crops to deal with tap-rooted weeds. Fewer seedlings emerge from a seedbed with larger clods of soil than from a fine seedbed. It is important to prevent flowering and seeding. The introduction of seeds in manure or contaminated crop seed should be guarded against too.
Stubble cleaning can be an effective way of reducing seed numbers in soil. The surface soil is cultivated to a depth of 5 cm at 14-day intervals. Fallowing has little effect on seed numbers in soil in the short or the long term. In reduced tillage systems seed numbers increase in the upper 15 cm of soil.
Seedlings with 2-6 leaves are tolerant of flame weeding.