Euphorbia exigua L.
Dwarf spurge occurs on arable land but rarely elsewhere and is probably native. It is not recorded above 1,000 ft in the UK.
Dwarf spurge is a variable annual weed of cornfields that appears to be discouraged by root crops. In an early survey of Bedfordshire and Norfolk it was chiefly found on clay and heavier loams but was often scarce. It is commoner in S & E England and is considered to be more frequent on calcareous soils. In a study of seedbanks in some arable soils in the English midlands in 1972-3, dwarf spurge was recorded in 31% of the fields sampled in Oxfordshire and 13% of those in Warwickshire but it was never present in large numbers. In seedbank studies in arable fields in France, dwarf spurge was well represented in the seedbank and the emerged vegetation.
When damaged, the plant exudes a milky sap that can be a severe irritant on contact with the skin. The oil contained in the seeds is a drastic purgative. The active principles in the seeds and foliage are not affected by drying.
Dwarf spurge flowers from June to November. In a limited study of seed dynamics, seedlings emerged chiefly in winter but other evidence suggests that spring is the main period of germination.
Seed longevity in soil is 6 to 7 years. Dwarf spurge seed sown in the field and followed over a 5-year period in winter wheat or spring barley showed an annual decline of around 40%. Emerged seedlings represented 8% of the seedbank.
Surface cultivations in spring and the normal tillage associated with root crops keep dwarf spurge in check. Seedling emergence occurs only over a limited period in late-winter to spring and hoeing and crop competition reduce seed return.
Seed numbers in soil were reduced by 50% following a 1-year fallow and by 90% if this was continued for a second year. However, there was a similar reduction in seed numbers when land was cropped with winter wheat for this period. Fallowing every 5 years over a 15-year period reduced seed numbers by up to 90% after the first fallow year. This level of seed numbers was maintained after subsequent fallow years although seed numbers may have increased during the intervening cropped years.
Updated October 2007.