Euphorbia helioscopia L.
Sun spurge is an annual weed of cultivated fields and waste places on sandy and clay loams. It prefers light land. Sun spurge is common throughout the UK especially in lowland areas. It is recorded up to 1,500 ft in Britain. In an early survey of Norfolk and Bedfordshire it was found mainly on chalk and calcareous soils. Sun spurge occurred in 8% of cereal crops but was most frequent in barley. It was rarely found in peas and beans. Sun spurge is a common garden weed.
Sun spurge bleeds a milky sap when cut that can be a skin irritant. The seeds contain an oil that is a violent purgative in man and animals. The active principle in the seeds and foliage are not affected by drying. Sun spurge accumulates boron and may enrich compost to which the weed is added.
Sun spurge flowers from May to October. The average seed number per plant is 257 but there may be up to 700.
Seedling emergence occurs from April to October with most emerging from April to August. Light does not appear to have a stimulating effect on germination.
Seeds mixed with soil and left undisturbed had declined by 71% after 6 years but in cultivated soil the decline was 96%. Seed buried 24 cm deep in soil was still viable after 22 years. Seed recovered from excavations and dated at 30 years old is reported to have germinated.
Sun spurge seeds are dispersed explosively when ripe. The seeds bear a caruncle that is attractive to ants and this may aid further dispersal. Sun spurge seed can occur as a contaminant in crop seeds. In a survey of weed seed contamination in cereal seed at the time of drilling on farm in spring 1970, sun spurge seed was found in 2% of grain samples. All of the contaminated samples were from home saved seed.
Surface cultivations in spring and the tillage associated with root crops will keep sun spurge in check. It is important to prevent seeding.
Updated October 2007.