Viola arvensis Murray
Field pansy is a native annual common throughout the UK on cultivated and waste ground. It is relatively drought resistant but can also tolerate wet conditions. It prefers light soils and is favoured by a low clay content and low potassium levels.
It is a frequent weed in cereals and sugar beet in the UK. It is also a common weed in Finland, Sweden, Denmark and the Netherlands. It was ranked as one of the most important weeds in winter wheat and winter rape in Europe.
Field pansy is very variable in appearance and has previously been separated into several species, it has also been confused with heartease (V. tricolor). Its morphology is affected by environmental conditions. In cereals it is upright with few capsules. In the open it has a spreading habit with abundant seed capsules.
Field pansy is edible and has been used in cooking and in herbal medicines. The leaves and flowers are rich in vitamin C.
Field pansy flowers from April to October. The flowers may be cross-pollinated by insects but are self-fertile and largely autogamous. Each seed capsule contains around 75 seeds and a plant may produce 1,500 to 2,500 seeds. An isolated plant growing in favourable conditions can produce many more seeds but in competition with a cereal crop, seed production is much lower. Plants can be found in fruit for 7 months of the year. The time from germination to fruiting is around 125 days.
Seeds follow an annual cycle of dormancy/non-dormancy but this varies with the environmental conditions during seed maturation. Seedling emergence occurs from March to December with peaks from March to May and August to December.
In a sandy loam soil, field seedlings emerged from the upper 50 mm of soil with the majority from the top 30 mm.
Seed longevity in soil is greater than 4 years. Seed mixed with soil and left undisturbed had declined by 62% after 6 years. In cultivated soil the decline was 93%. Seeds broadcast onto the soil surface, then ploughed to 20 cm and followed over a 6-year period of cropping with winter or spring wheat had a mean annual decline rate of 48% and an estimated time to 95% loss of 4-6 years.
In dry conditions some mature seed capsules split open explosively and disperse the seeds over 2 m from the parent. Other seeds remain in the capsules even after soil cultivation, leading to small but dense patches of seedlings emerging in unison.
Up to 55% of seeds remain on the plant at cereal harvest and many are collected up with the cereal straw. The seeds are dispersed when the straw is used as mulch or for animal bedding. Seeds of field pansy have occurred as a contaminant in cereal seeds. Viable seeds have been found in cattle droppings. Field pansy seeds are eaten readily by chaffinches and a small number survive passage through the digestive system to germinate in the droppings.
Care should be taken to ensure that only pure crop seeds are sown. Field pansy seedlings are destroyed by hoeing, harrowing and other cultivations. The weed is kept in check by a competitive cereal crop and the frequent cultivations possible in a root crop. There is a lower incidence of field pansy under reduced cultivation systems.
Small seedlings are susceptible to flame weeding.
Updated November 2007.