chickenwort, craches, maruns, winterweed
Stellaria media L. (Alsine media)
Common chickweed, an annual or overwintering native plant, is one of the commonest weeds of cultivated land in the UK. It also occurs on roadsides, shingle riverbanks, coastal cliffs and in gardens. It is widely distributed over all soil types but is more abundant on lighter soils. It is favoured by high potassium levels and is indicative of high nitrogen and low phosphate and lime levels. It is absent from the most acidic soils. It thrives in areas of soil disturbance and declines when cultivation ceases for a long period. It is sensitive to drought and is one of the first weeds to wilt in dry conditions.
Common chickweed is a frequent weed of cereals, sugar beet and other arable crops. It grows best in cool, humid conditions and is a serious problem in overwintered vegetable and flower bulb crops.
Common chickweed can be very variable in size, habit and general appearance. Some of this may have a genetic basis and some may be due to soil and environmental effects. Summer and winter forms with different growth habits are thought to occur. In the past, common chickweed was often grouped with the closely related species S. neglecta and S. pallida. Three subspecies are recognised but only ssp. media occurs in the UK. Common chickweed populations have been found with resistance to the phenoxy-herbicide mecoprop and to certain sulfonylurea herbicides following repeated use of the chemicals.
Common chickweed is a host of several damaging virus diseases of crop plants. Some viruses can be carried in chickweed seeds that will grow into infected plants. The virus can persist for at least 5 months in seeds buried in soil. Several important nematode species can infest common chickweed.
The weed is an important constituent in the diet of many farmland birds. It has medicinal and therapeutic uses, is rich in vitamin C and may be eaten as a salad vegetable. It can accumulate nitrate and may become toxic to stock. In addition, it has a relatively high oxalic acid content and a low level of calcium that may have an adverse effect on dietary calcium bioavailability.
Common chickweed flowers and sets seed all through the year. It has been known to flower and ripen seed under a snow-cover 10-20 cm deep. Flowers are normally self-pollinated but there is a short period when insects can effect cross-pollination. In winter, flowers are produced that do not open making self-pollination inevitable. Stems cut off in flower do not produce viable seed but any green immature capsules present will ripen and the seeds within them can become capable of germination. Individual seed capsules contain around 10 seeds and the average seed number per plant is 2,200 to 2,700. However, plants with 25,000 seeds have been recorded. There is a good correlation between seed number and plant dry weight. Common chickweed can complete its life cycle in 5-6 weeks.
Seeds will germinate at any time of year but particularly in spring and autumn. Germination can occur between 2°C and 30°C but the optimum temperature is 15°C. Seed collected from separate plant populations may differ in size and germination characteristics. Some seeds can germinate immediately after shedding. Buried seeds develop a light requirement for germination. In the field, seedling emergence declines with increasing depth of seed burial. Most seedlings emerge from the surface 30 mm of soil. Seedlings from seeds buried deeper in the soil take longer to emerge. Chickweed is able to grow at relatively low temperatures and seedlings can survive all but the severest frosts.
Buried seeds are known to retain viability for at least 25 and probably over 40 years. Seed buried in soil for 10 years gave up to 22% germination. Seeds in dry storage for 30 months at low temperatures retained full viability. Common chickweed seeds broadcast onto the surface of clay and silty-loam soils, ploughed to 20 cm or flexible tine cultivated to 10-15 cm and followed over a 6 year period of cropping with winter or spring wheat declined at an annual rate of 35%. The estimated time to 95% decline was 7-8 years depending on the frequency of cultivation. In a series of autumn-sown crops the time to 99% decline of seed in the soil seedbank was 11.1 years. The mean annual decline rate was 30%. In other studies in cultivated soil the annual percent decline was 41%. Elsewhere, under a grass sward, common chickweed seed had a mean annual decline rate of 26%.
The seed capsule splits when mature and the seeds are shaken out onto the soil beneath the parent plant. The seed is dispersed further in mud on footwear and tyres. Ants also carry seeds away. Common chickweed seed was a common contaminant in cereal, grass, clover and other crop seeds. It remains a problem in home-saved cereal seed.
Chaffinches eat common chickweed seeds readily. A small number of seeds survive passage through the digestive system of small birds and germinate in their droppings. Seeds are also found in cattle, deer, horse and pig droppings and in worm cast soil. Apparently-viable seeds have been found in cattle manure. Ants can also transport seed. Seed has been recovered from irrigation water. The seed can withstand submergence in seawater.
In cool wet conditions common chickweed forms a dense mat of spreading stems that may root at the nodes making it difficult to hoe or pull up. Hoed plants will root again in moist soil. Complete burial is the most effective treatment. In root crops, control is by repeated surface tillage in hot, dry weather. In cereals, increasing the sowing rate and reducing the row width help to suppress chickweed growth. Spring-tine harrowing in July is said to give good control of the weed. After cereal harvest, stubble cultivations give good control of freshly shed seed. The soil should be worked to a depth of 5 cm at 14-day intervals. Common chickweed often emerges in winter when ploughing will destroy it.
Mowing is not effective with this procumbent plant and may help the weed by removing the shading effect of taller species. On newly sown leys grazing by sheep may to help to suppress common chickweed. It is grazed by many wild and domestic animals. Geese are said to eat common chickweed selectively in certain crops.
A layer of compost or cover crop residue spread over the soil will reduce common chickweed emergence. Leachate from composted household waste inhibits seed germination. There are indications that shallowly incorporating chopped straw after cereal harvest reduces seedling emergence. This may be due to the release of toxins as the straw decomposes. Seedling numbers increase, however, following applications of organic manure.
Seed numbers in soil were reduced by 85% following a 1 year fallow and by almost 90% if this was extended to 2 years. The land was ploughed, disked and harrowed during each fallow each year. Weed numbers were reduced but to a lesser extent by cropping with winter wheat for the same period and carrying out normal control measures. Fallowing at 5-year intervals over a 15-year period did not reduce seed numbers in soil further because during the intervening cropped years the weed was able to ripen seed during cropping, after harvest and before ploughing took place. Seed that remained dormant in the soil during the fallow period allowed the weed to survive through to the next crop year and increase again. Even a 4-year fallow did not eliminate all the common chickweed seeds in the soil.
Common chickweed seedlings with 2-6 leaves are relatively susceptible to flame weeding and the seeds are killed by soil solarization. Seedlings are very sensitive to UV-B radiation.
The seeds of common chickweed are consumed by several species of ground beetle. The fungus Peronospora media may be an important agent in the natural control of common chickweed.
Updated November 2007.