Fat-hen

Fat-hen
Other names: 

goosefoot, lamb

Latin names: 

Chenopodium album L.

Occurrence: 

Fat-hen is a native summer annual found on cultivated land and waste places. It is occurs throughout Britain but is less frequent in the north and west. Fat-hen is not recorded above 1,250 ft. It is common on sandy loams and frequent on clay but less numerous on calcareous soils and gravel. It grows best on fertile soils and manuring increases its frequency.

Fat-hen is one of the most troublesome annual weeds. It is especially plentiful in potatoes, sugar beet and other root crops but less so in cereals. It is more frequent in spring-sown than autumn-sown crops. Fat-hen is also a common garden weed.

Fat-hen is a very variable plant and is sometimes treated as an aggregate species. It shows morphological plasticity in response to soil fertility and plant density. It is known to hybridise with related species but the hybrids are difficult to identify due to the variability of the main species. Some populations of fat-hen have developed resistance to some widely used herbicides.

Fat-hen was eaten as a vegetable from Neolithic times until the 16th century when it was replaced in the diet by spinach and cabbage. It is rich in vitamin C. The seeds were ground into flour. In Canada, it was grown as food for pigs and sheep. Although it can contain potentially harmful levels of nitrates, cases of poisoning are rare. It is very efficient at extracting nutrients from the soil. Fat-hen is an important constituent in the diet of farmland birds. The leaves are a source of ascaridole, an oil used to treat infestations of round worms and hook worms.

Fat-hen may act as a host to insect pests including the mangold fly and black bean aphid. It can also become infected with viruses that affect important crops. Some of the viruses can be seed-borne.

Biology: 

Fat-hen flowers in long days, usually from July to September. It is wind pollinated and the flowers may be cross or self-pollinated. Seeds are produced in abundance but mature relatively late in the season. Various figures are given for seed numbers per plant from just 10 to 164,691. Seeds mature late in the season. Seed rain from plants that emerge in April may extend from August to November.

Fat-hen produces several different types of seed on the same plant. Most seed is black and hard coated with either a rough or smooth surface. A much smaller percentage of seeds, up to 5%, are relatively large and brown with thinner, usually smooth seed coats. The brown seeds germinate much more readily while the black seeds are able to persist longer in soil. Damage to the seed coat of the black seeds will encourage germination if conditions are favourable. Plants grown from brown seeds produce the same proportions of black and brown seed as those from black seed. Immature seeds are capable of germination and may do so more readily than ripe seeds due to a thinner seed coat.

Light has a variable effect on germination depending in part on seed age and seed source. Chilling, nitrate and alternating temperatures interact with light in promoting germination. In the field, seedling emergence takes place from March to November with the main flush from May to July. The number of emerged seedlings is positively related to the frequency of soil cultivation. Most seedlings emerge from the surface 30 mm of soil with the odd seedling from down to 60 mm. However, there is a marked decline in emergence from seeds on or near the soil surface. More seedlings emerge from a fine seedbed than a rough cloddy one.

Fat-hen has a very plastic response to the environment. Plants that emerge earlier in the year tend to be larger and leafier than those that develop later. On poor soils a fat-hen plant is small and weakly, on rich soils it is tall and robust. Fat-hen is killed by frost and seedlings that emerge in the autumn rarely survive the winter. Late-spring frosts can affect seedlings that emerge early in the year.

Persistence and Spread: 

Fat-hen seed buried in undisturbed soil for 20 and 39 years gave germination levels of 65% and 9% respectively. Seeds mixed with soil and left uncultivated had declined by 47% after 6 years but in cultivated soil the decline was 91%. Seed longevity in dry-storage is 8-10 years. Seed stored in granary conditions was not viable after 20 years. Seed recovered from excavations and dated in excess of 100 years is reported to have germinated. Apparently-viable seeds of fat-hen have been extracted from the adobe walls of buildings in Mexico estimated to be 143 years old.

Fat-hen 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 had a mean annual decline rate of 28%. The estimated time to 95% loss was 6-20 years depending on the frequency of cultivation. The annual seedbank decline over 3-4 years cropping with winter wheat and OSR was 52%, and the calculated time to 99% loss was 6.3 years. In another similar trial, the annual decline rate was 40%, and emerged seedlings represented 8% of the fat-hen seed in the seedbank. The depletion of seed is greater from the surface layers of soil.

There is no obvious seed dispersal mechanism and seedlings often occur in dense patches due to seeds falling around the parent plant. In cereals, using a combine harvester has been shown to leave more fat-hen seeds on the ground after harvest than cutting the cereal with a binder and threshing the crop elsewhere. Fat-hen seed was a common impurity in commercial clover seed especially alsike clover. It was also found in vegetable and cereal seeds, especially home saved seeds.

Fat-hen seed has been found in cattle, horse and pig droppings, and seedlings have been raised from the excreta of various birds. In fact, germination was enhanced by the passage through birds. Fat-hen was the most numerous seed to survive in fresh organic dairy farm manure but numbers were reduced by 90% after composting. Some seeds can survive ensilage or rumen digestion alone but most seeds are killed by a combination of 8 weeks ensilage followed by rumen digestion. Fat-hen seeds have been recovered from wormcasts. Seed has been found in irrigation water and is known to survive a long period of submergence in water.

Management: 

The introduction of fat-hen seed in crop seed or in manure should be guarded against. Control is by surface cultivations with light harrows when cereals are 5-7.5 cm tall. In root crops vigorous and frequent hoeing of seedlings is effective in hot weather but large plants may need to be removed by hand. In newly-sown grass, fat-hen seedlings do not survive cutting or trampling.

Fresh seeding must be prevented. Repeated cultivation is unlikely to rapidly deplete the seedbank of fat-hen seed due to its dormancy characteristics. Models have been developed that simulate the population dynamics of fat-hen. These allow the result of different management strategies on seedling emergence, mortality and seed return to be predicted.

Seedlings with 2-6 leaves are killed by flame weeding. Fat-hen seed is susceptible to soil solarization and can be killed by direct heating of soil. The seedlings are moderately susceptible to ultraviolet-B radiation. Leaf area and biomass decline, shoot height is reduced and root biomass is also affected.

Covering soil with a 3 cm layer of compost reduced seedling emergence. Leachate from green-waste compost has been shown to decrease seed germination. In the field, a mulch of cover-crop residue over the soil surface reduces seedling emergence. In glasshouse trials in the USA, corn gluten meal (CGM) has been shown to reduce fat-hen survival. Corn gluten hydrolysate (CGH), derived from CGM, has been shown to be more active in reducing fat-hen development.

Many insects are associated with fat-hen and several fungi and viruses can infect it. Invertebrates are responsible for much of the post-dispersal seed predation. Spores of the fungus Ascochyta caulina applied as a mycoherbicide to fat-hen seedlings before the 4-leaf stage have been shown to cause up to 65% mortality. However, to be effective, moist conditions are needed for up to 24 hr after treatment. Necrosis and seedling death take up to 3 weeks to occur. Purified toxins from the fungus also have a phytotoxic effect on fat-hen.

Updated November 2007.

Fully referenced review: