Weed

As weeds ( in Switzerland weeders ) is called spontaneous plants of understorey vegetation in crops of cultivated plants, grassland or gardens that are not there purposely grown and come from the seed potential of the soil or Zuflug to development. In common parlance, is the main criteria to designate a plant as a weed, that it is undesirable. Depending on the perspective of the person concerned may be an already occurred to fear Direction economic loss or aesthetic reason, the trigger for the disorder feeling. These may be undesired wild plants or crop plants spontaneously growing up. The term is not limited to herbs in the true sense, but also includes grasses, ferns, moss or woody plants. In the field of plant protection, the term weed is often used to illustrate a distinction to the herbaceous plants.

Definition

The interpretation of the term weed depends heavily on the subjective human perception. For example, some plant species are referred to as a lump sum weed. This is the basic principle according to false, since the same type can occur as weeds, crop, herb, plant pointer or in some other form. For weed it is only in this way that it is perceived as " disturbing ". Different views on here often lead to disputes between neighbors, sometimes even political debates. It does not matter whether it is a herbaceous or woody plant species in a " weed " in the second case, one could also use the term " Unholz ".

As part of the environmental movement in the 1980s was called on to replace the term " weed " with " weed ". " Weed " is, however, already used for the description of wild edible herbaceous plants so that this demand could not prevail. Alternatively, it is now often spoken of Beikraut or crop companions, when in the actual sense unwanted plants (ie weeds ) are meant. In forestry, the term ancillary growth is common, since both negative and positive side effects can be expected.

Plants are usually referred to as a weed if they:

  • Occur at a specific crop grown in competition for growth factors such as nutrients, light, water, so that the crop does not reach the desired yield;
  • The management of a difficult area by fall, for example, in the crop and contaminate it;
  • A mass distribution have is ( by seed flight, extremely long root systems, displacement of competitors ) and thus the risk that they settle on surfaces to be protected;
  • The aesthetic sense of a man interfere, for example in ornamental gardens, parks, lawns or vegetation to be kept free surfaces;
  • By their toxic effects make the income of an area unusable ( eg autumn crocus in hay).

Herbology

The field of weeds customer has evolved in recent decades under the name herbology to an independent scientific discipline. The department deals with issues of weed biology, weed ecology and weed control and the resulting impact on the environment.

Arable weeds

Weed of agriculture creates problems naturally. The weed populations on a farmland are affected by factors such as crop rotation, type of tillage, mechanical maintenance and other measures. General common today is the use of weed killers ( herbicides ), are threatened by the many arable weeds in their inventory.

Organic farming has a more nuanced perspective on the " weeds " that they see not only as a harmful plant, but also as an essential part of the ecosystem. Therefore, there is the negative occupied term " weed " and rejected the neutral name Beikraut preferred. The scientific name of this group of plants is Segetalpflanzen.

History

The problem of weeds is as old as agriculture itself In the Bible it is mentioned as God's punishment for the Fall. So is the 1st book of Genesis (Chapter 3, 17-18): " ... cursed is the ground for thy sake, in sorrow shalt thou feed on your life. Thorns and thistles shall it bring forth to thee ... ".

In Central Europe, agriculture has been operated since the Neolithic period, the cleared areas were small. With the scratch plow not turning over the entire field surface was possible between the plow furrows the weed vegetation was hardly disturbed. The fields were heavily interspersed with ruderal and pasture plants. During archaeological investigations it was found that the species composition of the Neolithic period ( about 4000 BC) to the Bronze Age ( about 1250 BC) essentially stayed the same ( with decreasing frequency: lambsquarters, Polygonum convolvulus, Common Rain cabbage, Dove brome, Kletten-Labkraut/Kleinfrüchtiges K., sorrel species, Phleum nodosum cf, ordinary bluegrass, flea knotweed and various vetches ).

In the Roman era, many weed species that are now typical of grain fields were introduced with seed from the Mediterranean countries.

During the Middle Ages most of the fields according to the principle of the three-field system were ( - summer corn - winter wheat fallow) ordered. During the fallow, the cattle were driven to the fields. Even the young grain stocks were grazed what they damaged only slightly. The weed was more suppressed than the corn which only gets stronger by the area under grazing. A selective weed control was carried out by weeding, the weeds stocks contained many pasture plants.

In the 18th century came the improved crop rotation ( winter wheat - summer corn - root crops) on. It emerged the typical hack - and Halmfruchtunkrautfluren.

Utility of weeds

Weeds promote good tilth by roots by the soil between the crops and protect from direct sunlight. Stay on fields that have long without vegetation (eg corn ) they can counteract erosion. The same is true for vineyards - here allows growth with low plants in some cases only the driving.

Wild plants are an important gene reservoir, which should also be maintained in view of a possible future use. Some crops, such as the culture of the turnip, corn salad or rye were originally weeds. A number of weeds are important medicinal plants, such as chamomile, plantain, and horsetail.

In the context of biological control, they enable parasitic wasps, caterpillars, flies and other beneficial insects to survive in the field, as long as no infested crops are available.

Belonging to plant families (selection)

In Europe, about 650 species of plants can be counted among the arable weeds. Half of this belongs to the family of Asteraceae, Brassicaceae, Caryophyllaceae and Poaceae. These families are very rich in species outside the weed societies. What is striking is the rather disproportionate share of goosefoot, pigweed and buckwheat family.

Weeds are usually "seed weeds " with a short generation time and partly several generations per year. The number of seeds per plant can be extremely high, the ordinary shepherd's purse can develop 90,000 seeds a vigorous plant. Where weed seeds a few inches into the ground, for example by plowing, he or she can survive for many years. One speaks in this context of the seed bank of the soil.

Duration weeds are perennial plants that can regenerate quickly from their roots or rhizomes. These include, for example, creeping thistle, field bindweed, couch grass, some sorrel species and horsetail. These types can even be promoted by not carried out correctly Mechanical control, as they re- sprout even from root and Rhizomfragmenten.

In the Central European forestry include, for example, the bird cherry (Prunus padus ) or black locust (Robinia pseudoacacia) to the " unloved " plant species, ie " Unhölzern ".

Weed societies

The composition of the weed stocks on the fields is dependent on a number of factors. Even more important than the particular crop is the last time that "radical" cultural action, whether through hacking, plowing, harrowing, steaming or using a herbicide.

If the last tillage in late autumn or early spring happens creates a cereal weeds society, even when no grain is grown on the field this year. If this last measure culture until May or June, a so-called weed Society forms. This is due to different dormancy and germination temperatures of the weed seeds.

The properties of the soil also have an effect on the weeds stocks. Of particular importance are the effects of soil reaction, nutrient and water supply and soil type. The climate and the existing seed bank at each location are important.

The weeds companies were in the phytosociological classification during the last 80 years regrouped again and again, for example by Braun- Blanquet 1936 or Oberdorfer 1957. The last major reorganization in 1990 by Hüppe and Hofmeister.

Conservation aspects

In Germany, one-third of the approximately 270 species of plants which have their main occurrence in the weed - and short-lived ruderal vegetation is considered as regionally endangered or extinct. The conservation of these species by maintaining the traditional farming system would be very expensive. Their preservation in the Botanical Gardens is difficult because it almost inevitably plants are read, where important ( weed ) properties are missing, such as the germ default.

With great success, field margins programs were introduced in the 1980s in several states. Here, farmers undertake in return for compensation, not to treat the edges of fields with pesticides. In many states, the interest in the field margins programs has decreased markedly over the 1990s until today. The documented in the Red Lists hazardous situation for the Segetalflora has not improved ( detailed description in Karl townspeople position paper). For this reason, in 2007, the nationwide protection arable project called " 100 fields for diversity" to life.

In addition to the plants themselves also different groups of animals by the decline of the weeds are concerned, because these animals feed partly or completely of pollen, nectar, stems and leaves, roots or seeds of weeds or use the weeds as habitat. The reduced availability of weed seeds has so in recent decades among others to a sharp decline of granivoren ( seed -eating ) birds of the agricultural landscape with contributed.

Types Overview

The table below is the simplified version of a similar table in Wilmann (1993). You will gain an initial overview, which occur plant species on which arable land.

Modern weeds

In addition to the "classic weed " prepare "modern weeds " as invading plants ( neophytes ) by rapid spread of agriculture, forestry and nature conservation sometimes serious problems. Firstly, they are - rather unintentionally - was introduced by the modern mobility ( such as the giant hogweed ), on the other planned imports about to limited greening purposes, they could no longer be contained in their dissemination (for example, flowering quince, vinegar tree, Himalayan balsam or black cherry ).

Usage

Weeds are often removed mechanically by hand. The German language knows for various terms: weed, pluck, ruppsen, rupschen, pull, pluck.

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