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Classification of weeds

Agrobiological classification of weeds of agrophytocenoses is used in the Russian practice of agriculture. It is based on the most important biological characteristics of weeds, taking into account the way of feeding, life span and method of reproduction.  Biological classification, based on morphological characteristics and, in contrast to the agrobiological classification, is of little use for building a system of weed control.

Agrobiological classification of weeds includes the following groups:

  1. Parasitic:
    • stem parasites;
    • root parasites.
  2. Semiparasitic:
    • stem semiparasites;
    • root semiparasites.
  3. Non-parasitic:
    • juveniles (annuals and biennials):
      • ephemerals;
      • spring early;
      • spring late;
      • wintering;
      • winters;
      • biennials.
    • perennials:
      • taproots;
      • root shoots;
      • creeping;
      • bulbous;
      • tuberous;
      • rhizomatous;
      • brush-rooted.

This classification was developed by L.I. Kazakevich, A.I. Maltsev, A.N. Fisyunov, S.A. Kott, etc.

The advantage of this classification is the association of weed species by biological characteristics with each other and with the type of weeded crops, which in production conditions allows you to use similar control schemes that have proven themselves before.

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Parasitic weeds

Parasitic weeds (heterotrophs) are weeds that have completely lost their ability to photosynthesize and provide themselves with water, minerals and organic matter by extracting them from the host plant.

Parasitic weeds use special sucking organs called gaustoria to extract nutrients from the host plant. Their leaves are reduced. Reproduction occurs by seeds, usually of very small size, distributed by wind and water, and capable of maintaining germination for 4-5 years. Depending on the place of their connection with the host plant, they are divided into root and stem ones.

Stem parasitic weeds

Stem parasitic weeds germinate from seeds in the soil. The young shoots of the parasite, devoid of leaves, wind around the host plant, using suction cups to penetrate its body and suck out water and nutrients, while losing contact with the soil.

Stem parasitic weeds include all species of Cuscuta: Cuscuta epithymum, Cuscuta europaea, Cuscuta epilinum.

Dodderweed (Cuscuta sp. sp.) is an annual plant with a curly, thin stem, with numerous suckers; it has scales instead of leaves, reproduces by seeds, and has no roots. Predominantly parasitizes on crops of clover, alfalfa, vetch, lentils, flax, hemp, and many weeds. Also infects some vegetable and cucurbitaceous crops.

The most common species of dodder are as follows.           

Cuscuta epithymum is a common species in the forest-steppe zone, a typical parasite of clover, alfalfa, and Hungarian sainfoin; it is sometimes found in flax, potato and other crops. Its seeds keep germinating in soil for 4-5 years; they are difficult to separate from clover seeds. They survive for more than a month in manure.

Cuscuta epilinum occurs in European Russia in flax-growing areas. It infects plants of flax, redroot, hemp, etc., as well as many weeds.

Cuscuta campestris occurs in the southern, southwestern and western parts of Russia. It parasitizes on clover, lentils, alfalfa, melilot, red and fodder beet, carrots, cucurbits and many weeds. It is the most aggressive and harmful species.

Root parasitic plants

Root parasitic weeds – about 100 species of Orobanche – annual plants that do not form green leaves, with very small seeds, easily spread by wind. Together with seeping water, they enter the soil and retain the ability to germinate for 5 years or more.

Hydrogen ions released by the root system of the host plant activate the growth processes of Orobanche seeds. Their sprouts penetrate deep into the root of the host plant, form suction cups there, and over them on the outside of the root – thickenings. A colorless fleshy stem (pedicel) grows from its upper part, and adventitious roots with suction cups emerge from its lower part. Up to 50 or more pedicels can grow on the roots of one host plant. Infested plant due to nutrient and water deficiency develops poorly or dies completely.

The following Orobanche species are most common in Russia.

Sunflower borer (Orobanche cumana) parasitizes mainly on roots of sunflower, tomato, tobacco, hemp and on some weeds. Widespread in areas where corresponding crops are cultivated, particularly in the Northern Caucasus, Middle Volga Region, and Lower Volga Region. Propagated by seeds which keep germinating until 6-7 years. One plant yields more than 100 thousand seeds.

Branched or hemp borer (Orobanche ramosa) may be found in such crops as tobacco, cabbage, pumpkin, melon, carrot, and sunflower. It also parasitizes weeds such as nettle (Urtica), wild hemp (Cannabis ruderalis), etc.

The Orobanche Aegyptiaca is considered one of the most dangerous Orobanche species; it infects over 90 plant species, including such cultural plants as cabbage, carrot, radish, potato, tomato, and melon. It is distributed in the south of European Russia.

Semiparasitic weeds

Semiparasitic weeds (hemiheterotrophs) are an intermediate class of weeds capable of photosynthesis and using water and nutrients of the host plant. In the absence of a host plant, they are able to develop their photosynthetic apparatus and root system. General and special measures are used for control.

They are subdivided into stem (white mistletoe (Viscum album), European stonecrop (Loranthus europaeus)) and root (big rattle (Rhinanthus alectorolophus), small rattle (Rhinanthus minor), narrow-leaved eyebright (Euphrasia ?) and small-flowered (Euphrasia micrantha), dentate late (Odontites ?) and common (Odontites vulgaris), field marianchis (Melampyrum arvense), bog myrtle (Pedicularis palustris).

Alecforolophus major is parasitic on the root system of winter rye and meadow grasses. Sprouts die after 6 weeks without rooting.  Germination of seeds remains for one year. Thorough cleaning of rye seeds during sowing with seeds of the previous year’s crop makes it possible to get rid of this weed.

Common bentgrass (Odontites rubra) is a common weed, parasitizing in northern areas on the root system of rye and cereal grasses, developing in the second half of summer; in steppe areas it appears on stubble and fallow lands.

Non-parasitic weeds

Non-parasitic weeds are a group of weeds capable of independent life activity. It is the most extensive group in terms of floristic composition. It is represented mainly by autotrophic plants. According to the prevailing method of reproduction and duration of life it is subdivided into juvenile and perennial.

Juvenile non-parasitic weed plants

Juvenile non-parasitic weeds reproduce only by seeds, their lifespan is not more than 2 years, they die off completely after the ripening of seeds or fruits. Depending on the duration of the life cycle, they are divided into: ephemera, spring early, spring late, wintering, winter and biennial. Spring weeds account for the greatest number of weeds.

Monocarpics (monocyclics (annuals)) are weeds that bear fruit once and have a one-year cycle of development. Biennials have a two-year cycle of development and are called dicyclics (biennials).

Ephemera

Ephemers are plants with a very short vegetation period of 1.5-2 months. They are capable of producing several generations during one season. Ephemerals include common chickweed (Stellaria media), annual bluegrass (Poa annua), and Caryophyllaceae. They infest vegetable gardens, crops of cereals and perennial grasses.

Common chickweed (Stellaria media) is a weed that grows quickly in low and humid places, on irrigated vegetable and well-cultivated plots. Stems are branched, almost creeping, 5-25 cm long, having adjoining nodes in the soil which are capable of producing adventitious roots. One plant gives 15-25 thousand seeds. Seeds are small, germinating from a depth of not more than 3 cm, keeping their germination for 2-5 years, overwintering if they develop too late.

Early spring

Spring early weeds show properties of early spring crops: they begin to grow in early spring at soil temperatures of 5-7°C and finish their development before or simultaneously with the harvesting of cultivated plants.

These are wild oat (Avena fatua), lamb’s-quarters (Chenopodium album), rough mountain worm (Polygonum scabrum), corn spurrey (Spergula arvensis), wild mustard (Sinapis arvensis), darnel (Lolium temulentum), wild buckwheat (Fallopia convolvulus), wild radish (Raphanus raphanistrum), Galeopsis speciosa, common ragweed (Ambrosia artemisiifolia), Cannabis ruderalis, blue or purple mustard (Chorispora tenella), Lepidium ruderale. The latter is sometimes referred to wintering weeds.

Late spring

Spring late weeds exhibit characteristics of late spring crops: they germinate in summer when the soil warms to 18-20°C, grow and develop slowly, ripening occurs after harvesting of early crops, in late crops simultaneously with harvesting, in grain crops in the post-harvesting period. Autumn sprouts of crumbling seeds die by frost long before fruiting.

Predominantly widespread in spring crops. Among them, there are many specialized weeds that grow only in the crops of crops similar in biological characteristics and farming techniques.

Late spring weeds include: redroot pigweed (Amaranthus retroflexus), green foxtail (Setaria viridis), blue broom (Setaria pumila), barnyard grass (Echinochloa crusgalli), saltwort or kurai (Salsola), black nightshade (Solanum nigrum), purslane (Portulaca oleracea) and others.

Wintering

Wintering weeds finish vegetation when early spring crops sprout in the same year, and with late sprouts they overwinter in any growth phase. After overwintering, they form a rosette of root leaves, a fast-growing stem, and finish vegetation early. This peculiarity allows successful spreading in spring and winter crops.

Spring sprouts do not form a root rosette of leaves, develop as spring crops, and mature simultaneously or somewhat later than harvested crops.

Seeds fall mainly into the soil, are very small and keep their germination in the soil up to 5-7 years.

Overwintering weeds include: Shepherd’s purse (Capsella bursa-pastoris), stinkweed (Thlaspi arvense), unflowered chamomile (Matricaria perforata), field larkspur (Consolida regalis), bachelor’s button (Centaurea cyanus), flixweed (Descurainia sophia), horseweed (Erigeron canadensis), Lepidium ruderale, Sisymbrium, purple cockle (Agrostemma githago). The latter is sometimes referred to early spring weeds.

Shepherd’s purse (Capsella bursa-pastoris) and stinkweed (Thlaspi arvense) due to their high ecological plasticity (have spring and wintering forms) infest crops of winter and spring cereals, row crops and forage grasses. They grow in fallow fields, along roadsides and fields, in gardens and orchards, in young fallows. Seeds of spring forms mature within 40-45 days after sprouting. May produce several generations within a year. Seeds are small, have a protracted germination period, and retain their germination for 6-7 years.

Bachelor’s button (Centaurea cyanus) infests winter and spring crops, and perennial grasses. Widespread in the Nonchernozem zone of Russia.

Unflowered chamomile (Matricaria perforata) infests grain crops, row crops and perennial grasses. May regrow after mowing. Widespread throughout the European part of Russia, Siberia and the Far East.

Winter

Winter weeds form short vegetative shoots in the first year and are in the tillering phase, develop a root system, accumulate nutrients, and form buds of regeneration on underground organs. After exposure to low temperatures and short daylight hours in autumn and spring of the next year, they grow and complete the full cycle of their development, forming seeds, and die off. The difference from wintering weeds is that they require lower temperatures in the fall and winter. Regardless of the time of germination, they do not bear fruit until the following year. Propagated only by seeds. Seeds germinate from 2 Bromus arvensis to 4 years Areca spica-venti.

Due to their biological properties, they are characteristic weeds of winter cereal crops, especially winter rye.

Representatives of winter weeds: rye brome (Bromus secalinus), field brome (Bromus arvensis) and common broom (Arega spica-venti).

Rye brome (Bromus secalinus) and field brome (Bromus arvensis) are contaminants of winter cereal crops, especially in excessively moist, poor and poorly cultivated fields. The seeds mature simultaneously with rye and become seeded, from which they are difficult to separate. Field brome has smaller seeds with a point, is less demanding of moisture, and is more common in the Central Black Earth zone. It germinates in the soil to a depth of 10 cm.

Common broom  (Arega spica-venti) has similar properties to bromegrass. Grows from a depth of no more than 5 cm. The seeds are very small and fall mostly into the soil and chaff.

Biennials

Biennial weeds undergo a full development cycle in two years. In the first year they form a rosette of leaves and a few stems in the lower tier. The root system goes deep into the soil.

In the spring of the following year, the stem develops quickly, and the plant produces seeds in the summer. Typical biennials germinate in autumn and bear fruit only in 2 years, i.e. after the second overwintering. Some weeds exhibit characteristics of winter crops: they germinate in autumn, develop as winter crops, and bear seeds the following year. There are also annual forms. Some biennial weeds, such as Bunias orientalis, do not die off after fruiting, but produce shoots from their root necks or root segments.

Biennial weeds include: Melilotus officinalis, white sweet clover (Melilotus albus), Falcaria vulgaris, black henbane (Hyoscyamus niger), Lappyla squarrosa, The bromegrass (Bunias orientalis), thistle (Carduus), hemlock (Conium), parsnip (Pastinaca), smolly (Silene), hoary alyssum (Berteroa incana), etc.

Melilotus officinalis is a drought-resistant plant that clogs crops of spring and winter crops, perennial grasses, edges of fields and roadsides. Widespread everywhere. The stem reaches 2.5 m in height. Seeds are covered with waterproof membrane and may survive for dozens of years in the soil. All parts of the plant contain poisonous alkaloids and glycosides. Feeding cattle causes poisoning of animals, gives milk an unpleasant taste.

Black henbane (Hyoscyamus niger) is a specialized contaminant of poppy crops. Its seeds and sprouts are similar in size and color to poppy seeds and are difficult to separate from them. Like the sweet clover, it contains poisonous alkaloids and glycosides.

Perennial non-parasitic weeds

Perennial non-parasitic weeds are plants with a vegetation period of several years, which bear fruit almost annually (semi-cyclic polycarpic plants). According to the methods of seed and vegetative propagation, they are subdivided into rhizomatous, root-shoots, bulbous, tuberous, taproots, fibrous-rooted (brush-rooted) and creeping.

Rhizomatous

Rhizomatous weeds propagate mainly vegetatively by underground stems – rhizomes, which are characterized by high vitality and the number of buds from which new shoots and underground stems are formed. Thanks to that, they spread rapidly, and in a few years can form a dense turf. Seed reproduction is manifested in different ways. One of the most widely represented groups of weeds.

Control measures should include, first of all, destruction of vegetative organs – rhizomes. Depending on the depth of the rhizomes and biological features use different approaches to suppress their viability.

Representatives of the group: couch grass (Elytrigia repens), branchy spikegrass (Leymus racemosus), waxwort (Leymus ramosus), Bermuda grass (Cynodon dactylon), johnsongrass (Sorghum halepense), field horsetail (Equisetum arvense), Achillea, Urtica, Tussilago.

Couch grass (Elytrigia repens) infests the crops of all cultivated plants. It is widespread everywhere except for arid areas where it yields to branchy wortle (Leymus racemosus). Root depth of Leymus racemosus is small, up to 90% of rhizomes are located at the depth to 12 cm. Its young rhizomes germinate at the beginning of summer and die off at the end of the following summer; those formed in autumn can live 15-16 months and overwinter twice. There is a peculiarity that the shorter is the length of rhizome pieces, the more buds are activated for growth. Therefore, increased shoot formation of crushed rhizomes is used to control it.

Bermuda grass (Cynodon dactylon) infests vegetable and field crops, orchards, vineyards and other lands. Widespread in southern regions of Russia, Transcaucasia, Ukraine, irrigated lands of Central Asia. Rhizomes are most viable at 2-3 years of age; they possess high adaptability, particularly at a young age; they may penetrate to a considerable depth during the growing season or come to the surface, dying off quickly in lack of moisture. Seed production is 2-3 thousand seeds, which do not detach from the plant for a long time.

Johnsongrass or humai (Sorghum halepense) infests crops of row crops, Sudan grass, and sorghum. Strongly oppresses alfalfa, winter vetch, and winter wheat crops. Widespread in the same areas as Bermuda grass. It has three types of rhizomes (A.I. Maltsev): primary (old), retaining viability and forming fruiting stems; secondary, growing from primary, short, emerging and producing new plants; tertiary (spare), growing from young plants. The main mass (up to 90%) of rhizomes is placed in the arable soil layer, but some offshoots are capable of penetrating 45 cm and deeper. Most of the seeds germinate after winter.

Field horsetail (Equisetum arvense) infests all crops, especially perennial grasses. It is widespread in sod-podzolic soils of the forest-meadow zone and in lowered damp places of the Central Black Earth zone. Rhizomes are located in the soil in several tiers at a depth of up to 45 cm. New shoots arising from adventitious buds grow from the thickenings (nodules) on the nodes of rhizomes. In autumn, buds are formed in the upper nodes of vertical rhizomes, from which spore-bearing and vegetative shoots emerge the next spring. This type of branching around the mother central shoot enables to create a wide network of rhizomes with above-ground shoots distant by a considerable distance. Old rhizomes, when cut or die off, form independent plants, due to which vegetative reproduction occurs. Viability of rhizomes is high; their segments in the presence of one viable bud take root and grow at depths of 30 cm or more. Spore-bearing shoots appearing in March or May produce a large number of spores, which do not play an essential role in reproduction.

Spikemoss (Leymus racemosus) infests all crops, being drought- and frost-resistant and therefore widespread in dry areas of Siberia and the steppe zone of the European part of Russia. Rhizomes lie 20-25 cm deep in loose soils, 15-20 cm or less in heavy soils. They occur horizontally, not reaching the soil surface, and have a strong pointed end that penetrates dense areas of soil, roots and tubers of other plants. Horizontal shoot-forming rhizomes of one plant can reach a length of 100 meters or more. After 3 years of vegetation, only weakly developed leaves form on vertical rhizomes, and in the fourth year the rhizomes die off. Sections of horizontal rhizomes less than 10 cm in length do not take root and die off quickly.

Root-shoots

Root shoots (root-sprouting) weeds reproduce with the help of vertical and horizontal roots, on which a large number of dormant buds are located. Root shoots (underground shoots) that develop into complete above-ground shoots are formed from them in different directions and distances. Later, these daughter shoots form an independent root system, lose connection with the mother plant and become foci of new vegetative reproduction. Gradually, many independent plants appear around the mother plant, capable of occupying an area of several square meters. Individual clumps further turn into a continuous mass of weeds. Weeds of this group due to rapid spreading and difficulty in destroying are also considered malignant.

They are widespread everywhere, occur in all field crops, developing on bare fallows, in orchards and vegetable gardens, in fallow. Perennial sow thistle (Sonchus arvensis) and Canada thistle (Cirsium arvense) are more often found in the Nonchernozem zone. Perennial sow thistle (Sonchus arvensis) and field bindweed (Convolvulus arvensis) are common in the forest-steppe and steppe zones on chernozem and chestnut soils. Curly stems of field bindweed often strongly entangle crops, causing their lodging and reducing the yield by 30-50%. Crops in the steppe arid regions of southeastern Russia and Siberia are often contaminated by Tartar lettuce (Lactuca tatarica), creeping mustard (Acroptilon repens), and others.

Horizontal roots of most weeds of this group are located within the arable layer: perennial sow thistle (Sonchus arvensis) and thrush (Euphorbia) at a depth of 5-15 cm, and Canada thistle (Cirsium arvense) and creeping mustard (Acroptilon repens) at a depth of 25-30 cm. Part of root scions of Tartar lettuce (Lactuca tatarica) and field bindweed (Convolvulus arvensis) are located below the arable layer.

Root shoots have different, but generally high, regrowth capacity. The most viable propagules and debris are roots of Canada thistle (Cirsium arvense), perennial sow thistle (Sonchus arvensis), Tatar lettuce (Lactuca tatarica), etc. Root fragments of field bindweed (Convolvulus arvensis) are less viable and do not take root.

Unlike rhizomatous weeds, most root-shoots weeds have high seed production, which complicates control measures. Seeds of some of them, such as perennial sow thistle (Sonchus arvensis) and small sorrel (Rumex acetosella) germinate immediately upon entering the soil, seeds of others (field bindweed (Convolvulus arvensis), creeping mustard (Acroptilon repens)) germinate more slowly. Optimal depth of 1-2 cm. Germination lasts several years.

The most common root weeds: perennial sow thistle (Sonchus arvensis), Canada thistle (Cirsium arvense), tartar lettuce (Lactuca tatarica), creeping or pink mustard (Acroptilon repens), burdock or bar grass (Euphorbia villosa), field bindweed (Convolvulus arvensis), yellow rocket (Barbarea vulgaris), sparrow sorrel or small sorrel (Rumex acetosella), toadflax (Linaria vulgaris).

Bulbous and tuberous

Tuberous weeds form thickenings on underground stems or roots that germinate after overwintering and form a new plant. They are capable of seed reproduction. Seeds germinate slowly and retain germination for many years. Widespread in meadows and pastures.

Bulbous weeds reproduce by bulbs formed at the base of the parent bulb and by seeds. Wild onions are common in the middle and southern parts of Russia in crops of cereals and legumes, in virgin lands and meadows. Spreading occurs when daughter bulbs are separated from their mother bulbs during tillage. They sprout in the fall and, after overwintering in the spring, form a stem and inflorescence on which seeds develop. Onions of the vegetable onion (Allium oleraceum) form their bulbs in the inflorescence, which causes them to enter the grain during harvesting. All types of weeded onions reduce the quality of products and fodder, giving them an unpleasant taste and odor.

Tuberous weeds: marsh peaweed (Stachus palustris), purple nutsedge (Cyperus rotundus), etc.

Bulbous weeds: round onion (Allium rotundum), garden or field onion (Allium oleraceum).

Creeping

Creeping weeds reproduce vegetatively by means of stem shoots (whiskers, stems, etc.). They primarily infest meadows and pastures, especially in damp and low-lying places; they are rarely found in fields. 

Stem shoots are annual, except for ground ivy (Glechoma hederacea). Cauline shoots grow on the ground, root at their nodes and form rosette of leaves which form independent weeds after overwintering in the next year. Under favorable conditions the number of stem shoots of one plant can reach 5-8, up to 2 meters long each. Propagation by seeds, though of secondary importance, is strongly expressed.

Proper tillage, including removing stubble and autumn plowing, as well as the use of herbicides are the preferred method of control.

Creeping weeds include creeping buttercup (Ranunculus repens), goosefoot (Potentilla anserina), ground ivy (Glechoma hederacea), etc.

Taproots

Taproot weeds have a tap root capable of penetrating deep into the soil up to 1.5-2.0 m in some species. They infest crops of field and vegetable crops and occur in gardens and meadows. Absinthe (Artemisia absinthium) is widespread in the Central Black Earth zone. In the south and in the central areas of the European part of Russia and in Siberia – chicory (Cichorium intybus). In the Non-Black Soil Zone in perennial grasses, meadows, roads and bogs – sour sorrel (Rumex acetosa) and dandelion (Taraxacum).

As a rule, they have no special vegetative organs of reproduction, annually forming new shoots from adventitious buds in the lower part of stems retracted into the soil, resulting in shortening of the main root. New shoots and roots may be formed by pruning the main root or from a section of it. In some species, the main root may split lengthwise, giving rise to new plants and forming a dense bush. This phenomenon is called particulation.

Taproot weeds have limited ability to propagate vegetatively. The germination period of fruits (seeds) is elongated; seeds keep their vitality in soil from 2 to 7 years. They germinate from a depth of not more than 5 cm and only some species germinate from a depth of up to 7 cm (Knautia).

Systematic tillage, post-harvesting of stubble, autumn plowing and pruning of rosettes that have emerged completely eliminate rod-root weeds in the arable land. Systematic mowing and herbicides are used in seeded grasses, meadows, and roadsides.

Examples: absinthe (Artemisia absinthium), chicory (Cichorium intybus), field scabious (Knautia arvensis), sour sorrel (Rumex acetosa), horse sorrel or dense sorrel (Rumex confertus), medicinal dandelion (Taraxacum officinale), common smolt (Silene vulgaris), tall larkspur (Delphinium elatum), etc.

Fibrous-rooted (brush-rooted)

Fibrous-rooted (brush-rooted) weeds are represented by a small number of weed species with a fibrous root system and lacking special organs for vegetative propagation. They are found in perennial grasses, in backyards, roadsides and ravines, in gardens and homesteads, sometimes in grain crops. Propagated vegetatively from the root neck, less often by seeds. When the root neck is pruned, they do not regrow.

The Brush-rooted (fibrous-rooted) weeds include: buttercup (Ranunculus acris), plantain (Plantago major).

Specialized weeds

Specialized weeds are weeds characteristic of one crop or species of cultivated plants. In the course of evolution, specialized weeds have acquired biological and morphological traits similar to the crop they infest. Examples of such traits: the time of emergence of seedlings, the duration of the life cycle, rhythmic of development, height, shape of inflorescence, habitus, leaves, coloring, etc.

The emergence of specialized weeds is also closely related to the similarity of seeds and fruits in physical and mechanical features: shape, size, mass, and sailing. As a result, seed cleaning is complicated, and weed seeds get into the seed material of the crop. Such weeds are also called difficult to separate.

Examples of specialized weed plants are:

  • rye brome (Bromus secalinus) and field brome (Bromus arvensis) in winter rye;
  • Sophora alopecuroides, Cephalaria syriaca, common dayflower (Commelina communis), tartary buckwheat (Fagopyrum tataricum) in wheat;
  • wild oat (Avena fatua), bristle oats (Avena strigosa) in oat and barley crops;
  • tartary buckwheat (Fagopyrum tataricum) in buckwheat crops;
  • flax thistle (Spergula alyssum), Camelina alyssum, Lolium remotum, Johnsongrass (Sorghum halepense), Rhaponticum repens in fiber flax crops;
  • barnyard grass (Echinochloa crus-galli) in millet crops;
  • common pearl millet (Echinochloa oryzoides), and barnyard grass (Echinochloa crus-galli) on rice crops.

Most of the weeds of this group do not occur in the crops of other crops, because the infestation occurs simultaneously with the seed material of a characteristic (specific) crop.

Quarantine weeds

Quarantine weed plants – a group of particularly harmful, absent or limited distribution of weeds in the territory of the country or a particular region. Governments of different countries establish lists of quarantine weeds in their territories. In Russia, the list of quarantine objects was approved by Order of the Ministry of Agriculture of Russia № 501 of December 15, 2014, according to which the following species are classified as quarantine weeds:

  1. Absent in the territory of the Russian Federation:
    • Elderberry or willow perennial (Iva axillaris);
    • Ipomea hederacea (Ipomoea hederacea);
    • Ipomoea lacunosa (Ipomoea lacunosa);
    • Passerine leafy (Solarium elaeagnifolium);
    • Carolina nightshade (Solarium carolinense);
    • Ciliate sunflower (Helianthus ciliaris);
    • Striga (all species) (Striga);
    • Bidens pilosa (Bidens pilosa) – included in the new list;
    • Bipinnata (Bidens bipinnata) – included in the new list.
  2. Limitedly distributed in the territory of the Russian Federation:
    • Common ragweed (Ambrosia artemisiifolia);
    • Great ragweed (Ambrosia trifida);
    • Ambrosia perennialis (Ambrosia psilostachya);
    • Creeping (pink) gentian (Acroptilon repens);
    • Spiny (beak-shaped) nightshade (Solarium rostratum);
    • Tricolor nightshade (Solarium triflorum);
    • Dodders (all species) (Cuscuta);
    • Cenchrus longispinus (Hack) Fern – newly listed.
  3. Regulated non-quarantine plants:
    • Ailanthus altissima, Chinese ash (Ailanthus altissima (Mill.) Swingle).

Previously listed, currently absent:

  • Cenchrus pauciflorus (Anchorwort) (Cenchrus pauciflorus);
  • California sunflower (Helianthus californicus).

Classification of weeds in foreign farming practices

In foreign farming practice, as a rule, a more simplified classification of weeds is used:

  • Annual – vegetation period is 1 year, they reproduce by seeds, vegetative reproduction is weak or absent. Example: cleavers (Galium aparine).
  • Biennial – vegetation period is 2 years, they propagate by seeds mainly, vegetative propagation is weakly expressed. Example: wild carrot (Daucus carota).
  • Perennials – the vegetation period is several years, they reproduce both by seeds and vegetatively (the latter to a lesser extent). Example: curly sorrel (Rumex crispus).
  • Eternal – the vegetation period is unlimited, they reproduce both by seed and vegetatively (the former to a lesser extent). Example: Canada thistle (Cirsium arvense).

Sources

Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.

Fundamentals of agronomy: textbook / Yu.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.

Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. — Moscow: Bylina, 2000. — 555 с.

Bazdyrev G.I. Weed plants and measures to control them in modern agriculture: Textbook for universities. M.: Publishing house of the Moscow Agricultural Academy, 1993. – с. 242.

Éléments de biologie des mauvaises herbes – Les leviers de gestion de la flore adventice, Agri-Réseau (translated from French by UniversityAgro.ru)