Classification of weeds

Short-lived non-parasitic weeds

Short-lived non-parasitic weeds reproduce only by seeds, their lifespan is no more than 2 years, and they completely die off after seeds or fruits ripen. Depending on the duration of the life cycle, they are subdivided into: ephemerals, early spring, late spring, wintering, winter and biennial. The greatest number of weeds falls to the share of short-lived spring weeds.

Monocarpic weeds (monocyclic) — weeds fruiting once, with a one-year development cycle. Biennial ones have a two-year development cycle and are called dicyclic.

Ephemerals — plants with a very short growing season of 1.5–2 months. Capable of producing several generations during one season. Ephemerals include: common chickweed (Stellaria media), annual bluegrass (Poa annua), from the family Caryophyllaceae (Caryophyllaceae). They infest vegetable gardens, cereal crops and perennial grasses.

Early spring weeds show the properties of early spring crops: they begin growth early in spring at a soil temperature of 5–7 °C and finish development before or simultaneously with harvesting of cultivated plants.

These include wild oat (Avena fatua), white goosefoot (Chenopodium album), pale persicaria (Persicaria lapathifolia), corn spurry (Spergula arvensis), mustard field (Sinapis arvensis), darnel (Lolium temulentum), black-bindweed (Fallopia convolvulus), wild radish (Raphanus raphanistrum), large-flowered hemp-nettle (Galeopsis speciosa), common ragweed (Ambrosia artemisiifolia), wild hemp (Cannabis sativa var. ruderalis obsolete Cannabis ruderalis), crossflower (Chorispora tenella), in the north — roadside pepperweed (Lepidium ruderale). The latter is sometimes assigned to wintering weeds.

Late spring weeds show the properties 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 cultivated plants; in sowings of late crops — simultaneously with harvesting; in cereal sowings — in the post-harvest period. Autumn seedlings from shed seeds die from frost long before fruiting. They are mainly distributed in sowings of spring crops. Among them there are many specialized ones that grow only in sowings of crops similar in biological traits and agricultural practices.

Late spring weeds include: redroot pigweed (Amaranthus retroflexus), green foxtail (Setaria viridis), yellow foxtail (Setaria pumila), barnyardgrass (Echinochloa crus-galli), saltwort or kurai (Salsola), black nightshade (Solanum nigrum), common purslane (Portulaca oleracea), etc.

Wintering weeds finish vegetation with early spring seedlings in the same year, while with late seedlings they overwinter in any growth phase. After overwintering they form a rosette of basal leaves, a rapidly growing stem and finish vegetation early. This feature allows them to spread successfully in sowings of spring and winter crops. Spring seedlings do not form a basal leaf rosette, develop as spring ones, and ripen simultaneously with or somewhat later than harvesting of cereal crops. Seeds enter mainly into the soil, are very small, and retain germination capacity in the soil for up to 5–7 years.

Wintering weeds include: shepherd's purse (Capsella bursa-pastoris), field pennycress (Thlaspi arvense), scentless chamomile (Tripleurospermum inodorum), field larkspur (Delphinium consolida obsolete Consolida regalis), cornflower (Centaurea cyanus), flixweed (Descurainia sophia), Canadian horseweed (Erigeron canadensis), roadside pepperweed (Lepidium ruderale) (in the south), hedge mustard (Sisymbrium), corn cockle (Agrostemma githago). The latter is sometimes assigned to early spring weeds.

Winter weeds form shortened vegetative shoots in the first year and are in the tillering stage, develop a root system, accumulate nutrients, and form renewal buds on underground organs. After exposure to low temperatures, a short day in autumn and spring of the next year, they regrow and complete their full development cycle, forming seeds, and die off. The difference from wintering weeds is that they require low temperatures in autumn and winter. Regardless of the time of germination, they fruit only in the next year. They reproduce only by seeds. Seed germination capacity is retained from 2 to 4 years. Due to their biological properties, they are characteristic infestants of winter cereal crops, especially winter rye.

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

Biennial weeds pass through a full development cycle in two years. In the first year they form a leaf rosette and several stems in the lower tier. The root system goes deep into the soil. In spring of the next year the stem develops rapidly, and in summer the plant produces seeds. Typical biennials germinate in autumn and fruit only after 2 years, that is, after the second overwintering. Some weeds show the properties of winter crops: they germinate in autumn, develop as winter crops and produce seeds the next year. Annual forms are also found. Some species of biennial weeds, such as hill mustard (Bunias orientalis), do not die off after fruiting but produce shoots from the root collar or root segments.

Biennial weeds include: yellow sweet clover (Melilotus officinalis), white sweet clover (Melilotus albus), sickleweed (Falcaria vulgaris), black henbane (Hyoscyamus niger), bristly stickseed (Lappula squarrosa), hill mustard (Bunias orientalis), thistle (Carduus spp.), hemlock (Conium spp.), parsnip (Pastinaca spp.), campion (Silene spp.), hoary alyssum (Berteroa incana), etc.

Perennial non-parasitic weeds

Perennial non-parasitic weeds — plants with a growing period of several years, fruiting almost annually (semi-cyclic polycarpics). By methods of seed and vegetative reproduction they are subdivided into: rhizomatous, root-suckering, bulbous, tuberous, taprooted, fibrous-rooted and creeping.

Rhizomatous weeds reproduce mainly vegetatively by underground stems — rhizomes, which are distinguished by high viability and number of buds, from which new shoots and underground stems are formed. Due to this they spread quickly and over several years are capable of forming a dense sod. Seed reproduction is manifested unequally. One of the most widely represented groups of weeds. Control measures should first of all provide for destruction of vegetative organs — rhizomes. Depending on the depth of rhizome occurrence and biological features, different approaches are used to suppress their viability.

Representatives of the rhizomatous group: couch grass (Elytrigia repens), racemose wildrye (Leymus racemosus), branched wildrye (Leymus ramosus), Bermuda grass (Cynodon dactilon), Johnson grass or gumai (Sorghum halepense), field horsetail (Equisetum arvense), yarrow (Achillea millefolium), stinging nettle (Urtica dioica), coltsfoot (Tussilago farfara).

Root-suckering weeds reproduce by means of vertical and horizontal roots, on which a large number of dormant buds are located. From them root suckers (underground shoots) are formed in various directions and at various distances, developing into full-fledged aboveground shoots. Later these daughter shoots form an independent root system, lose connection with the mother plant and become centers of new vegetative reproduction. Gradually around the mother plant many independent plants appear, capable of occupying an area of several square meters. With further development individual patches turn into a continuous mass of weeds.

Weeds of this group, due to rapid spread and difficulty of destruction, are also considered noxious. They are distributed everywhere, occur in sowings of all field crops, develop on clean fallows, in gardens and vegetable gardens, and on fallow lands. Field sowthistle (Sonchus arvensis) and creeping thistle (Cirsium arvense) are more often found in the Non-Chernozem zone. In the forest-steppe and steppe zones on chernozem and chestnut soils, field sowthistle (Sonchus arvensis) and field bindweed (Convolvulus arvensis) are widespread. The twining stems of field bindweed often strongly entangle cereal crops, causing their lodging and a yield decrease of 30–50%. Sowings in the steppe arid regions of the southeast of Russia and in Siberia are often infested by Tartary lettuce (Lactuca tatarica), Russian knapweed (Rhaponticum repens), etc.

Horizontal roots in most weeds of this group are located within the arable layer. Root suckers have different, but generally high, ability to regrow. The most viable are reproductive roots and fragments of creeping thistle (Cirsium arvense), field sowthistle (Sonchus arvensis), Tartary lettuce (Lactuca tatarica); root segments of field bindweed (Convolvulus arvensis) are less viable and take root poorly. Unlike rhizomatous weeds, most root-suckering ones have high seed productivity, which complicates control methods. Seeds of some of them, such as field sowthistle (Sonchus arvensis) and sheep sorrel (Rumex acetosella), germinate immediately upon entering the soil; seeds of others (field bindweed (Convolvulus arvensis), Russian knapweed (Rhaponticum repens)) germinate more slowly. The optimal depth is 1–2 cm. Germination capacity is retained for several years.

The most widespread root-suckering weeds: field sowthistle (Sonchus arvensis), creeping thistle (Cirsium arvense), Tartary lettuce (Lactuca tatarica), Russian knapweed or pink knapweed (Rhaponticum repens), leafy spurge or rod-like spurge (Euphorbia virgata), field bindweed (Convolvulus arvensis), wintercress (Barbarea vulgaris), sheep sorrel or small sorrel (Rumex acetosella), common toadflax (Linaria vulgaris).

Tuberous weeds form thickenings on underground stems or roots, which germinate after overwintering and form a new plant. Capable of seed reproduction. Seeds germinate slowly and retain germination capacity for many years. They infest meadows and pasture lands. Tuberous weeds: marsh woundwort (Stachys palustris), purple nutsedge (Cyperus rotundus), etc.

Bulbous weeds reproduce by bulbils formed at the base of the mother bulb, as well as by seeds. Wild onions are distributed in the middle and southern parts of Russia in sowings of cereals and legumes, on virgin lands and meadows. Spread occurs when daughter bulbs separate from the mother bulb during soil cultivation. In autumn they germinate; after overwintering in spring they form a stem and inflorescence, on which seeds develop. In field garlic (Allium oleraceum), bulbils form in the inflorescence, because of which during harvesting of cereals they enter the grain. All types of weed onion reduce the quality of products and feed, giving them an unpleasant taste and smell. Bulbous: round-headed leek (Allium rotundum), field garlic or field onion (Allium oleraceum).

Creeping weeds reproduce vegetatively by means of stem shoots (runners, trailing shoots, etc.). They infest primarily meadows and pastures, especially in wet and low places; they are rarely found in fields.

Stem shoots, with the exception of ground-ivy (Glechoma hederacea), are annual. Shoots prostrate on the ground root at the nodes and form leaf rosettes, which after overwintering, in the next year, form independent weeds. The number of stem shoots from one plant can reach, under favorable conditions, 5–8, each up to 2 meters long. Reproduction by seeds, although of secondary importance, is strongly expressed. The preferred control method is proper soil cultivation, including stubble disking and fall plowing, as well as the use of herbicides.

Creeping weeds include creeping buttercup (Ranunculus repens), silverweed (Argentina anserina obsolete goose cinquefoil, Potentilla anserina), ground-ivy (Glechoma hederacea), etc.

Taprooted weeds have a tap main root capable of penetrating deep into the soil to 1.5–2.0 m in some species. They infest sowings of field and vegetable crops, and occur in gardens and meadows. In the Central Chernozem zone, wormwood (Artemisia absinthium) is widespread. In the south, in the central regions of the European part of Russia and in Siberia — chicory (Cichorium intybus). In the Non-Chernozem zone in sowings of perennial grasses, meadows, along roads and fallow lands — common sorrel (Rumex acetosa) and dandelion (Taraxacum officinale).

As a rule, they do not have special vegetative organs of reproduction; annually they form new shoots from adventitious buds in the lower part of the stem, drawn into the soil, as a result of which the main root shortens. New shoots and roots can form when the main root is cut or from its segment. In some species the main root can split lengthwise, giving rise to new plants and forming a dense bush. This phenomenon is called particulation. Taprooted weeds have limited ability for vegetative reproduction. The period of fruit (achene) germination is extended; achenes retain viability in the soil from 2 to 7 years. They germinate from a depth of no more than 5 cm, and only some species — from a depth of up to 7 cm (field scabious (Knautia arvensis)). Systematic soil cultivation, post-harvest stubble disking, fall plowing and cutting of emerging rosettes completely destroy taprooted weeds on arable land. In sown grasses, meadows and roadsides, systematic mowing and herbicides are used.

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

Fibrous-rooted weeds are represented by a small number of weed species having a fibrous root system and lacking special organs of vegetative reproduction. They occur in perennial grasses, on fallow lands, roadsides and ravines, in gardens and homesteads, sometimes in cereal sowings. They reproduce vegetatively from the root collar, less often by seeds. When the root collar is cut, they do not regrow. Fibrous-rooted include: meadow buttercup (Ranunculus acris), greater plantain (Plantago major).