Biological and ecological characteristics of weeds

Last updated: June 18, 2025

Over a long period, various species of weeds have acquired morphological and biological characteristics very similar to those of the crops in whose stands they most often grow, and this helps their spread.

Weeds compensate for the high rate of destruction by a number of characteristics:

less demanding of agroclimatic conditions, in particular more drought- and frost-resistant;
high seed productivity;
ability to reproduce vegetatively;
ability of seeds to spread over long distances by various means;
retention of seed viability over a long period;
extended period of weed seed germination;
high survival in various habitats.

An effective weed management system is impossible without a complete and comprehensive understanding of their biological characteristics. Knowledge of weed life characteristics makes it possible to determine growing periods in which they are least resistant to various agronomic practices or most sensitive to adverse external influences. This helps design a rational and economically justified system of preventive and eradication measures ensuring effective destruction of both vegetative weeds and their regenerative organs in the soil.

The biological similarity of weeds and crops explains their prevalence in crops: spring weeds in spring crops, winter and wintering weeds in winter cereal crops, etc.

Main features distinguishing weeds from crops:

Ability to reproduce vegetatively. Many perennial weeds reproduce rapidly by vegetative means. Their underground parts, producing many shoots with dormant buds, subsequently develop into independent plants.
Seeds of many weeds are able to retain viability for many years.
Uneven emergence of weed seedlings. This significantly complicates their control, since germination may be prolonged over a very long period. The non-uniform emergence of many weed species is explained by heterogeneity of seeds, which have unequal viability and different ability of the seed coat to let water through.

Seed productivity of weeds

Unlike crops, seed productivity of weeds is much higher, allowing them to maintain the population and mass spread, and also to mobilize for rapid mutation to changing environmental conditions and new agronomic practices, including herbicides.

Seed bank

In the arable soil layer of individual fields there are seeds of 10–25 different weed species, with their total number from 120 million to 3–4 billion per 1 ha. Such a potential reserve of weed seeds and fruits in the soil requires planned systemic control. This is one of the most important and promising tasks in agriculture.

Methods of spread of weed seeds and fruits

Methods of dissemination of seeds and fruits of weeds are divided into:

autochorous — spread by special devices driven by mechanical forces.
allochorous — with the help of various agents.

Autochorous spread can be:

autobaro chorous — spread of seeds under the action of gravity, shedding of seeds (field mustard (Sinapis arvensis), field cabbage (Brassica rapa subsp. oleifera, syn. Brassica campestris), wild radish (Raphanus raphanistrum), treacle mustard (Erysimum cheiranthoides), scentless mayweed (Tripleurospermum inodorum));
caused by tension in drying covering tissues of fruits (stork's bill (Erodium cicutarium), field pansy (Viola arvensis), narrow-leaved vetch (Vicia angustifolia));
by scattering seeds as a result of gusts of wind. For example, capsule-like fruits open when seeds ripen by teeth (corn cockle (Agrostemma githago), white campion (Silene latifolia), corn spurrey (Spergula arvensis)), pores (common poppy (Papaver rhoeas), creeping bellflower (Campanula rapunculoides)), a lid (black henbane (Hyoscyamus niger), pimpernel (Anagallis sp.)), etc.

Allochorous spread is divided into:

anemochorous — spread by wind (common dandelion (Taraxacum officinale), creeping thistle (Cirsium arvense), common groundsel (Senecio vulgaris), Canadian horseweed (Erigeron canadensis) and many others from the Asteraceae family. Thanks to feathery pappi, seeds are carried to surrounding fields and distant territories even in a weak wind over a distance of 2–5 km and more. Some weeds form a branching mass and acquire a spherical shape by the end of the growing season — "tumbleweed". Wind gusts break the dried stem at the base, and the plants get the opportunity to roll to other territories (Russian thistle (Salsola tragus), white amaranth (Amaranthus albus), flixweed (Descurainia sophia), narrow-leaved pepperwort (Lepidium ruderale), Psammophiliella muralis and others);
zoochorous — with the help of animals, birds, insects. For this, weeds have various adaptations — adhesive devices: anchors, hooks, serrated spines, bristles, awns, etc. Clinging to animal fur, bird feathers, human clothing, they are carried to other territories (Fig.). Fruits of field pansy (Viola arvensis), greater celandine (Chelidonium majus) can be spread by ants, which carry them to anthills and use them as food. A similar example is with seeds of wild hemp (Cannabis sativa var. ruderalis syn. Cannabis ruderalis) and firebugs (Pyrrhocoris apterus);
hydrochorous — dissemination with the help of spring and rainwater into lower parts of the relief. In this way, seeds of silky bentgrass (Apera spica-venti), field brome (Bromus arvensis), cornflower (Centaurea cyanus), field larkspur (Delphinium consolida syn. Consolida regalis), white goosefoot (Chenopodium album), toad rush (Juncus bufonius) are spread;
anthropochorous — spread as a result of everyday human agricultural activity. Insufficient cleaning of sowing material (grain, tubers and root crops insufficiently cleaned of soil, roots of seedlings and saplings). In this way, from southern regions of the country to the Non-Chernozem zone are periodically introduced blite amaranth (Amaranthus blitum), smallflower galinsoga (Galinsoga parviflora), common purslane (Portulaca oleracea), common ragweed (Ambrosia artemisiifolia), Russian knapweed (Rhaponticum repens) and others.

Fruits of weeds with pappi:
1 — creeping thistle (Cirsium arvense); 2 — common dandelion (Taraxacum officinale); 3 — common groundsel (Senecio vulgaris); 4 — eastern goat's-beard (Tragopogon orientalis).

Fruits of weeds with hooks:
1 — wild carrot (Daucus carota); 2 — stickseed (Lappula sp.); 3 — cleavers (Galium aparine); 4 — three-lobed beggarticks (Bidens tripartita); 5 — woolly burdock (Arctium tomentosum); 6 — common cocklebur (Xanthium strumarium).

Biological properties of seeds

Seed dormancy

Freshly shed seeds of weeds have a dormancy period, which can be natural (deep or physiological) and forced (secondary or ecological).

Natural dormancy is caused by:

incompleteness of physiological and biochemical processes (common cow parsnip (Heracleum sphondylium), cleavers (Galium aparine), shepherd's purse (Capsella sp.), four-seeded vetch (Vicia tetrasperma) and others);
presence of covering tissues impermeable to water and air (white melilot (Melilotus albus), pale persicaria (Persicaria lapathifolia), large-flowered hemp-nettle (Galeopsis speciosa), wild radish (Raphanus raphanistrum), annual woundwort (Stachys annua), field bindweed (Convolvulus arvensis), common viper's bugloss (Echium vulgare), Turkish rocket (Bunias orientalis), black-bindweed (Fallopia convolvulus) and others);
content in covering tissues of inhibitors that delay germination (white mustard (Sinapis alba), field mustard (Sinapis arvensis), field pansy (Viola arvensis), wild oat (Avena fatua), black henbane (Hyoscyamus niger), Canadian horseweed (Erigeron canadensis), common dandelion (Taraxacum officinale), common poppy (Papaver rhoeas), orange mullein (Verbascum phlomoides), greater plantain (Plantago major), black nightshade (Solanum nigrum) and others).

Forced dormancy is caused by the absence of favorable external life factors (lack of moisture, excess heat, absence of light, presence of plant inhibitors produced by other species, etc.). Seedlings of spring weeds appear in spring, plants bear fruit and die at the end of the growing season. Their seeds, as a rule, germinate only after overwintering. Seeds of early spring weeds germinate at soil temperature 2–4 °C, late ones — 12–14 °C and higher.

Weed seeds have an extended germination period, which significantly increases their survival as a species. The same is characteristic of seeds in the soil. This period can be stretched over several years: in the Non-Chernozem zone, seeds of cleavers (Galium aparine), redroot pigweed (Amaranthus retroflexus), creeping thistle (Cirsium arvense), field sow thistle (Sonchus arvensis) retain germination for two years, pale persicaria (Persicaria lapathifolia) and corn spurrey (Spergula arvensis) — 5–6 years, wild radish (Raphanus raphanistrum), black-bindweed (Fallopia convolvulus, syn. Polygonum convolvulus), common hemp-nettle (Galeopsis tetrahit), white goosefoot (Chenopodium album), field pennycress (Thlaspi arvense), common fumitory (Fumaria officinalis) — more than 10 years.

Longevity

Seeds of most crops retain viability under optimal storage conditions for no more than 4–7 years; seeds and fruits of weeds are able to retain viability after decades in the soil. An experiment started by W. Beal in 1879 at Michigan College, USA, showed the ability to germinate of seeds of common chickweed (Stellaria media), field mustard (Sinapis arvensis), shepherd's purse (Capsella bursa-pastoris), redroot pigweed (Amaranthus retroflexus), yellow sweet clover (Melilotus officinalis) after 30 years in the soil; seeds of field bindweed (Convolvulus arvensis), curly dock (Rumex crispus), black mustard (Mutarda nigra syn. Brassica nigra) — 50 years.

A measure for assessing the ability of weed seeds to retain viability is the ADR (Annual Rate of Decline) — annual rate of decline in seed viability in percent. Depending on the value of this indicator, weeds are divided into:

short-lived, ADR close to 100%, i.e., in the first few years in the soil, seeds completely lose the ability to germinate (brome (Bromus sp.), coltsfoot (Tussilago sp.));
transitional, ADR from 70 to 85% (annual grasses, some dicotyledons such as nipplewort (Lapsana sp.) and chamomile (Matricaria sp.));
moderately persistent, ADR about 50%, i.e., over several years half of the weed seeds lose viability (mainly dicotyledonous weeds: white goosefoot (Chenopodium album), field mustard (Sinapis arvensis), common poppy (Papaver rhoeas), toadflax (Linaria sp.), shepherd's purse (Capsella sp.), amaranth (Amaranthus sp.), knotgrass (Polygonum, syn. knotweed));
persistent, ADR about 10% (speedwell (Veronica sp.), chickweed (Stellaria sp.), pimpernel (Anagallis sp.)).

ADR values for some weeds: redroot pigweed (Amaranthus retroflexus) — 33%, wild oat (Avena fatua) — 83%, white goosefoot (Chenopodium album) — 37–48%, common poppy (Papaver rhoeas) — 35–54%, black nightshade (Solanum nigrum) — 35%, field mustard (Sinapis arvensis) — 34–43%, Italian ryegrass (Lolium multiflorum) — 75%, knotgrass (Polygonum aviculare) — 54%, spotted ladysthumb (Persicaria maculosa) — 32–40%, bristly foxtail (Setaria verticillata) — 75%.

Heterocarpy

Heterocarpy or heterocarpy — the property of some weed species to form in one inflorescence seeds and fruits with differing morphological and physiological characteristics. Heterocarpy increases establishment in new territories and adaptation to newly colonized agrocenoses.

Different time of fruit and seed maturation

During evolution, weeds acquired the property of completing their life cycle earlier than crops, which allows them to scatter seeds onto the soil before the optimal harvest time. For example, plants of wild radish (Raphanus raphanistrum), shepherd's purse (Capsella bursa-pastoris), field pennycress (Thlaspi arvense), annual knawel (Scleranthus annuus), red sandspurry (Spergularia rubra), growing in winter cereal crops, die one and a half to two weeks before threshing, due to which most seeds enter the soil. Seeds of scentless mayweed (Tripleurospermum inodorum), cornflower (Centaurea cyanus), field larkspur (Delphinium consolida), rye brome (Bromus secalinus), silky bentgrass (Apera spica-venti) also manage to shed their seeds several days before harvest.

In addition to early maturation of seeds, some weeds are characterized by unevenness of their maturation. Uneven shedding of wild oat grains, half of which mature by threshing time and manage to enter the soil (RIA of the Southeast).

Post-harvest weeds — weeds that form seeds and fruits after harvest. For example, in the steppe regions of Russia barnyardgrass (Echinochloa crus-galli), yellow foxtail (Setaria pumila syn. Setaria glauca), redroot pigweed (Amaranthus retroflexus), southern Russian thistle (Salsola australis), do not form seeds during the growing season of cereal crops. However, after threshing under favorable agroclimatic conditions, a short photoperiod, and optimal nutrient and water regimes in unplowed stubble, they rapidly complete their life cycle and after 2–3 weeks form an additional 40–60 million seeds per 1 ha.

Germination of seeds and fruits of weeds

Weed seeds have the property of regulating germination depending on external conditions. Freshly shed seeds have a low ability to germinate — no more than 3–8%. After a long stay in the soil, due to physiological ripening and increased permeability of covering tissues, which is observed after the autumn–winter period, germination of weed seeds significantly increases.

Decisive factors for seed germination are growth factors: moisture and heat. For example, for germination of seeds of green foxtail (Setaria viridis), barnyardgrass (Echinochloa crus-galli), redroot pigweed (Amaranthus retroflexus), annual woundwort (Stachys annua), soil moisture of 12–15% is required; for seeds of silky bentgrass (Apera spica-venti) — not less than 30%.

Requirements of weeds for the minimum soil temperature necessary for seed germination differ. Seeds of common chickweed (Stellaria media), wild radish (Raphanus raphanistrum), corn spurrey (Spergula arvensis), wild oat (Avena fatua), white goosefoot (Chenopodium album), field pennycress (Thlaspi arvense), scentless mayweed (Tripleurospermum inodorum) and others begin to germinate at soil temperature above 3–7 °C. Seeds of yellow foxtail (Setaria pumila), rice barnyardgrass (Echinochloa oryzoides), Amaranthus blitoides (Amaranthus blitoides), Russian thistle (Salsola tragus) and a number of other species growing in crops of late crops have a germination temperature above 18–20 °C.

Light, like other life factors, influences seed germination, accelerating their germination. The most light-sensitive are seeds of common purslane (Portulaca oleracea), perforate St John's wort (Hypericum perforatum), silky bentgrass (Apera spica-venti), curly dock (Rumex crispus) and others.

Most weed species have an extended period of seedling emergence, which can last throughout the growing season of crops, complicating their control in crops, especially during crop maturation.

The level of crop infestation is determined not so much by the viability of weed seeds as by the number of emerged seedlings. The optimal depth of germination of seeds and fruits of most weed species is no more than 5 cm. From a depth of up to 10 cm germinate seeds of Tatar buckwheat (Fagopyrum tataricum), mouse vetch (Vicia cracca), rye brome (Bromus secalinus), spiny cocklebur (Xanthium spinosum), annual sunflower (Helianthus annuus). Achenes of wild oat (Avena fatua) can germinate and form full seedlings from a depth of 20–25 cm. An increase in seed depth in the soil reduces their germination, and the resulting sprouts do not reach the surface and die.

Studies on the effect of seed storage depth on their viability, conducted by the Association for Agricultural Technical Coordination (<span lang="fr">Association de coordination technique agricole</span>, ACTA, France), showed different results after 2 and 4 years in the soil at depths of 2, 10, and 40 cm (graphs).

Depending on the ability of seeds to germinate from different depths, two limits were determined:

emergence limit — the maximum depth of weed seed placement from which they are able to germinate and produce seedlings;
germination limit — the maximum depth of seed placement at which weeds are able to germinate.

Emergence limit — the depth from which a plant is able to produce seedlings. Germination limit — the depth at which a plant is able to germinate, but if it is greater than the emergence limit, then seedlings will not appear on the surface. Below the emergence limit, seeds pass into a dormant phase — are preserved. Therefore, in weed control practice it is important to take this property into account.

There is an opinion that the germination limit is directly dependent on seed size.

For the use of weed seed properties, the following should be taken into account: periodic loosening of the arable layer promotes germination, including under arid conditions of the Volga region. Subsequent soil cultivation destroys emerged seedlings. On the contrary, placement of seeds into deep dense layers creates hypoxia (lack of air access), which leads to preservation of seeds for a longer time. Even once-shed weed seeds are able to provide seedlings for several years ahead.

Vegetative reproduction of perennial weeds

A feature of many weed species is the ability for vegetative reproduction from roots (rhizomes, bulbs, tubers), called reproductive roots. High ecological plasticity in this case is due to the quantitative abundance of roots or their parts and high regenerative ability for reproduction. The depth of occurrence of a significant part of such roots is not limited to the arable layer and can reach a depth of 1–2 m. This provides protection of weeds from destruction by tillage implements.

The ability for vegetative reproduction is due to the accumulation of plastic substances in roots mainly in the form of carbohydrates, the content of which, depending on the plant species and growing season, varies from 5–12 to 35–54%. On the roots there are a sufficient number of adventitious buds, which awaken when roots are damaged, and due to the reserve of plastic substances a new plant is formed.

Grinding of roots as a result of the action of tillage implements leads to the formation of a large number of fragments. Under favorable conditions, they take root and form independent plants. Weeds with high survival: field sow thistle (Sonchus arvensis), couch grass (Elytrigia repens), Tatar lettuce (Lactuca tatarica), field horsetail (Equisetum arvense). Low survival is characteristic of Russian knapweed (Rhaponticum repens), creeping thistle (Cirsium arvense), field bindweed (Convolvulus arvensis).

Due to a decrease in the amount of plastic substances with a decrease in the length of root segments, their regenerative ability also decreases. The smallest length at which regeneration is possible is observed in such weeds as field sow thistle (Sonchus arvensis), couch grass (Elytrigia repens) and some others capable of reproducing from segments 1–5 cm long. In addition, a decrease in the length of segments leads to awakening of a larger number of adventitious buds, resulting in a 1.5–2-fold increase in the regenerative ability of roots. Therefore, rare tillage in clean fallow or improper cultivation of inter-row spaces of row crops can lead to significant infestation.

In order to destroy weeds with a high ability for vegetative reproduction, roots are ground into small segments and placed to a depth of at least 20–25 cm. Due to limited plastic substances and great depth, the segments completely lose the ability to regenerate. This method of mechanical weed control is called the suffocation method.

An increase in soil density above 1.1 g/cm³, reduced moisture to 15–20%, and temperature below 5–10 °C sharply reduces the survival of root fragments. Thus, rhizomes of Bermuda grass (Cynodon dactylon) and Aleppo grass (Johnson grass, Sorghum halepense) completely die during the winter period in fields plowed for winter.

Perennial weeds have high ecological plasticity also in relation to unfavorable conditions. With severe mechanical damage to roots, excessive soil compaction, prolonged drought, the root system of Russian knapweed (Rhaponticum repens), creeping thistle (Cirsium arvense), field sow thistle (Sonchus arvensis), Tatar lettuce (Lactuca tatarica), field horsetail (Equisetum arvense) goes into a dormant state for 2–3 years. Their preserved root system renews regeneration with the onset of favorable conditions. This property explains in some cases the unexpectedly abundant appearance in plowed fields of perennial weeds previously not observed.

Weeds as indicators of habitat

The confinement of many weed species to certain field communities indicates not only their phytocoenotic compatibility with the crop, but also preferences for soil conditions of the habitat. In the latter case, the generalized reaction of weeds should be considered in two aspects: as indication of natural edaphic conditions and as their reaction to soil properties to some extent changed by agronomic measures in the process of human economic activity.

In relation to the level of soil moisture, the following groups of weeds are distinguished:

hygrophytes — occur almost exclusively on wet, poorly aerated soil (marsh cudweed (Gnaphalium uliginosum), toad rush (Juncus bufonius), silky bentgrass (Apera spica-venti), field horsetail (Equisetum arvense), field mint (Mentha arvensis), marsh woundwort (Stachys palustris), creeping buttercup (Ranunculus repens));
hygromesophytes — prefer sufficiently moist and well-aerated soils (white goosefoot (Chenopodium album), many-seeded goosefoot (Lipandra polysperma syn. Chenopodium polyspermum), common fumitory (Fumaria officinalis), cleavers (Galium aparine), scentless mayweed (Tripleurospermum inodorum), field pennycress (Thlaspi arvense), field sow thistle (Sonchus arvensis));
xerophytes — prefer well-aerated, warm, and at times strongly drying soils (redroot pigweed (Amaranthus retroflexus), Amaranthus blitoides, annual woundwort (Stachys annua), redstem stork's bill (Erodium cicutarium), bladder campion (Silene vulgaris), green foxtail (Setaria viridis), barnyardgrass (Echinochloa crus-galli), common ragweed (Ambrosia artemisiifolia)).

The use of this information is usually limited to taking into account the actual situation, whereas possibilities for regulating it are practically excluded.

By reaction to the value of pH (actual acidity), groups of weeds are distinguished:

oxalophytes — occur mainly on soils with pH < 5.0 (sheep sorrel (Rumex acetosella), corn spurrey (Spergula arvensis), annual knawel (Scleranthus annuus), corn spurrey (Spergula arvensis), scentless mayweed (Tripleurospermum inodorum), wild radish (Raphanus raphanistrum), silky bentgrass (Apera spica-venti), toad rush (Juncus bufonius));
oxalomesophytes — grow on soils with a soil solution reaction from slightly acidic to slightly neutral (wild oat (Avena fatua), spreading orache (Atriplex patula), treacle mustard (Erysimum cheiranthoides), field pennycress (Thlaspi arvense), black henbane (Hyoscyamus niger), marsh woundwort (Stachys palustris), silverweed (Argentina anserina syn. goose cinquefoil, Potentilla anserina), field sow thistle (Sonchus arvensis));
indifferent to soil solution reaction (white goosefoot (Chenopodium album), shepherd's purse (Capsella bursa-pastoris), corn cockle (Agrostemma githago), Canadian horseweed (Erigeron canadensis), large-flowered hemp-nettle (Galeopsis speciosa), common yarrow (Achillea millefolium)).

The presence of populations of several species from a specific group gives grounds for assessing the advisability of subsequent lime application to soils. This practice, often as a result of changing the floristic composition of weeds and improving crop development, sharply reduces crop infestation.

By the level of response to soil availability of mineral nutrients, "element-positive" and "element-negative" groups of weeds are usually distinguished. However, in agricultural practice it is important to know weeds that respond positively to high content of certain mineral nutrients in the soil.

The group of nitrophiles includes white goosefoot (Chenopodium album), many-seeded goosefoot (Lipandra polysperma syn. Chenopodium polyspermum), spreading orache (Atriplex patula), wild radish (Raphanus raphanistrum), field mustard (Sinapis arvensis), pale persicaria (Persicaria lapathifolia), large-flowered hemp-nettle (Galeopsis speciosa), bifid hemp-nettle (Galeopsis bifida), barnyardgrass (Echinochloa crus-galli), annual bluegrass (Poa annua), sheep sorrel (Rumex acetosella). As phosphate-loving weeds, the following should be distinguished: common groundsel (Senecio vulgaris), field pansy (Viola arvensis), corn spurrey (Spergula arvensis), red sandspurry (Spergularia rubra), common fumitory (Fumaria officinalis), henbit deadnettle (Lamium amplexicaule). From the group of potassium-loving weeds, it is necessary to name cleavers (Galium aparine), spreading orache (Atriplex patula), field pennycress (Thlaspi arvense), field sow thistle (Sonchus arvensis).

The given grouping of weeds by relation to various mineral nutrients is not strict, since with changes in mineral nutrition other life conditions usually change. As a result, the reaction of weeds to individual elements may also change. Nevertheless, this information, supplemented by other information of ecological and phytocoenological content, makes it possible to most rationally use lime materials and mineral fertilizers. At the same time, it is possible either to avoid increasing crop infestation or to develop measures in advance for more complete destruction of weeds.

Mimicry

Often populations of one weed species under different natural conditions behave as plants of different biological groups. Thus, field mustard (Sinapis arvensis) and corn cockle (Agrostemma githago) in the northwestern regions of Russia are typical early spring weeds, whereas in the southern regions they behave as wintering plants. Some weeds, for example, cornflower (Centaurea cyanus), scentless mayweed (Tripleurospermum inodorum), field pennycress (Thlaspi arvense), have both spring and wintering forms. Typical root-sprouting perennials field sow thistle (Sonchus arvensis) and field bindweed (Convolvulus arvensis) on overcompacted soils usually behave as taprooted weeds.

References

Bazdyrev G. I., Loshakov V. G., Puponin A. I. et al. (2000). Agriculture. Textbook for universities. Moscow: Kolos Publishing House.
Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of Agronomy: a textbook. Moscow: FORUM.
Niklyaev V. S. (2000). Fundamentals of agricultural production technology. Agriculture and crop production. Moscow: Bylina.