Weed seed germination lambsquarter

Lambsquarters, common

Description: Seedlings have thumb- to long ellipse-shaped, 0.16–0.6 inch long by 0.04 inch wide cotyledons. Upper sides of cotyledons are dull green; seedling stems and undersides of cotyledons are maroon-green. The first two leaves are egg shaped and opposite; all subsequent leaves are alternate, although the first few leaves may appear opposite. Young leaves have a silvery or pink, grainy or mealy coating. The diamond-to-egg-shaped young leaves arise from a silvery to light green, mealy stem; leaf edges are either entirely or lightly toothed. Stems of mature plants are upright, pyramidal, highly branching, hairless, ridged, maroon-speckled and can reach 3–5 feet tall. Leaves are alternate, 1.2–4 inches long by less than 3.5 inches wide, green, and diamond or egg to triangle shaped, with mealy undersides. Lower leaves are broader, longer and usually toothed and stalked. Upper leaves are sometimes lanceolate, stalkless and toothless. The taproot is short and branched. Individual flowers are very small, inconspicuous and silvery to green; they are clumped together in dense clusters located in stem-leaf junctions and at branch tips. Seeds are round, black and 0.06 inch wide, or they can be brown and slightly larger with a flatter oval shape. Papery flower tissue closely coats most of the seed surface at dispersal.

Similar species: Halberdleaf orach (Atriplex patula L.) is similar to common lambsquarters and has a white mealy bloom on young growth. Halberdleaf orach is shorter and bushier than common lambsquarters, and its leaves are generally more lanceolate, less toothed and often have a pair of narrow lobes near the base of the leaf blade. Common lambsquarters seedlings are sometimes confused with several young pigweed species (Amaranthus spp.). Young, true leaves of common lambsquarters seedlings have a grainy or fuzzy, silver to pink bloom when they first emerge, but pigweed seedlings do not. Mature common lambsquarters leaves generally have toothed, sculpted edges while pigweeds have generally oval shaped, untoothed leaves. Other Chenopodium spp. do not have mealy young tissues, diamond- to egg-shaped leaves and light colored, succulent looking stems.

Management

Common lambsquarters germinates readily in response to tillage and cultivation. More than most weed species, a one- to two-week lag between initial and final seedbed preparation is effective at flushing out and destroying seedlings. A short fallow in the spring with repeated surface cultivation causes even greater depletion of the surface seed bank. The key is to use progressively shallower tillage, with the final seedbed prepared to a depth of no more than 1.5 inch. The species rarely emerges from deeper than that, and deeper tillage will raise seeds into the near-surface zone favorable for germination. Continue killing seedlings after crop planting by tine weeding with blind cultivation. Once the crop is large enough to tolerate inter-row cultivation, hill up slightly when the lambsquarters seedlings are still in the early seed-leaf stage. Even crops like cabbage and tomatoes that are not normally hilled will tolerate 1 inch of soil against the base, and this is sufficient to bury the tiny seedlings. Continue hilling with subsequent cultivations if the crop will tolerate it.

In spring and fall planted grains, a dense, uniform and vigorous stand is critical for maximizing the crop’s initial competitive advantage. Light harrowing just as the lambsquarters seedlings begin to emerge can substantially reduce density of the weed, but any substantial reduction in stand density of the grain is likely to prove counterproductive.

Straw mulch and other mulch materials are highly effective for suppressing this species since its small seeds provide few resources for pushing the seed leaves up out of the mulch mat. Because the seed leaves stay together in a vertical position until they reach the light, however, a few seedlings will usually penetrate at least 2 inches of loose straw, so either use a deeper mulch layer or compact the mulch after application.

Common lambsquarters is highly responsive to N fertility. Avoid excess fertilization, and, in particular, avoid heavy fertilization before the crop is well established. On the other hand, incorporation of a legume cover crop can enhance seed bank decline of this species by triggering fatal germination of buried seeds.

Because common lambsquarters is a prolific producer of long-lived seeds, consistent efforts to limit seed production will greatly assist long-term management. Since most seeds remain on the plant long after they mature, they can be captured or destroyed during combine harvest. Clean up fields promptly after harvest if this weed is present. If possible, remove plants that have flowered, as they can continue to form seeds even after mowing or light tillage that leaves the flowering stalks on the soil surface. Hand rogue at least the larger plants out of intensive vegetable systems. Many of the seeds remain on the plant until early winter, so fall cleanup after harvest can reduce lambsquarters density the following year. In a long-term vegetable crop rotation, seed banks of common lambsquarters tended to decrease with deep plowing to 14–16 inches but increased with rotary tillage or shallow plowing to 6–7 inches. Despite the potential longevity of common lambsquarters seed banks, the species can be virtually eliminated from a field through proper crop rotation coupled with other good management practices.

Ecology

Origin and distribution: Common lambsquarters was introduced from Europe. It is present in all 50 states and in all Canadian provinces and territories except for Nunavut. It has been introduced throughout the world and is widespread from 70° N to 50° S except in extreme deserts.

Seed weight: 0.5–0.7 mg depending on the population and type of seed; the same plant may produce several types of seeds with different size and dormancy characteristics.

Dormancy and germination: Common lambsquarters frequently produces two or more visually distinct types of seeds on the same plant, and these differ in their dormancy properties. Many seeds are usually dormant immediately after falling from the parent plant, but some are not. A period of cold, wet conditions breaks dormancy, and warm weather in early spring promotes subsequent emergence. Seeds produced under short day-length conditions are less dormant than those produced during long days. Common lambsquarters germination is substantially increased by white light but is inhibited by light depleted in red wavelengths, such as light that has passed through a plant leaf canopy. Germination is increased by the presence of nitrate and by large day/night temperature fluctuations. The germination promoting effects of light, nitrate and fluctuating temperature act together such that more seeds germinate with two of these cues than with one, and maximum germination is usually reached when the seeds receive all three cues. All of these cues tend to occur during or shortly after tillage. Seeds from plants grown in high nitrate conditions have higher N concentrations and higher germination rates than seeds from unfertilized soil. Seeds germinate best with daytime temperatures of 64–77°F. The process of germination begins at temperatures as low as 43°F, but relatively few seeds germinate below 55°F or above 91°F. A few weeks of exposure to temperatures over 59°F causes some seeds to enter secondary dormancy, and thus, warm weather in summer induces dormancy in a substantial fraction of seeds.

Seed longevity: Common lambsquarters seeds can remain viable in the soil for many decades. As an extreme example, viable seeds have been recovered from under medieval ruins in Europe. Most seeds, however, do not last so long. In undisturbed soil, mortality rates of 8–35% per year have been observed, with most rates near the lower end of the range. In New York, annual seed mortality was variable, with a more typical average rate of 21% in one experiment but an unusually high rate of 78% in another. In long-term conventional and organic plots in the mid-Atlantic states, annual seed mortality averaged 51%. In annually tilled fields, decline in the common lambsquarters seed bank has varied from 14–42% per year, with most loss rates nearer the higher value. In soil stirred six or more times per year, seed loss was 31–52% per year.

Season of emergence: Common lambsquarters emerges throughout the growing season but with a strong peak in spring. It is categorized as an early emerging species that begins emergence in early spring, but it has one of the longest emergence durations of all weeds studied.

Emergence depth: Optimum depth for emergence is near the soil surface, 0.1–0.2 inch, and few seedlings emerge from deeper than 1.2 inch.

Photosynthetic pathway: C3

Sensitivity to frost: Common lambsquarters is sensitive to frost.

Drought tolerance: The species is relatively drought tolerant.

Mycorrhiza: The species is non-mycorrhizal.

Response to fertility: Common lambsquarters is a heavy feeder of plant nutrients. It has a strong growth response to increasing N applications up to at least 480 pounds per acre and a moderate response to P up to about 46 pounds per acre of P2O5. Plants grew substantially larger with 5,830 pounds per acre of composted chicken manure as compared to 2,920 pounds per acre. The species concentrates N in excess of its needs, and increasing N can favor this weed relative to crops. Common lambsquarters also has a strong growth response to increasing K, and it is strongly competitive when K levels are high. The species tolerates a wide range of soil pH but tends to grow poorly on very acidic soils.

Soil physical requirements: Common lambsquarters is regularly found on all soil textures from sand to clay and peat, but it grows most vigorously on fine textured soils. It emerges best in a moderately rough seedbed. It tolerates some soil compaction and waterlogging but with reduced emergence and growth. The species tolerates salinity.

Response to shade: Common lambsquarters is intolerant of heavy shade, especially shortly after emergence. Plants react to shade by growing taller and allocating a larger proportion of tissue to stem and leaves and a smaller proportion to the inflorescence. Nevertheless, plants will still flower in dense shade, and shading that begins after the plant flowers has no effect on seed production.

Sensitivity to disturbance: Young plants are unable to survive mowing or trampling, and older plants re-grow poorly. They dry out quickly when uprooted.

Time from emergence to reproduction: Plants flower more quickly with short day lengths than with long days. Flowering occurred five to six weeks after emergence in Canada and 81 days after emergence in Wisconsin. Some seeds become viable within two weeks of flowering, and most are viable within three weeks. Early maturation may be triggered by protracted drought. Mature seeds usually remain on the plant for weeks to months before being released.

See also  How to buy weed seeds to grow

Pollination: Common lambsquarters is self pollinated or wind pollinated.

Reproduction: The plants set seeds over a relatively short period as they mature. A small plant (about 1 foot) can produce several hundred seeds, and large plants can produce more than 100,000 seeds. Plants growing at low density with cabbage, onions or without a crop produced 30,000–370,000 seeds per plant, plants in soybeans produced 30,000–175,000 seeds per plant, plants in corn produced 8,000–117,000 seeds per plant, and plants in rapeseed produced 175–2,250 seeds per plant. Within each of these crops, most variation was due to differences in growing conditions between years. Plant size at maturity decreases as the date of emergence is delayed, and seed production is closely correlated with total plant weight.

Dispersal: Because seeds of common lambsquarters often reach high densities in soil, they are easily spread between sites by soil clinging to large animals, shoes, tires and machinery used for farm operations and road construction. Seeds have been spread in ship ballasts. The seeds survive well in the digestive tracts of cows, sheep and pigs, and manure is commonly contaminated with common lambsquarters seeds. Some seeds will pass through chickens, sparrows and ducks. Seeds also disperse in streams and irrigation water.

Common natural enemies: In wet weather, damping-off fungi can kill large numbers of lambsquarters seedlings, particularly if they are shaded by a crop or mulch. Leaf miner damage (curved tracks on the leaves) is commonly observed but is rarely severe enough to check the weed’s growth.

Palatability: Young lambsquarters are highly palatable and can be used as a salad green or pot herb. The foliage is high in vitamin C, carotenoids and essential minerals. Seeds and dried flower heads can be ground and added to soups and breads. The cleaned seeds can be cooked as a grain or ground for flour. Plants can, however, contain oxalic acid and nitrate and can be toxic to sheep and pigs if large amounts are consumed rapidly.

Weed Characteristics Summary Table

Common lambsquarters
Growth habit Seed weight (mg) Seed dormancy at shedding Factors breaking dormancy Optimum temperature for germination (F) Seed mortality in untilled soil (%/year) Seed mortality in tilled soil (%/year) Typical emergence season Optimum emergence depth (inches)
tall, erect 0.50–0.72 Yes cms, li, at, ni 64–77 8–51 31–52 early spring to summer 0.1–0.2
Photosynthesis type Frost tolerance Drought tolerance Mycorrhiza Response to nutrients Emergence to flowering (weeks) Flowering to viable seed (weeks) Pollination Typical & high seed production (seeds per plant)
C3 low moderate no high 5–12 2–3 both 30,000 & 300,000

Table Key

General: The designation “–” signifies that data is not available or the category is not applicable.

Growth habit: A two-word description; the first word indicates relative height (tall, medium, short, prostrate) and second word indicates degree of branching (erect, branching, vining).

Seed weight: Range of reported values in units of “mg per seed.”

Seed dormancy at shedding: “Yes” if most seeds are dormant when shed, “Variable” if dormancy is highly variable, “No” if most seeds are not dormant.

Factors breaking dormancy: The principle factors that are reported to break dormancy and facilitate germination. The order of listing does not imply order of importance. Abbreviations are:

scd = seed coat deterioration

cms = a period subjected to cold, moist soil conditions

wst = warm soil temperatures

at = alternating day-night temperatures

Optimum temperature range for germination: Temperature (Fahrenheit) range that provides for optimum germination of non-dormant seeds. Germination at lower percentages can occur outside of this range. The dash refers to temperature range, and the slash refers to alternating day/night temperature amplitudes.

Seed mortality in untilled soil: Range of mortality estimates (percentage of seed mortality in one year) for buried seeds in untilled soil. Values were chosen where possible for seeds placed at depths below the emergence depth for the species and left undisturbed until assessment. Mortality primarily represents seed deterioration in soil.

Seed mortality in tilled soil: Range of mortality estimates (percentage of seed mortality in one year) for seeds in tilled soil. Values were chosen for seeds placed within the tillage depth and subjected to at least annual tillage events. Seed losses are the result of dormancy-breaking cues induced by tillage, germination and deterioration of un-germinated seeds.

Typical emergence season: Time of year when most emergence occurs in the typical regions of occurrence for each weed. Some emergence may occur outside of this range.

Optimum emergence depth: Soil depths (in inches below the soil surface) from which most seedlings emerge. Lower rates of emergence usually will occur at depths just above or just below this range.

Photosynthesis type: Codes “C3” or “C4” refer to the metabolic pathway for fixing carbon dioxide during photosynthesis. Generally, C3 plants function better in cooler seasons or environments and C4 plants function better in warmer seasons or environments.

Frost tolerance: Relative tolerance of plants to freezing temperatures (high, moderate, low).

Drought tolerance: Relative tolerance of plants to drought (high, moderate, low).

Mycorrhiza: Presence of mycorrhizal fungi. “Yes” if present; “no” if documented not to be present, “unclear” if there are reports of both presence and absence; “variable” if the weed can function either with or without, depending on the soil environment.

Response to nutrients: Relative plant growth response to the nutrient content of soil, primarily N, P, K (high, moderate, low).

Emergence to flowering: Length of time (weeks) after emergence for plants to begin flowering given typical emergence in the region of occurrence. For species emerging in fall, “emergence to flowering” means time from resumption of growth in spring to first flowering.

Flowering to viable seed: Length of time (weeks) after flowering for seeds to become viable.

Pollination: “Self” refers to species that exclusively self-pollinate, “cross” refers to species that exclusively cross-pollinate, “self, can cross” refer to species that primarily self-pollinate, but also cross-pollinate at a low rate, and “both” refers to species that both self-pollinate and cross-pollinate at relatively similar rates.

Typical and high seed production potential: The first value is seed production (seeds per plant) under typical conditions with crop and weed competition. The second value, high seed production, refers to conditions of low density without crop competition. Numbers are rounded off to a magnitude that is representative of often highly variable reported values.

Further Reading

Bassett, I.J. and C.W. Crompton. 1978. The biology of Canadian weeds. 32. Chenopodium album L. Canadian Journal of Plant Science 58: 1061–1072.

Henson, I.E. 1970. Effects of light, potassium nitrate and temperature on the germination of Chenopodium album L. Weed Research 10: 27–39.

Mohler, C.L., B.A. Caldwell, C.A. Marschner, S. Cordeau, Q. Maqsood, M.R. Ryan, A. DiTommaso. 2018. Weed seed bank and weed biomass dynamics in a long-term organic vegetable cropping systems experiment. Weed Science 66: 611–626.

Williams, J.T. 1963. Ecological Flora of the British Isles. Chenopodium album L. Journal of Ecology 51: 711–725.

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Weed seed germination lambsquarter

Lambsquarters (Chenopodium spp.) taxa

-Lambsquarters Outline
-Lambsquarters Bibliography (1991)
-Lambsquarters Bibliography (1996)
a. common lambsquarters (Chenopodium album)
b. mapleleaf goosefoot (C. hybridum; C. gigantospermum)
c. mexican tea (C. ambrosoides)
d. taxa: complex of associated species or demography?; Atriplex spp.?

4.16.96
Agronomy 517: Weed Biology and Ecology
Spring Semester, 1996
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Outline of the Biology and Ecology of

Common Lambsquarters ( Chenopodium album L.)

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Prepared by: Juan Medina P .
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Taxonomic hierarchy:

Kindom Division Subdivision Class Order Family Genus
Plantae-Tracheophyta-Spermatophyta-Angiospermae-Caryophyllales-Chenopodiace a-Chenopodium

Family Characteristics:
Chenopodiaceae species: annual or perennial herbs, often fleshy or woody. Leaves: opposite or alternate, entire, toothed or lobed. Flowers: perfect or imperfect and the plant monoecious. Inflorescence: spicate or axillary cymules. Sepals: 3-5 united, persistent, often enlarging in the fruit. Petals: absent. Stames: 5. Fruit: utricle.

Important genera: Chenopodium, Atriplex, Salsola. Provide important species of weeds in USA. Characteristics in filotaxia,leaf shape and fruit make the distintion among genera. About more than 20 species of Chenopodium are distributed in USA and around the world. Several of them considered toxic, for example C. Album cause: a) polen— summer hay fever; b) contain potentially dangerous concentration of N0-3 which probably in Iowa cause a seasonal disease of swine, perirenal edema to the ingestion of this weed. Another common weed C. Ambrosoides or “wormseed” from tropical America and now with a very wide distribution in North America, it is famous for its antihelminticum properties. The oil responsable for the antihelmintic action (compared by terpene Ascaridol), could be fatal in overdose in animals and people.

Chenopodium genus: Erect, annual or occasionally perennial, monoecious herbs. Leaf alternate, pinnately veined, often 3-nerved,petiolate. Inflorescence of paniculate spikes of cymules, the spikes 0.5-3.0 cm (rarely 10 cm) long. Sepals 5, persistent and tightly enclosing on the fruit. Stamens 5. Stigmas 2-3. Fruit utricule smooth to rugose. Seed horizontal (Radford,et.al.1968).

Chenopodium album
The most important weed of the entire family and in which this revision will be concentrated.

Geographical origin: Completely obscured as is its relation to other members of its genera for one or another reasons, it does not have readily identifiable centres of diversification. Moquind-Tandon (1840-1849), considered as a weed of agriculture throughout temperate regions.

Geographic distribution: cosmopolitan, ranked amongst the 10 most important weeds on the world Holm, 1977). Occurs in latitudes of 70*N and 50*S.

General description of the species: annual; 10-250 cm. High; stem: angular, branched, brownish-yellow and ridged with green or reddish parallel stripes; leaves: alternate, petioled, without stipules, nearly farinosa to nearly glabrous, deep green to light green, ovate lanceolate to rhombic -lanceolate,sinu-dentate to entire, lamina 1-12 cm.long, 0.5-8.0 wide, 1-5 times longer than wide. Plant : monoecious; flower: perfect, clustered in contiguos glomerules, 5 merous, farinose to glabrous, perianth basally united, clasping and nearly enclosing the mature fruit (utricule); Stames : 5, rarely 3 or 4; pistil having a short style and 2 papillate stigmas; seeds: mostly shiny black, horizontal, 1.2 mm wide by 1.3 mm long, circular in outline; testa with radiating faint rugalate ridges or smooth; pericarp easy or difficult to remove, mottled-farinose or smooth; brown seed, very small proportion; the same size, thin testa regulate ridges or smooth, less heavy.
Account of variation:
Unisexual female and male organs (monoecious) on the same plant.
Wind pollinated —> self and cross pollination.
Genoma —> Two ploidy levels –> HEXAPLOID 2n=54 most common
TETRAPLOID 2n=36 plus variable number of supernumerary B chromosomes
Atrazine – tolerant biotypes ( Canada and USA ) = n=27 with completly meiosis.
Aellen,1929; recognized 34 subspecies, varieties and forms in North America, and Abrams in 1944, concluded that all these taxa were minor variants of C. album . In Canada and North America C. Berlandieri 2n=36 and C. Strictum var. Glaucophylus are very related species with C. album
Hybryds: there is not evidence in the current revision that natural interspecific hybrids can occur. Artificially, Darmency and Gasquez obtained Hybrids between the two karyotypes of C. Album. They are mostly sterile and produce seeds of poor viability.

See also  Og dragonfly seeds

Habitat: —> Climatic growth conditions a) range of annual average precipitation—->30 – 325 cm. b) growing season –>30-200 days. c) range of degree days above 42 *F->1500-3500. Soil conditions –> strongly acid to alkaline, well-drained soils, preferently calcareous soils. Chernozemic, podzol or gleysolic soil type.
Occurrence —>It is found in growing in association with other weeds in disturbed open habitats. It is rare to find it in natural situations such as native woodland and prairie.

Wind-pollinated flowers, probably no insects; self compatible and reproduces both by self and cross-pollination.
Seeds: Seed production capacity >72400/plant and ~ 1428/g
Seed viability in the upper layer (9 in.)of cultivated soil in England = 73 – 12.9 Mill/ac. ( Roberst,1968). The extreme phenotipic plasticity make a plant reacts to the environment stress by varying the number of its parts, then an individual plant of C. Album may, under stress of nutrient deficiency; high density or drought conditions, flower and set seed when only it has 5 cm. high, but given more ideal growing conditions, may reach 1.0-1.5 m. hight and produce 50000 times as many seeds as its depauperate stressed counterpart.

Seed dispersion: no obvious mechanism for the dispersion of seed, it has been recorded arising from faeces of animals (cattle, pigs, sheeps, and in birds, seeds pass through their digestive system, increasing germination among 32 to 100%). The size and weight of the seeds allow them to be dispersed efficiently in land-crops by irrigation. Man is the main source of dispersion.
Seed dormancy and seed germination processes: diversefied and complex adaptive mechanims that allow Ch.album to survive and be succesful. It may remain viable in the soil for 1600 years ( Odum,1965 ). It can germinated over a wider range of conditions than the less weedy species of the genus.

Genetic control of innate dormancy: control through “Somatic Polymorphism” , common in many Chenopodiaceae species. In Chenopodium album: four types of seed in two colour categories: black and brown and two seed categories: reticulate and smooth. Brown seeds are: thin-walled, larger, germinate quickly even at low temperature. These
are among the first seeds to be ripened by the parent.
Black seeds are: * produced first for the plant under long day lenght; thick-walled, smaller and require cold or supply NO3 to break dormancy (William and Harper,1965).
Seedlings from brown seeds are commonly killed by winter cold or tillage, but, if they survive,produce very large plants with a higher reproductive output than black seeds. The proportion of black (97%) and brown (3%) seed suggest polymorphism is selectively favoured and probably environmental governed as in other genera (Williams and Harper 1965).

Viability of seeds: seeds produced under short days (8h), had 94% and 83% germination in the light and in the dark. Seeds produced under long day (17h), had 20 and 2% germination in the light and in the dark respectively. The inhibitin sustances were different in both photoperiods (8 and 17h.). Germination of 39 years old seeds was obtained by Toole and Brownin 1946, at 45-55 cm., and 90-105 cm. of the soil profile, where conditions of moisture , temperature, and oxygen were assumed to be nearly constant. Lewis,1973 found seed survival buried in soil for 20 years.

Soil Seeds emergence: % accumulated in a 5 years period = 18.5 almost 25 of the total emergenced at the first year (Chepil,1946)
Seeds germination: 1- growth regulators – cytochynins and gibberellins in the seed norm this proccess. This aspect was showed by Chu, et. al.,1978.
2- Light requirements : The influence of light on germination is conditioned by many factors and can not be considered as an isolate innate property of the black seeds. The nitrate supply, temperature, age and genotype of the seed are the complex that norms the effect of light on the germination. There are some aspects about, that must be important to be considered:
a) Seed color and dormancy: black seeds – have innate dormancy and need special treatment to germinate. They during the first year harvested have a strong dormancy influenced by such factors as light, moisture, and nitrates and gradually it become reduced as the seed age increase. Nitrate largely determines the response of young seeds to the light, and has more influence than alternating temperature. Constant t* (23*C), ligth and nitrates together promote germination of the young seeds (8-11 months old), which were insensitive to either factors applied separately. Old seeds (32-35 months), show good response to light and nitrate together and separately. After the response to nitrates, lambsquarter has similar features of innately ligth condition like other species: a) short light exposure requirement; b) positive light response with initial water uptake; c) insensitivity of dry seeds; d) decreased light response with prolonged imbibition in the dark. e) light temperature dependence; f) high temperature induction thermodormancy. Brown seeds – present no restriction to germinate in a suitable condition of water, oxygen and temperature (Henson,1970).

b) Spectral composition: the phytochrome system which controls the light sensitivity of germination in many species involves an interconversion of two forms of phytochrome, red light (ca 660nm), and far-red light (ca 730 nm) and probable important in the germination of seeds of Ch. Album could be that far-red light predominates over red under leaf canopies of crops.

d) Interactions: growth regulators and light- in C. album, seeds gradually lose their sensitivity to light and plant growth regulators (hormones) during induction into secundary dormancy. For example, incubating light requiring seeds in darkness led to a gradual decrease in GA4+7 and ethylene. Indicating that there is a gradual transition between non dormancy and dormancy in whatever internal processes light and plant hormones regulate. The germination inhibitors are located in the perianth of fruits that vave been initiated under long photoperiod (20h).
3- Nutrients in the soil.

Nitrogen and related compounds – Fawcet &;Slife, 1978.,found close correlation between rates of N applied and concentration of nitrate in lambsquarters seeds.they found also more seed germination 34% , in plots with previous application of N03NH4 compared
with 3% from unfertilized plots. It may be that stimulation of germination in seeds of C. Album , and a number of other species by nitrate is involved in the timing of field germination, because the NO3 concentration of the soil solution often rises quite sharply as the soil temperature increase in spring.

Oxygen –Lowered oxygen tension has also been held responsible for dormancy of buried seed. Severe starvation may mantain a dormant condition.
Revewing earlier works showed conflicting evidence that just can be explained by the complexity of this process and by the diversity of experimental conditions in which they occurred.
The factors covered in this revision are the most important issues that govern this phenomenon.

Crop-competition effect: the most important weed in potatoes and sugar beet on the world; in United States is very important weed in soybean, asparagus, corn, in Canada, it is important in several crops like: soybean, cereals (wheat, oat, barley etc.); european countries, England, French, germany, etc., mainly in cereal crops ; in Mexico, commonly found in cereal crops, corn, beans and in the establishment of alfalfa.

1- Recruitment of seedling population: High density of seedlings are normally found in crop fields early in the spring ( 0.8 – 0.2 mill/ha.), and they can continued germinating until late of the summer. As soon the crop or weed canopy start to cover or shaded the soil, the germination is inhibited. Microtopography had a marked effect on the relative establishment of the species, the behavior on the soil surface could be seen in the way in which it comes to the rest of species after sowing. The experiments established at this respect, emphasize a somewhat unusual aspect of seed size and shape as well as a neglected element of environmental variation in determining the size and quality of plant population.

3- Density-Mortality relationship: When plant population are grown at high density, some individuals often die. There are two categories according with the type of relation established among individuals in a population: a) density dependent or self-thinning : the mortality of some individuals in a population is due to the pressure of individuals of the same species, and b) density independent or alien -thinning: where the mortality of individuals from a specific species can be ascribed to the streess from the density of an associated species. C. Album shows a self-thinning relationship, where the survivors plant presented a negative relationship between the weight of survivors and density.

2- Weed -to- weed competition:
Redroot pigweed ( Amaranthus retroflexus L.) and Common Lambsquarters ( Chenopodium album L.) are common associates in the weed community that grow in many parts of the agriculture’s world. Their behavior in the field,growing together, can be expected to vary from year to year,mainly according with the temperature in the early period of their association, and this temperature is related by the time of planting. Interesting work was done by Chu, et. al.1978b, finding:
Pigweed germinates: much more rapidly than lambsquarters under higher temperature.
much more slowly than lambsquarters under the lowertemperature.
Lambsquarters grow: the same like pigweed under lower temperature
slower than pigweed under higher levels.
If either weed has a time advantage over the other, it completely suppresses the later planted species.
In midwest dry spring,early planting, cool temperature —Lambsquarters problem
wet weather, late planting, warmer temperature —Pigweed problem
This confirmed that C3 plant C. album was better adapted to shade and cool temperature in fertilized fields than A. retroflexus, a C4 species. Corn a C4 plant suffers severe competition by early germinating C. album under the climatic conditions of central Europe. The C4 weeds A. Retroflexus and E. Crusgalli , only have chance if Chenopodium is removed. In this case , time of germination is most crucial for success in comprtition and not the C3 or C4 pathway.
The differences in germination and growth of the two species in response to temperature, explain their competitive ability,remember us that data on growing conditions are needed for valid comparison of weed population among experiments (Aldrich, 1984). The makeup of the weed community to change somewhat from year to year is a common situation even under monoculture and even though the seed bank become constant from year to year, this just could be explained by the way in which each member of the community sense the environment in a specific term of time and space. The relationship between lambsquarters and redroot pigweed is a very didactic example of the what was said before.

See also  Starting weed from seed

Response to weed control practices

Extensive inputs of tillage and herbicides are used to control C. album, mainly in summer annual crop production system around the world. The crop production system environment could be much of times characterized by high fertility , annual disturbance , production in rows , and herbicide use . In these scenary of conditions, the dynamic of population of C. album, respons in a successful or failed form, according with its biological characteristics interacting with the efficacy of weed management practices.

Polymorphism as a response to the tillage practices
The general responses of common lambsquarters to the tillage presure is inconsistent and some times contradictory. The classic studies of Roberts and his team, showed that, if all seeding of weeds is prevented, then progressive reduction in the number of viable seeds in the soil accurred due at tillage effect. The rate at which it occurs will depend of the species, frequency, and time of cultivation. In C. Album, it was 40% and it was less affected for more than one culivation. They also found that the viability of the Lambsquarters seeds decresed more in a Not-Tillage condition. Results showed by Buhler (1995),indicated that in soybean grown in rotation with corn, common lambsquarters densities were affected by tillage at one location, but not at another location with similar edaphic and cropping history, where no tillage land showed less density. Probably the explanation given by Fawcet (1987) could help in understanding this facts. He said that species that germinate under cool soil conditions, may be prevalent in no tillage fields prior to crop planting. This may allow them to suppress later emerging weeds or a significant portion of the population may be destroyed by tillage or herbicides prior to crop planting. Therefore, the effects of planting date and spring soil temperature in C. Album , germination prior to crop planting , probably caused the inconsistent responses observed among studies (Buhler,1995).

Polymorphism and herbicide resistant
Resulted of the intensive use of herbicide in the C. Album population, soon brought the appearance of biotypes resistant to the triazine group of herbicides.
The repeated use of triazine herbicides assumably has favored the selection of existing resistant plants or mutants. Darmency and Gasquez (1990)show out a revision of appearance and spread of triazine in C. album , indicating that, the more polymorohic the population is, the more likely that it can adapt to new agricultural stress.
One aspect of the polymorphism of this species,is the simultaneous presence of two ploidy levels in each population.the most common karyotype is hexaploid, 2n=54 , corresponding to the species voucher type; the other is tetraploid, 2n=36 plus a variable number of supernumerary B chromosomes . The tetraploid type does not correspond to any described species in Europe. As it can not be distinguished from typical C. album by its morphology but flower sooner, it can not correspond to the tetraploid lateflowering goosefoot C. Strictum Roth. var. glaucophyllum (Allen) H.A. Wahl. For which Atrazine-resistant population were found in Canada.
However, the two ploidy levels belong to the same biologycal species, they do not interchange genes in the field because the carrying pollen by the wind is very resticted in this plants. Thus, low heterozygosity may be expected so that a field population can be considered as just a mixture of different genoypes evolving separately. Due to the low outcrossing rate in corn fields, no gene exchange has occurred between resistant plants and adjacent susceptible population.
Another side of the polymorphism of C. Album populations is revealed by isozymes analysis. Using no more than four enzymes, nearly 60 different types of hexaploid plants in a survey of just two population in France, with an average of 23 genotypes per population.
The appearence of resistant plants within population of C. album , is not at random but depends on the presence of some unusual genotypes that can give rise to psbA gene- mutants with a higher frequency than expected with random mutation alone. It shows one of the most widespread resistant infestation.

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