Ways of distribution of weeds. Biological features and distribution of weeds Ecological biological features of weed seeds

From one place to another, weeds penetrate with the help of seed (seeds, fruits and seedlings) and vegetative primordia (roots, rhizomes, tubers and bulbs).

Vegetative primordia are most often formed in the soil and therefore cannot cause a rapid spread of weeds over long distances. Roots and rhizomes, growing in all directions, cause a gradual spread of root shoots and rhizome weeds. In this way, weeds can enter the fields only from adjacent borders and roads. The capture of the area in this case is extremely slow. For example, curtains of such root plants, like pink thistle and blue molokan, with the growth of roots in a year, they increase in diameter only by 2-3 m.

Weeds spread even more slowly with the help of tubers and bulbs. These organs of vegetative reproduction grow mainly on short underground shoots. One such rudiment forms a very small curtain, which then grows rather slowly.

Weeds spread most quickly and over long distances with the help of seed germs. The latter can spread from where their mother plant grows, depending on the biology of the weed, for several kilometers or much further. Thus, the seed method of distribution is the main one. weeds.

The main ways of seed dispersal of weeds are: scattering when shedding, the transfer of separated seeds by wind, water, animals, birds, and as a result of improper human activity. Seeds scatter when swaying mother plants(oats, cockle and the like), sharp twisting of the valves of opening fruits (peas and others), a number of other devices (Fig. 9). When the plants are swaying, the seeds fall off in the immediate vicinity of the parent weed, usually no further than 80 cm. When the fruits crack with twisting of their valves, they are scattered over a distance of several meters (in one of the experiments of the Research Institute of Agriculture of the South-East - 3 m).

To spread by wind, some weeds have parachutes made of hairs or special lionfish, others rise into the air due to the small size and lightness of the seeds, and others form large spherical elastic bushes - tumbleweeds. Of the juveniles with hair-flying, the most widespread and dangerous are, first of all, lettuce, Canadian small-flowered and goat-bearded, and from root-weeds - sow thistle and blue molokan. Less harm is caused by dandelion, roofing skerda, tartar, crosswort and others (Fig. 10).

These weeds outgrow their herbage shortly before the maturation of agricultural crops and enter the upper layer. Therefore, from the baskets that rise above the crops, their achenes can be torn out by gusts of wind. Seeds in baskets hold quite tightly. They blow out only when the wind is strong enough to lift them into the air. First, one achene is pulled out of the basket, followed by others with greater ease. This is a kind of biological adaptation that does not allow insemination of weeds in calm weather, when the transfer of seeds through the air is impossible.

Especially easily rise into the air the seeds with flyers when hit by the reel of harvesters. Having risen into the air, the seeds hover for a long time and can be transported over long distances (up to 3 or more kilometers). In windy weather, they fly for a long time without landing on the ground. If the weather is changeable, the wind carries them as if by leaps. They sit down, then they are driven by the wind along the ground itself, then they rise again into the air.

Certain conditions are necessary for the final landing of achenes with volutes. They do not linger on the bare surface of the soil; they settle into the stubble in single quantities, while in crops - in somewhat larger ones. From being blown away by the wind to being embedded in the soil, here they are protected by the herbage of cultivated plants. Completely delayed (even in windy weather) achenes with voles on forest edges and in forest belts.

The foci of lettuce, thistle, molokan and other weeds with bats do not appear in all places where their achenes settle. For example, in the fields they appear very rarely and not large quantities, since the conditions for their formation are unfavorable here: with deep plowing, they often cannot form seedlings, while with shallow incorporation, they need high temperatures for germination, and by the time the soil warms up, they find themselves in a dry environment.

These weeds germinate most abundantly and form large foci on various kinds fringes. Here, due to the lack of tillage, their seeds are concentrated in surface layer, which for a long time is fed by melt water from snow held up by trees. As a result, by the time the earth warms up to optimal temperatures their achenes are in favorable conditions for germination and seedling formation.

Sometimes weeds brought to the edges by the wind from very distant places form primary centers here, which, if you do not take measures, grow from year to year and become very large. Inseminating neighboring fields with a huge number of their rudiments, weeds eventually cause their clogging.

Examples of weeds with lionfish, that is, with a wide membranous border around the seed, are hogweed and parsnip. The wind lifts the seeds of these weeds into the air quite easily, but still carries them to shorter distances than the seed germs with voles. Possessing less volatility, weeds with lionfish settle on the fields in relatively large quantities and therefore can form primary foci both along the edges and in crops.

The wind carries small and light seeds over fairly long distances, although they do not have special adaptations for this method of distribution. Of the weeds that settle in this way, broomrapes are of particular danger. They can spread in this way, but only with a strong wind, amaranth, quinoa and gauze. As you know, strong winds often blow in the Volga region in August and September, raising clouds of dust. With them, the seeds of the listed weeds are transferred.

Many crop weeds: kurai, katun, ustel-field (stag), white amaranth, eryngium, cutter and some others are carried by the wind in the form of tumbleweed. The sphericity of the bush in these weeds occurs because they grow strongly side branches and in some cases several neighboring plants are linked. In autumn, by the time the seeds ripen, the main shoot of the listed stubblers at the soil level becomes very brittle. Therefore, even a relatively small wind tears them from the root and rolls across the field for quite long distances. At the same time, seeds are lost, scattering over the site. Tumbleweed bushes linger in ditches, road ditches, near forest belts and hedges. Here the largest number of seeds of these weeds remains and their main foci are formed.

Many weeds are spread by rain, spring and irrigation waters, because their seeds, fruits, stems and even twigs can float. The buoyancy of the seed germs is provided by special devices. For example, wild oat and a number of other cereals, as well as sedge weeds, have air under the flower scales. As a result, they float until the air is displaced by water. Sorrel fruits are able to swim because they have cork outgrowths and lionfish. The buoyancy of the seeds of amaranth, dodder, and many other plants is due to their non-wetability.

The ability to swim in different species is far from the same. Seeds of field yarutka, amaranth, gray hiccup, snakehead, blue molokan and a number of other plants can stay on the surface of the water for about a week. Then, for about seven days, single seeds sink in them. In mass quantities, these weeds settle to the bottom of the reservoir much later.

Separate seed rudiments of chicken millet, gray mouse, splayed bonfire, garden sow thistle, stag, tenacious bedstraw and shiny quinoa begin to sink after five days. In significant quantities, they are immersed in water only after two to three weeks. In wild oats and green mice, some seeds sink already in the first days of being in water, while the bulk - after about 7-10 days. Thousand-headed and goatbeard sink even faster, on the fifth or seventh day. The seeds of field bindweed, cockle and small-fruited camelina have the least buoyancy. In the first two weeds, about 70-80% of the seeds sink in three days, and in the last one, everything.

The fruit and twigs of most weeds float much better than the seeds. So, creeping bitterweed baskets in mass numbers begin to sink after a week in water, and seeds - already on the second or third day. Field bindweed pods float as long as bitterweed baskets, but the seeds sink more than half already during the first two days.

Good buoyancy, first of all, ensures easy transfer of freshly shed seed buds by rainwater flows. First, seeds, fruits and seedlings are carried into watercourses, and then along them to neighboring areas. As a result, foci of weeds, the seed rudiments of which have good buoyancy, are formed primarily along watercourses. Under our conditions, weeds spread by streams of rainwater over distances, most often not exceeding 1-2 km. Only on farms with rugged terrain can heavy rainfall bring seeds much further.

Rainwater usually disperses freshly shed seeds, as they are highly buoyant. In the future, their ability to swim gradually deteriorates. Despite this, melt waters also play a certain role in the dispersal of weeds. They carry the rudiments of weeds mainly from uncultivated lands (on arable land, the seeds are planted in the soil). Spring waters, in particular, carry the baskets of creeping mustard and other composite plants. Hollow waters play a certain role in the distribution of weeds growing in floodplains.

Irrigation water contributes to the spread of weeds growing along the edges of irrigation canals. Their seed germs fall into canals, irrigation waters lift them up and bring them to the fields. It is estimated that several million weed seeds can pass through channels 3-4 m wide per day. The first portions of water are the most clogged, as they carry the bulk of the seeds accumulated at the bottom of the canals during the inter-irrigation period.

Many weeds are spread by animals. The fruits of Velcro, tenacious bedstraw, succession, tenacious mouse, cocklebur and others are different kind thorns and thorns. With them, they cling to the fur of animals, which carry them to new areas (Fig. 11). The seeds of some weeds (amaranth, quinoa, white gauze, mice, field mustard, sparrow, buckwheat, sorrel, chamomile and others) are poorly digested by animals, such as horses and large cattle. Therefore, these weeds can get on agricultural plots when animals graze on them and use the latter in field work.

Especially far seeds of weeds can be carried by birds. In the experiments of the Research Institute of Agriculture of the South-East, a large number of seeds of amaranth, mari white and chicken millet were found in the goiter of sparrows. A significant part of them turned out to be not only viable, but also possessed increased germination. Worst of all, sparrows digested amaranth and quinoa. That is why when sparrows visit fields, foci of amaranth and quinoa are formed. From these foci, weeds gradually spread in all directions.

In large quantities, weeds are brought to fields with manure and bird droppings, if they are used as fertilizer without special pre-training. Seed rudiments of weeds get into manure not only because, when weeding forage is etched, some part of them is not digested by animals. They end up in manure when bedding containing weeds is used, and also due to the fact that animals, choosing a more palatable feed, throw weeds out of the feeders.

The following figures show how real the possibility of spreading weeds with manure is. In the experiments of the Institute Agriculture Southeast in 1 kg cow dung 1875 seeds of various weeds were found, including amaranth - 1800, chicken millet and mouse - 50. Of these, 37-45% of the seeds turned out to be viable. This means that when 40 tons of such manure are applied per hectare of arable land, 28-34 million live seeds of amaranth, chicken millet, mice and other weeds will be introduced.

A large number of live seed germs of weeds also contains bird droppings. It is estimated that when 7 c chicken manure along with it, an average of 10-15 thousand seeds of various weeds are brought per hectare.

The spread of weeds can occur when misuse machines, containers and transport. Weed seeds are driven into the augers, under the slats of the canvas conveyors, into the openings of the sieves, the cells of the trieres, various grooves and slots. When such machines are used for harvesting clean crops or cleaning grain, weed seeds from their places of accumulation in some part are thrown into the field or fall into the grain. As a result, pockets of weeds appear on clean lands.

Weed seeds remain in bags and bins. So, in each empty bag, previously filled with wild oat, from 150 to 200 grains of this weed were found, huddled in corners and clinging to the fabric. If in a container and a granary without them pre-cleaning pour clean seed material, then it becomes clogged to a certain extent. As a result, when it is sown, weeds can be brought to the fields.

Weeds spread during the transportation of weedy sheaves, grain, straw, hay, grain waste, chaff, bran. Getting lost along the roads, they sprout and grow along the edges of crops, from where they penetrate into the fields. In the largest quantities, highly loose small-seeded weeds, such as amaranth, white gauze and quinoa, are lost. This is one of the main reasons for their abundance along the edges of various roads.

For particularly long distances, weeds spread along roads during the transport of agricultural materials from one locality to another (often very remote). This, in particular, is the reason for the appearance of primary foci of bitterness near the roads along which hay was transported, and the presence of stingray in the right-bank regions of the Saratov region along railway lines, although this weed is not present in neighboring fields.

Weeds spread especially quickly over long distances and over vast areas when sowing seeds clogged with them. Seed contamination is the result of insufficiently thorough cleaning and inability to properly adjust grain cleaning machines. It is most difficult to isolate hard-to-separate weeds from seed grain.

There are other ways to spread weeds. Shiritsy, white gooseberry and quinoa grow in large quantities along the roads. Their seeds stick to people's shoes, to the hooves of horses and other animals, to the wheels of carts and cars. As a result, these weeds spread with incredible speed in different directions. This mode of distribution is one of the main reasons for their growth along the roads. The amaranth amaranth grows, for example, along roads precisely because it sticks to car tires.

All of the above shows that weeds penetrate arable land and other agricultural land in various ways. They are brought to the fields first of all when sowing poorly cleaned seed material. Therefore, the seeds must be cleaned in the most thorough way.

Many ways of spreading weeds contribute to the formation of foci of weeds in close proximity to agricultural lands. Such foci most often occur along the edges of fields, on the sides of various kinds of roads, along the edges of forests and forest belts, on vacant lands, estates of collective farms and state farms, land plots common use cities, towns, villages and villages, household plots collective farmers, workers of state farms and other enterprises; on banquets of irrigation and other canals, in reserves and on the right of way of highways and railways, and in many other unsown places.

In order to prevent the penetration of weeds into fields and other agricultural lands, it is necessary to apply general cultural preventive measures. The task of the latter, in addition, is to prevent the introduction of weeds with manure, bird droppings, as well as during grazing and harvesting.

The widest distribution of weeds is primarily due to their enormous fertility. While, for example, one cereal plant, even with the best cultivation, is capable of producing on average only about 2000 grains, the fertility of most weeds is immeasurably higher, as can be seen from the following data showing how many seeds or fruits it produces one weed.

Further, weeds are endowed with special and varied adaptations for dispersing their seeds over as wide a space as possible.
One plant produces fruits or seeds
Rye brome (Oromus secalinus)....... 1 420
Doll (Agroslemma githago)......... 2 500
Gray mice (Selaria glauca) ........ 5 520
Cornflower (Centaurea Cyanus/....... 6680
Buckwheat (Polygonum convolvj/us L.) 11 200
White Dawn (Lychnis alba) ......... 14690
Field sow thistle (Sonchus arvensis)....... 19000
Krgstovnik is ordinary. (Senecio vulgar is) ... 20,000
Common flaxseed. (Linaria vulgaris)..... 32 300
Budyak (Cirsium aruense)........... 35 550
Mullein (Verbascum lychnitis)......... 40 000
Odorless chamomile (Matricaria in odor a) .... 54000
Shepherd's purse (Capsella bursa pastoris/ .... 73 OEE
White quinoa (Chenopodium album) ...... 100000
Wormwood (Artemisia Absinthium) .... 102000
Chernobyl (A. vulgaris).......... 143000
Shnritsa (Amarantus retroflexus) ........ 500 000
Walker (Sisymbrium Sophia)........ 730 OEE
In some weeds, this dispersal is achieved by a special arrangement of their fruits, which scatter seeds, as, for example, in peas, etc.; in wild oats, due to twisting and unwinding of awns, from changes in air humidity, grains can not only crawl, but even burrow into the ground. It is known how strongly the grains of wild oat are stuffed into the corners of the sacks or into parts of the machines, and from here they can also fall into other grain, poured into the same sacks or cleaned on the same machines.
At the same time, weed seeds can be carried by water, wind, animals, etc.

With the help of water, weed seeds can not only spread over the surface of the earth, as, for example, during rains in hilly areas, but also penetrate deep into the soil, when, for example, after a severe drought that forms many cracks in the ground, heavy showers. In irrigated areas, weed seeds and even whole parts of plants are dispersed by irrigation water.

First of all, the wind can roll over the surface of the earth not only individual fruits and seeds, but even entire bushes of weeds, forming the so-called. "tumbleweed", as it is observed in our steppe regions, where, picked up by the wind, numerous bushes of kurai, kachima and many others rush through the fields in autumn. All this usually accumulates near any obstacles encountered on the way, near ditches, hedges, in ravines, etc. That is why the borders and various other abandoned places differ among us in many weeds.

Even more often, the fruits or seeds of weeds are picked up by the wind and carried through the air, due to the lightness of the seeds, or due to the various hairs and tufts that are provided, for example, with achenes:
sow thistles, budyakov. dandelion and more etc. All these flying seeds at the same time stick to the dress, ...

High fertility.Most of the weeds have an increased ability to reproduce. According to acad. A.I. Maltsev, some weeds are able to give great amount seeds. If in crops one plant of winter rye is able to form 120â?”200 grains, fiber flax â?” 60â?”100 seeds, then one rye brome plant can produce 1420 seeds, blue cornflower â?” 6820, thistle field â?” 19 thousand, odorless chamomile â?” 54 thousand, mari white up to 100 thousand seeds, curing up to 200, and one well-developed plant of upturned amaranth can produce up to 500, striated goluvka up to 730 thousand. According to seed productivity, all young weeds are divided into 3 groups. The first group includes weeds that form on average from 50 to 600, up to a maximum of 15 thousand seeds. These are common cockle, gray foxtail, wild radish, bindweed mountaineer, etc. In height, they are plants of the middle tier. The second group consists of weeds that give an average of 600 to 1500 seeds with a maximum productivity of up to 100 thousand seeds. These include field yarutka, field mustard, shepherd's purse, gray hiccup, etc. The third group includes weeds, the average fertility of which is from 1.5 to 5 thousand seeds, and the maximum is up to 1 million seeds. This includes black henbane, white gauze, upturned amaranth, Canadian small-flowered, etc.

However, their fertility depends on the growing conditions. Weeds reach their highest fertility at fertile lands in crops of tilled crops, near roads, irrigation canals, on uncultivated lands with good supply of moisture, light, temperature and food regimes. Late weeds develop well in crops of tilled crops.

Unfriendly seed germination and uneven ripening. Weed shoots appear from early spring to late autumn. This is facilitated by various temperature and light conditions, varying degrees soil moisture, seed diversity (the phenomenon of heterocaria). Weeds such as common wild oats, white gauze, bindweed herb, etc. in early spring sprout in early May, and in a cold long spring - in the second half of May. Seedlings of more heat-loving weeds (chicken millet, upturned amaranth, gray foxtail) appear in late May - early June, and the seeds of winter weeds germinate only in the second half of summer. The extended period of seed germination is explained not only by their different attitude to external conditions, but also by the polymorphism of the seeds. For example, on one plant of white mari there are three types of seeds: large, medium and small. Some of them (large ones) germinate in the year of maturation, others (medium ones) - in the second year, and small ones in the third year and later.

Acad. A.I. Based on a review of works by a number of authors, Maltsev concludes that for the seeds of most weed species, the optimal depth for seed germination is 0-5 cm, for some species - up to 10 cm. Above 10 cm, most species do not germinate, as they usually have small seeds.

V.P. Tomilov found that the greatest number of seedlings of wild oat was obtained at a seeding depth of 5-10 cm. Seedlings from seeds embedded deeper than 20 cm did not break through to the surface.

Field germination of small-seeded weeds depends very much on the depth of incorporation. According to N.Z. Milashchenko and I.N. Cousin from a depth of 3-5 cm gave rise to 67.2-66.5% of the foxtail seeds, from a depth of more than 5 cm, the seedlings did not reach the surface and all died. Shoots of weeds from a depth of 10-15 cm appear with a great delay and look more weakened, oppressed.

Ways to spread weeds Weeds are spread most often by seeds and less often by vegetative organs. Ripened seeds are scattered during the rocking of plants by the wind, when mowing, sharp cracking of fruits, moving the mowed mass of weeds. Spherical bushes of some weeds (saltwort, stag, white amaranth, eryngium) cut off from the ground after the seeds ripen roll across the field with the wind, the seeds stick with mud to shoes, animal hooves, wheels Vehicle. The resettlement of weeds can also occur with poor cleaning of the working bodies of machines, with poorly cleaned seed material, unripe manure and bird droppings. The presence of various adaptations in seeds allows them to spread over considerable distances (Fig. 4). The spread of seeds and fruits of weeds is carried out either with the help of special devices in plants â?” autohorn, or with the help of various agents â?” aplohorno. In autochora plants, the dispersion of seed primordia occurs with the help of various devices actuated by mechanical forces. So, in field mustard, field cabbage, wild radish, levkoy icterus, odorless chamomile, seeds and fruits are scattered around mother plants under the influence of gravity â?” autobarochornally. Mechanical scattering of seeds, due to the tension that occurs in the drying integumentary tissues of fruits, is observed in the cicuta stork, field violet, narrow-leaved pea and other weeds. With the help of wind â?” anemochornoâ?” Seeds of medicinal dandelion, wild watercress, common ragwort, small-flowered canadian and many other weeds from the Compositae family are distributed. They are equipped with feathery bats, thanks to which they can be transferred to the surrounding fields and distant territories even with a weak wind (Fig. 4). The seeds of thistle, dandelion are equipped with bats, with the help of which they are carried by the wind. Seeds and berries of many weeds are spread with the help of animals, birds, insects, i.e. zoochory. Fruits or inflorescences of Velcro blackberry, with the help of which they cling to animal hair, human clothing, bird feathers and are transferred to neighboring fields and new habitats.

Vegetative propagation of perennial weeds. In the soil, along with seed primordia, there are roots of perennial weeds (rhizomes, bulbs, nodules, etc.), capable of vegetative propagation and called breeding roots. The high ecological plasticity of these weeds is determined both by the quantitative abundance and the high regenerative ability of the propagation roots. In many of them, a significant part of such roots is also located in the subsurface layer, often penetrating to a depth of 1–2 m or more. As a result, a large part of the root system is inaccessible to soil-cultivating tools, the working depth of which usually does not exceed the thickness of the arable layer. In the roots of reproduction, plastic substances are stored in the form of carbohydrates, the content of which, depending on the type of plant and the growing season, ranges from 5â?”12 to 35â?”54 %. They form a large number of adventitious (adnexal) kidneys. When the roots are damaged by tillage tools, some of these buds awaken and form new plants instead of the destroyed ones. During processing, the propagation roots located in the arable layer are torn and crushed into fragments of various lengths. Under favorable conditions, these segments are able to take root and even form independent plants. The reproduction roots of field sow thistle, couch grass, Tatar lettuce, field horsetail are characterized by high survival rate, while the survival rate of such roots in creeping mustard, field thistle, field bindweed is very weakly expressed.

With a decrease in the size of root segments, their ability to regenerate decreases. Nevertheless, the propagation roots of a number of perennial weeds (field thistle, couch grass, etc.) are capable of regeneration even with a fragment length of 1–5 cm.

Moreover, the strong crushing of the roots of perennial weeds stimulates awakening in their segments. a large number adventitious kidneys. As a result, the regenerative capacity (determined by the number of shoots formed per 1 m2) of propagation roots increases by 1.5–2 times or more.

Therefore, occasionally held in clean couple tillage or careless inter-row cultivation of tilled crops leads to a strong overgrowth of these fields with weeds.

With a decrease in the length of the roots of reproduction, and consequently, with a reduction in stocks plastic substances their survival rate decreases sharply. Therefore, the crushing of the roots and their subsequent incorporation into the soil to a depth of at least 20–25 cm almost completely exclude the regeneration of perennial weeds from the arable layer from segments of their propagation roots. This is the basis for the mechanical destruction of perennial weeds, called suffocation method. With minimal and zero technology, to destroy such weeds, one has to resort to chemical methods struggle.

The survival rate of fragments of propagation roots sharply decreases with an increase in soil density (above 1.1 g/cm 3), a decrease in soil moisture (below 15–20%) and temperature (below 5–10 °C).

High ecological plasticity is observed in perennial weeds and in unfavorable periods of their life. With deep mechanical damage to the roots, excessive soil compaction, prolonged drought root system creeping mustard, field thistle, field thistle, Tatar lettuce, field horsetail falls into a dormant state for 2–3 years. With the onset of favorable conditions, the remaining part of the root system resumes the regeneration of underground offspring, from which full-fledged plants are then formed. This explains the often unexpectedly abundant appearance of perennials on plowed fields, the presence of which in crops in previous years was practically not observed.

All this determines the high viability and stability of perennial weeds, if they are controlled without taking into account their biological and ecological characteristics.

Seed longevity. If in cultivated plants, in particular cereals, seeds during storage remain viable for up to 5 ... 10 years, then in most weeds, once in the soil, they are viable for several decades. Thanks to the hard shell, the seeds remain viable for a long time, regardless of soil moisture. Shell hardness is a biological property that is inherited. This property is most characteristic of some species of the legume and mallow families. With mechanical damage to the waterproof shell, seed germination is accelerated.

The longevity of seeds is also explained by the presence of dormancy. For example, wild oat seeds remain viable for 4-5 years, white mari - 20, field mustard - 7 years, wood lice - 10-15 years.

Distinguish between deep and forced rest. The first is related to the physiological state of the seed and the structure of the shell. The second is due to unfavorable external conditions(lack of moisture, air, heat, light). The destruction of seed coats contributes to their faster exit from dormancy.

Biological and forced dormancy of seeds. One of the characteristic features of most weeds is â?” unfriendly seed germination. If their seeds germinated as amicably as in cultivated plants, then it would be much easier to deal with them. The main reason for unfriendly germination is â?” the presence of a period of biological rest, when physiological and biochemical processes are weakened. Such a period in the life cycle of seeds is determined by a number of reasons: water and air impermeability of seed coats, high osmotic pressure of cell sap in seed coats; physiological immaturity of the embryo; availability in different parts seed inhibiting substances, the so-called inhibitors, which delay its germination; the isolation of protoplasm, the elements of which have not yet been included in the metabolism of the whole organism. From a general biological point of view, the dormant period of weed seeds is a way of adapting the body to maintain viability in adverse conditions, one of the ways of self-regulation of life processes in the body. A long period dormancy in weed seeds is of particular importance for the conservation of the species.

The rest period can be broken under the influence of light, variable temperatures, high frequency currents, mechanical or chemical destruction of the shell. In order to bring viable weed seeds out of the dormant period, it is necessary first of all to provide air, heat and water access to the embryo and reserve nutrients. Some factors (frost, periodic changes in temperature and changes in the humidity of the environment) open access to air, heat and water, since under their influence the permeability of the seed coat increases. Frost has an effect only on the wet shell, because it increases the activity of enzymatic processes in swollen seeds. The favorable effect of the alternation of frosts and thaws in winter periodâ?” one of the most important reasons for the high energy of germination in the spring of weed seeds wintering in the soil. Frost has little effect on dry seeds, so in spring they germinate slowly and in smaller numbers.

In addition, there is a forced rest. Compelled(secondary or ecological) peace in seeds and fruits is usually caused by the absence of a favorable combination of external environmental factors, which contributes to their germination (lack of moisture, excess heat, lack of light, the presence of plant inhibitors produced by other species, etc.). Unlike cultivated plants, the seeds of which must have a high germination rate, weed seeds have a very extended germination period. The prolongation of the germination period is also preserved in weed seeds that are constantly in the soil.

Many of the weed fruits that have fallen into the soil find themselves in unfavorable conditions and die. A significant part of the remaining fruits is able to remain viable in the soil for a long time and this causes clogging of crops of subsequent crops for several years to come.

Seeds of most cultivated plants usually remain viable for no more than 4–7 years and if stored indoors under optimal conditions. The seeds and fruits of many weeds do not lose their viability even after many years of being in the soil.

The unusual longevity of weed seeds is evidenced by the data of an experiment established by W. Bill as early as 1879. at Michigan College (USA). It has been established that the seeds of medium stellate, field mustard, shepherd's purse, upturned amaranth, yellow sweet clover remained viable after 30 years of burial in the soil, and the seeds of field bindweed, curly sorrel, black mustard did not lose their germination capacity even after 50 years under these conditions.

Diversity. In some weed species, seeds or fruits formed in one inflorescence differ in morphological and physiological characteristics. (diversity, or heterocarp). This increases the ability of the species to establish itself in the developed territory and to be introduced into new agrophytocenoses. So, in white mari, seeds of three types are formed: large, flat, greenish-brown light tones, which germinate in autumn in the year of formation; medium in size, round-convex, with a thin shell, greenish-black germinate in the second year; very small, round-oval, thick black germinate usually in the third year and later. In the wild oat panicle at the ends of the branches, spikelets are formed with grains of different types according to biological characteristics. In the upper part of the spikelet, small dark-colored grains are formed, easily crumbling, their dormant period is up to 16–22 months. They form seedlings from a depth of no more than 10–12 cm, and the plants are similar in rhythm of development to late spring ones. The grains from the lower part of the spikelet are the largest, light-colored, crumble later and therefore clog the seed of the crop. The rest period of these grains is about two to three months, at the end of which they sprout together under favorable conditions, giving seedlings from a depth of 18–25 cm, and develop as early ripening plants. In the middle part of the panicle, grains are formed that are intermediate in morphological and biological characteristics.

In weeds from the aster family (compositae) (spring ragwort, large goat-beard, etc.), seeds that form at the center of the inflorescence (baskets) have less short period rest than those located at the edge.

Different-time ripening of seeds and fruits. In the process of natural selection, young weeds have developed the ability to complete their life cycle somewhat earlier than cultivated plants. This leads to the fact that already in advance (before optimal time crop harvesting), a significant part of the weed seeds formed on plants crumble to the soil. In addition, it excludes the possibility of directly removing these seeds from the field, as is easily possible with weed seeds that fall, for example, into the bunker of a combine when threshing grain crops.

So, in the crops of winter crops, one and a half to two weeks before they are threshed, the plants of wild radish, shepherd's bag, field yarut completely die off, and a large proportion of their seeds fall into the soil. A few days later, seeds of odorless chamomile, blue cornflower, field larkspur, rye fire, field broom, etc., already ripened on separate branches, begin to crumble onto the soil. The period of grain maturation in wild oat is very extended, and by the phase of full ripeness of wheat, when they start threshing the crop, almost half of the formed seeds entered the soil.

In the steppe regions of Russia, some weeds, such as barnyard grass, cockerel millet, gray bristles, upturned amaranth, Russian saltwort, are strongly suppressed in grain crops and almost do not form seeds. However, after the threshing of grain crops and with favorable nutritional and water regimes in the unshaved stubble and a short daylight hours they rapidly go through the life cycle and after 2â?”3 weeks form an additional 40â?” 60 million seeds per 1 ha, replenishing the stocks of weed diaspores in the soil. These weeds are called stubble.

Numerous studies have established that in the arable layer of soil in some fields there are seeds of 10â?”25 various kinds weeds with their total number from 120 million to 3â?” 4 billion per 1 ha.

Considering the huge potential stock of seeds and fruits of weeds in the soil, it is necessary to conduct systematic weed control. This is one of the most urgent tasks in agriculture in the near future.

Other biological features. In some weeds, the seeds do not lose viability after passing through the intestines of animals and birds, for example, small seeds that are not mechanically damaged by ruminants or are completely eaten by various birds. The seeds of some weeds are not destroyed after processing cereal crops or grinding grain into flour, especially with coarse grinding.

There is a group of weeds that are characterized by diversity (heterocarpy), and this feature is hereditary. These include white gauze, wild oat, brilliant quinoa (has three types of seeds), ragweed wormwood (six), medicinal dandelion (two), millet, bird knotweed, ragwort, etc. These seeds differ in size and color, have a different period of biological dormancy, their germination is different, despite the fact that they were formed on the same plant or even inflorescence.

Some weeds are characterized by mimicry, i.e., the external resemblance of their or individual organs, in particular seeds, with cultivated plants. This biological feature makes it possible to easily spread with seed. To separate such weed impurities, cleaning is required on special grain cleaning machines.

The formation of a group of weeds began with the advent of agriculture. In addition to the will of man, but with his participation, there was a gradual selection of such plants that adapted to coexistence with cultivated plants. The adaptation of weeds to life in the crops of certain crops proceeds along the line of ecological assimilation and ecological differentiation of weeds and cultivated plants in relation to each other. Having adapted to the life of a cultivated plant, many weeds have developed properties similar to them - winter, fury, close stem height, shape, size of seeds and other features. Some weeds have lost the ability to self-seed: their seeds are threshed together with the seeds of cultivated plants (for example, a large rattle) and then, falling into the soil, germinate. The assimilation of weeds to cultivated plants is widespread and is clearly seen in the example of specialized weeds. The cycle of their development coincides with the development cycle of a cultivated plant, the height of the stem is approximately equal to the height of the stem of a cultivated plant, and therefore the seeds fall into the crop, threshed and clog the grain of cultivated plants. The shape, weight, size of the rudiments of weeds, seeds, fruits are so similar to the seeds or fruits of cultivated plants that it is almost impossible to separate them using conventional cleaning methods.

The ecological differentiation of weeds and cultivated plants is explained by their differences in the nature of the use of space, light, moisture, nutrients, etc. Such differences can lead to the fact that weeds and cultivated plants develop without interfering with each other, or competition for life factors plants is weakly expressed. On the other hand, such differences may even positive action for the development of cultivated plants. For example, weed legumes enrich the soil with nitrogen, which can then be used by cultivated plants, weeds with strong stems can serve as a support, support for climbing cultivated plants, etc.

The main biological features of weeds, which explain their high ecological stability in agrophytocenoses and increased harmfulness, as well as distinguishing them from cultivated plants in terms of properties, are as follows. Weeds are characterized by an extremely high ability to reproduce under favorable growing conditions and have high fertility. Individual species of weeds produce tens and hundreds of thousands of seeds per plant, which is many times greater than the number of seeds per cultivated plant. So, one plant of field thistle can produce 35 thousand seeds, odorless three-rib - 54, upturned amaranth - 500, Sophia's descuria - 730 thousand seeds. If we take into account that cereals on average produce 50-80 grains and only under the most favorable conditions can produce up to 2000 seeds per plant, then the superiority of weeds in terms of fertility over cultivated ones is obvious. Under real conditions, in agrophytocenoses, weeds produce incomparably fewer seeds than indicated above, but it is quite enough for their total number in the soil to reach colossal values. Undoubtedly, many weed seeds, falling on the soil surface, die under unfavorable conditions for germination, however, high seed productivity determines their greater survival. Especially since distinctive feature weed seeds is the ability to remain viable in the soil for a long time. The period of germination of seeds of cultivated plants is calculated in days, while the seeds of many weeds can lie in the soil for years and even decades without losing their viability. According to the observations of P. A. Kostychev, out of 400 seeds of the shepherd's purse, only 75 germinated in 1173 days. The rest did not germinate, but retained their viability. Until the age of 60, the seeds of amaranth and plantain do not lose their germination. White sweet clover seeds can remain viable for up to 70 years. The property of seeds not to sprout for a long time, to maintain viability is explained by their dormancy, the physiological state of the seed, the structure of the seed coat (deep dormancy) or unfavorable conditions for germination (forced dormancy).

Germination of weed seeds often occurs non-simultaneously and is extended in time, which distinguishes weeds from cultivated plants. In a number of weeds, the phenomenon of seed polymorphism is expressed, i.e., they form seeds of various sizes. So, in white mari, for example, seeds of three groups are formed: large, medium and small. The first germinate in the first year, the second - in the second and the third - in the third year.

Seeds of some weeds are characterized by long post-harvest ripening. For example, for chicken millet seeds, the ripening period after harvesting of cultivated plants is five to six months, for wild oat seeds - three to four.

The seeds or fruits of weeds have various forms and devices with which they can spread over long distances. The seeds of some weeds have pubescence, tufts, with the help of which they are carried over great distances (seeds of thistle, dandelion, sow thistle, etc.), others have trailers or thorns and are carried by animals and humans with their help.

It should also be noted that important feature some types of weeds, as the ability to reproduce not only by seeds, but also by vegetative organs: rhizomes (pig, creeping couch grass, humai, etc.), root offspring (sow thistle, thistle, mustard, field bindweed, etc.), tubers. Vegetative reproductive organs, cut into small pieces, not only do not lose viability, but, on the contrary, their ability to form shoots increases. The data of AI Maltsev (Table 26) testify to what values ​​the number of vegetative buds per square meter of the most common weeds can reach.

Table 26

The number of vegetative reproductive organs in the soil per 1 m2

Many weed seeds remain viable in water, silage, haylage, and manure after passing through the intestines of animals and birds. The amount of weed seeds in manure, especially in fresh and slightly overripe manure, can be very high. It was noted, for example, that the number of weed seeds that fell from 60 tons of fresh cow manure per 1 ha was 1 million.

(Methodological guide for students of the Faculty of Agronomy)

Target of this manual is to systematize the material about weeds and speed up the assimilation of the material by students in laboratory and practical classes. AT tasks The course includes studying the harm of weeds using various types of weeds as an example, learning the various biological characteristics of weeds and instilling skills in planning measures to combat various groups of weeds, as well as systematizing knowledge about weeds in general.

The concept of weeds and their harmfulness

Weedy called plants that litter agricultural land and damage crops. Plants belonging to cultural species, but not cultivated in this field, are weeds.

Weeds that clog individual agricultural lands are called satellites, and when certain types of crops are clogged, they are called specialized satellites. Adapting to the life of cultivated plants, weeds have acquired many of the characteristics and properties inherent in cultivated plants: winter, fall, stem height, size and shape of seeds, seed shedding, etc.

On the territory of our country there are about 1400 species of weeds, in the Cis-Urals there are more than 120 species. The most malicious: field horsetail, field thistle, field thistle, bindweed mountaineer, blue cornflower, common wild oat, creeping wheatgrass, white gauze, medium chickweed, zyabra pikulnik, field bindweed and others.

Weeds in the struggle for living conditions cause great damage to agriculture:

1. The crop yield is decreasing. Loss of agricultural crops in the world from weeds and other harmful organisms make up for cereals - 500-510 million tons; potatoes - 125-135 million tons; vegetables - 78-79 million tons. or 30 - 40% of the total harvest and is estimated at 75 billion dollars.

The decline in crop yields is due to the rapid growth and development of weeds. They consume large amounts of nutrients and moisture. If available per 1 sq.m. 14 stalks of thistle field in the arable layer of 0-20 cm can contain up to 104 of its root suckers, which absorb almost 238 kg of nitrogen, 35 kg of phosphorus and more than 160 kg of potassium per hectare of arable land (O.N. Mirskova). And winter rye consumes only 31 kg of nitrogen, 14 kg of phosphorus and 26 kg of potassium to create 10 centners of grain. In this regard, the effectiveness of fertilizers is sharply reduced, since in weedy fields most of the nutrients are absorbed by weeds.

3. Weeds contribute to the development of pests and diseases of agricultural plants. For example, on the leaves of the field bindweed, white marijuana, thistles, the winter cutworm lays eggs, the caterpillars of which severely damage crops. Wild radish, rape, shepherd's purse and some weeds from the cabbage family contribute to the reproduction of ground fleas and cabbage aphids, causing great harm to cabbage, rutabaga and other crops. Creeping couch grass promotes the spread of wireworm, rust of grain crops. Weeds from the cabbage family are distributors of cabbage keel, false powdery mildew etc.

4. Many weeds reduce the quality of crops and agricultural products. Seeds of weeds with strong clogging of crops increase the moisture content of the grain, which leads to self-heating and spoilage. The presence in flour of even a small amount of ground seeds of common cockle, intoxicating chaff, black henbane makes it unsuitable for humans and animals. Flour obtained from oatmeal oats has a tart taste and a dark color. The admixture of caustic buttercup, horsetail and some other weeds in the hay can cause poisoning of animals, and the presence of sweet clover, garlic, bitter wormwood gives the milk a bitter taste. Unground wild oat grains can cause disease in animals, and even death. Rigid awns, getting into a humid environment, begin to unwind and screw into the mucous membrane, causing inflammation and damage to the mucous membranes of the digestive organs in animals.

5. Weeds reduce agricultural productivity. machines, make it difficult to carry out a number of agricultural / x. works. In fields littered with field bindweed, couch grass, and thistle thistle, additional tillage has to be carried out, while the traction resistance of tillage tools increases to 30%. On heavily weedy fields, it becomes necessary to increase the number of treatments, and multiple treatments lead to drying out, destruction of the soil structure. Green succulent weeds clog augers and elevators of combine harvesters, wrap around sprockets, cause downtime, machine breakdowns, delay harvesting, and increase crop losses.

Biological features of weeds:

1. The spread of weeds is facilitated by their fertility. A single weed plant, under favorable conditions, is capable of producing from several hundred to tens of millions of seeds, while a cereal plant produces, on average, several tens of seeds. According to Professor A.A. Khrebtov, the most common weeds of the Cis-Urals have the following fertility: medium chickweed (louse) - 25 thousand, sow thistle - 20 thousand, thistle - 35 thousand, odorless chamomile - 500 thousand, white gauze - 100 thousand, amaranth - 500 thousand, wormwood - up to 1 million seeds. Such a high seed fertility of weeds leads to severe clogging of the crop and soil, allowing weeds to retain their appearance even with active control.

2. Seeds of many weeds can remain viable and viable in the soil for many years. The durability and hostility of seed germination is an important biological property of the species and depends on the physiological state of the seed and the structure of the shell. The dense shell of the seeds of many weeds prevents the penetration of air and water into them, as a result of which the reserve nutrients of the seed are in an insoluble form and cannot be consumed by the embryo. From a state of rest, external conditions can lead: periodic changes in humidity and temperature, frost. At the same time, the seed coats become permeable to water and air and begin to germinate. Experiments have shown that wild oat seeds that are frozen in a wet state germinate better in spring than those frozen dry.

The dormancy period for different types of weeds is not the same, so wild oats remain viable for up to 8 years, white gauze, amaranth, shepherd's purse - up to 5-6 years or more, and sweet clover seeds remain viable for 77 years.

The arable layer contains huge stocks of weeds. In the experiments of the Department of Agriculture of the Perm State Agricultural Academy in the educational farm "Lipovaya Gora" on slightly weedy fields in the soil, there were from 45 to 65 million seeds per 1 hectare of arable layer, and on weedy fields of the Ochersky district of the Perm region - up to 1.5 - 3.0 billion.

3. Weeds are able to reproduce not only by seeds, but also by vegetative organs - rhizomes, root shoots, bulbs, fragments of stems, leaves. In some of the most malicious weeds - field sow thistle, field bindweed, creeping wheatgrass, field watercress, the vegetative propagation method is predominant (A.I. Maltsev). With the favorable development of wheatgrass, the length of rhizomes per 1 sq.m. arable layer reaches 495 m, weight - 2890 g, and the number of vegetative buds - 26000. Yellow thistle has a length of roots per 1 sq.m. reaches 76 m, weight - 1000 g, and the number of buds - 1600. Each bud, under favorable conditions, can germinate and give new above-ground shoots.

4. Weeds have various adaptations for dispersing seeds and fruits. Thus, the seeds of field thistle, thistle, dandelion and others are equipped with volutes, with the help of which they are carried by the wind from one field to another. In a number of weeds - tenacious bedstraw, Velcro, burdock, cocklebur, the seeds are equipped with thorns, with the help of which they cling to human clothing, animal hair and are transported over long distances.

Weed seeds are also spread by water during irrigation and when rivers flood. The source of clogging fields is also fresh, improperly prepared manure. Seeds get into manure with bedding and feed. The seeds of many weeds, when eaten by animals, pass through the digestive organs and do not lose their germination.

5. An important biological feature of weeds is unpretentiousness, adaptability to growing conditions. Cultivated plants show increased requirements for temperature, humidity, tillage, depth of seed placement, and weeds germinate at deeper placement, less moisture, lower soil temperature.

Weed seeds germinate from different depths, but the largest number - from a depth of 0-5 cm. The larger the seeds and fruits, the deeper they germinate and vice versa, the smaller the seeds, the less depth they can germinate. Wild oat seeds can germinate from a depth of 15 - 20 cm, and wood lice seeds - from a depth of 0.5 - 2.0 cm.

The seeds of most weeds ripen earlier than the seeds of cultivated plants and, crumbling before harvesting, fall into the soil. A lot of seeds fall off during harvesting.

As a result of a long evolution, the seeds and fruits of weeds have acquired sizes, shape, appearance, ripening terms close to the seeds of cultivated plants. The seeds of colza and wild radish are very similar to cabbage seeds, Tatar buckwheat to cultivated buckwheat, oats to wild oats, chicken millet to cultural millet, etc. This greatly complicates the cleaning and underworking of the seed and serves as a source of secondary clogging.

AGROBIOLOGICAL CLASSIFICATION AND CHARACTERISTICS OF WEEDS

For a more convenient study of weeds and the development of effective measures to combat them, a classification based on important morphological and biological characteristics has been created. It includes: method of nutrition, life expectancy, method of reproduction (Table 1).

Table 1

Biological groups of weeds (according to A.I. Maltsev)

DESCRIPTION OF BIOLOGICAL GROUPS OF WEEDS

underage weeds – reproduce by seeds, bear fruit once in a lifetime,