Dangers of damage to agricultural plants by diseases and pests. Damage to agricultural plants by diseases and pests
MINISTRY OF EDUCATION OF THE REPUBLIC OF BELARUS
EE "Mogilev State University"
them. A.A. Kuleshova"
Department of Physics and Technical Disciplines
ABSTRACT
Damage to agricultural plants and forests by diseases and pests
Mogilev 2010
The concept of epiphytoties
Forest pests and diseases
Pests of agricultural plants
The concept of epiphytoties
Infectious plant diseases differ significantly from each other not only in the characteristics of pathogenesis and external manifestation, but also in the nature of their development in nature. Some diseases are ubiquitous but rare and their incidence rates remain the same. Other diseases are more common, but also little subject to fluctuation; Mass development of these diseases over large areas and severe damage to plants, posing a threat to crops or plantings, are not observed. Such diseases include many types of stem rot of tree species, damping off of seedlings and a number of other diseases.
At the same time, there are diseases whose distribution and development in a certain area or within the entire range is inconsistent and subject to sharp fluctuations. These include many types of rust and powdery mildew, some types of vascular diseases and root rot of tree species, a number of viral and other diseases.
Mass development infectious disease of plants in a certain area for a certain period of time is called epiphytoty. The study of epiphytoties is occupied by a special section of phytopathology - epiphytotiology. This is the study of the development of pathogen populations within host populations of plant diseases arising as a result of their interaction under the influence environment or human intervention.
The role of the pathogen, host plant and environment in the development of epiphytoties
The emergence, development and attenuation of epiphytoties, as well as the dynamics of diseases in general, obey certain patterns and depend on the interaction of three components involved in the epiphytotic process: the pathogen population, the disease, the host plant population and the environment. If this interaction turns out to be favorable for the development of the disease, it progresses and epiphytoty occurs. If, during the course of epiphytoty, conditions are created that prevent its further development, its gradual attenuation occurs, and the outbreak of the disease stops. Each of these components plays a specific role and is equally important.
The role of the pathogen. The role of the pathogen is extremely important. For epiphytoties to occur, it is necessary that the pathogen be highly aggressive and virulent in relation to the host plant growing in the area and that the reservoir of infection be sufficiently large. The decisive prerequisite for epiphytoties may be the emergence of a highly aggressive pathogen new to the area, which has high fertility and the ability to accumulate in nature.
The higher the rate of reproduction of a pathogen, the easier and faster it spreads, the longer it can survive without losing viability, the greater the threat of epiphytoties. And, conversely, a reduction in the supply of infection, a decrease in the reproductive energy and speed of spread of the pathogen, and a decrease in its aggressiveness are the most important prerequisites for the attenuation of epiphytoties.
The role of the host plant. It is also very significant. Mass development of the disease occurs only if many susceptible plants are concentrated in a certain area. The importance of this factor increases when the development cycle of the pathogen occurs on two different feeding plants, as is observed in rust fungi of different hosts. In this case, for epiphytoty to occur, the presence of both host plants in sufficient quantities is necessary. Therefore, removal of the intermediate host may be a decisive condition for stopping further development of rust.
They play a very important role in the accumulation of infection and the development of epiphytoties. weeds, on which pathogens of cultivated plants and forest species can multiply and persist. The role of the host plant during introduction is especially great: if the introduced plant species turns out to be susceptible to local pathogens, then over time the development of these diseases on the new host can acquire the character of epiphytoties. The same thing happens if a pathogen enters new areas and finds new susceptible hosts there.
The host plant can also play an important role in the attenuation of epiphytoties. If epiphytoty is seasonal, then its attenuation can be facilitated by age-related changes in plants or their tissues, due to which the plants acquire resistance, as is observed, for example, with lodging of seedlings or powdery mildew of oak.
A factor in the attenuation of epiphytoties may also be a general increase in the stability of plantings under the influence of changes in external conditions or as a result of natural selection, since the most stable or hardy individuals survive in the population. Finally, epiphytoty can stop when resistant species or forms of plants are introduced into the culture.
The role of the environment. This role often turns out to be decisive. Especially great importance have climatic conditions of the area and weather conditions of a given year, sometimes several recent years. The determining factor in this case is, as a rule, not one factor (for example, optimal temperature or humidity), but the optimal combination of many factors that favor the mass reproduction of the pathogen, its accumulation and spread, and infection of plants. Environmental factors can contribute to the occurrence of epiphytoties even if they have an adverse effect on the host plant, causing it to weaken and thereby reducing its resistance to the disease. And, conversely, any conditions that prevent the accelerated reproduction and persistence of the pathogen in nature, its rapid spread and infection of plants, as well as all factors that increase the viability and resistance of the host plant, can be factors in the attenuation of epiphytoties.
Thus, epiphytoty is a complex complex of interrelated elements that continuously change under the influence of many factors: genetic, environmental, economic, etc. These elements form a kind of continuous chain in time and space, and its individual links and the nature of the connections between them are determined by the specific relationships in the pathogen-host system and the characteristics of the environment.
Dynamics of epiphytoties
Epiphytoty is a dynamic process, in the development of which a number of sequential stages are distinguished: 1) the preparatory stage, or pre-epiphytoty; 2) an outbreak of disease, or epiphytoty itself; 3) stage of depression, or attenuation of epiphytoties.
During the first stage, those changes in the populations of the pathogen and the host plant occur in nature, which then lead to an outbreak of the disease: the emergence of new, more aggressive races of the pathogen or more active, due to optimal weather conditions, reproduction and accumulation of the pathogen already existing in the area , concentration on large areas of susceptible plants (for example, when creating pure forest crops) or reducing the sustainability of plantings for one reason or another; the emergence of favorable conditions for plant infection (for example, due to human economic activity, increased recreational loads or the influence of abiotic factors, etc.). The duration of this stage may vary, but most often it lasts several years.
The second stage (outbreak) is characterized by simultaneous damage to a large number of plants, a severe degree of damage and death of a significant part of the diseased plants, and a high level of damage caused by the disease. The moment of culmination of the outbreak can be confined to a certain age of plants or to a period with the most favorable weather conditions for the development of the disease.
During the third stage (depression), there is a gradual decrease in the number of diseased plants and the degree of their damage. Usually the zone of distribution of epiphytoties also decreases.
The duration of epiphytoties, as well as its individual stages, depends on many factors and can vary greatly. The epiphytoty of some diseases develops within one season, while others can last for many years.
Processes occurring in interacting populations of pathogens and host plants are described and explained by mathematical models. Mathematical modeling of epiphytoties is considered in the works of Van der Planck and other authors. Models of population changes over time are used to analyze population parameters, assess development and predict epiphytoties.
Types of epiphytoties
Depending on the characteristics of development and the scale of distribution in nature, the following main types of epiphytoties are distinguished:
Local epiphytoties, or enphytoties. They are characterized by the annual (over several years) strong development of the disease in a limited area, sometimes in the form of separate foci. Pathogens of local epiphytoties, as a rule, are constantly present in a given area. They can survive for a long time in the soil, on plant debris, seeds, weeds, etc. The infectious origin of such pathogens usually accumulates slowly in nature and spreads relatively slowly. However, if the infection reserve reaches a high level, then in the presence of susceptible plants and favorable external conditions, epiphytoties often occur. An example of local epiphytoty is the enphytoty of lodging of seedlings, observed annually in nurseries in many regions of the country.
Progressive epiphytoties. Epiphytoties of this type begin as local ones, but over time cover larger areas. They are usually caused by the most aggressive pathogens that have high reproductive energy, form several generations of asexual sporulation during the summer and are able to quickly spread through the air or with the help of insects (for example, epiphytoty of rust, powdery mildew, some vascular and viral diseases).
The cause of progressive epiphytoties may be the transfer of infected planting material from one area to another or the entry of the pathogen into new areas where there are significant areas of susceptible host plants. An example of such an epiphytoty is the epiphytoty of Weymouth pine blister rust, which arose and quickly covered the vast areas occupied by this pine in the United States after the causative agent of the disease was brought to America from Europe.
Progressive epiphytoties often develop over many years. In young pine crops created on vast areas of concentrated clearings in the northern and northwestern regions of Russia, progressive epiphytoties of snow shutter and rust of pine shoots are observed.
Widespread epiphytoties, or panphytoties, are characterized by the massive development of the disease over the territory of an entire country, sometimes several countries or continents. Panphytotia is a rather rare phenomenon, but they can take on the dimensions of a national disaster, as happened during the panphytotia of potato late blight in the mid-19th century. At the beginning of the 20th century. The character of a panphytotia was the massive spread of oak powdery mildew and gooseberry powdery mildew, brought from America to Europe. The widespread distribution of root fungus in many countries of Europe and North America over the past decades has also reached the level of panphytotia.
In addition, a distinction is made between slowly developing, or tardive, and rapidly developing, or explosive, epiphytoties. The former are most often observed when perennial plants (for example, trees) are affected by diseases such as Dutch elm disease or root fungus on conifers. They are characterized by a smooth progression of the outbreak and its gradual attenuation. The latter are caused mainly by pathogens with a high reproduction rate and are characterized by a sharp increase in the outbreak and its rapid attenuation. The course of epiphytoties of this type is often subject to seasonal changes and is largely determined by environmental factors. Examples include epiphytoty of apple scab, lodging of seedlings, powdery mildew, rust, schutte, etc.
Knowledge of the characteristics of various types of epiphytoties allows us to predict their occurrence, the course of further development, and use this data to make more accurate forecasts and plan forest protection measures.
Forest pests and diseases
Sometimes trees become victims of other living creatures: rodents, insects, fungi and bacteria. Under natural conditions, as a rule, such phenomena generally do not harm the forest, but human intervention often provokes an imbalance, especially if the anthropogenic impact is superimposed on an unfavorable season for the forest (drought, hurricane) and a sharp increase in the number of certain species of living organisms.
Rodents
Even in beautiful and well-groomed areas in winter, trees can suffer from mice and even hares looking for food and therefore gnawing on the bark. Traps, repellents and special events will help you avoid problems.
Insects
Insects, primarily beetles, are funny and useful under normal conditions (for example, they destroy dead trees), but when a number of unfavorable factors are applied, they can pose a serious problem for the forest. Beetles occupy a special place among all animals. There are a lot of them: in terms of the number of species, the order of beetles is the largest not only in the insect class, but in the entire animal kingdom. We actually live on Planet Bug - more than a quarter of all animal species on Earth are bugs.
Some varieties of these insects have been annoying owners of beautiful forest areas for many years now. Among them, the most dangerous are the insidious bark beetles (Scolytidae). Bark beetles are a relatively small family in the order Coleoptera. The vast majority of members of the family are highly specialized insect feeders, inhabitants of the living part of the bark of woody plants or wood. It is necessary to note, first of all, the typograph bark beetle (Ips typographus), the engraver (common - Pityogenes chalcographus, four-toothed - Pityogenes quadridens), pine beetle (large spruce - Dendroctonus micans, large pine - Tomicus piniperda, small pine - Tomicus minor). The pine subbark mite (family Pyemotidae) is also occasionally found in young coniferous forests.
Depending on the nature of the weakening factor, the death of trees due to the settlement of stem pests can be single, group (focal) and continuous. Depending on this, methods of combating beetles may vary.
Fungi and bacteria
Currently, the forests of the Moscow region are greatly weakened by anthropogenic factors and unfavorable meteorological conditions: hurricanes, summer droughts, alternating long and short winters, winters with large and small amounts of snow, sharp frosts. Trees are under severe stress, so pathogenic fungi and bacteria become overly active, presenting a large-scale problem that every site owner should be aware of. Conifers are especially hard hit: spruce and pine. These huge trees are very sensitive and in many areas of the Moscow region they are infected with tar cancer (seryanka).
Pests of agricultural plants
Pests of agricultural plants, animals, damaging cultivated plants or causing their death. The damage caused by plant pests and diseases is high: according to the Food and Agriculture Organization (FAO) of the United Nations, global losses annually amount to approximately 20-25% of the world's potential food crop yield. Among vertebrates there are many V. s. R. in the class of mammals, especially in the order of rodents. Of the invertebrate animals of agriculture. plants damage some species of gastropods; a significant number of roundworms from the class of nematodes (see Nematode plant diseases). The most diverse and numerous types of V. s. r., belonging to the type of arthropod animals: the class of insects, the class of arachnids (mites), some species from the class of millipedes and crustaceans (woodlice).
The greatest damage to crops is caused by insects, which is explained primarily by their biological characteristics, abundance of species, high fertility and speed of reproduction. Harmful to Agriculture insects are classified according to a systematic principle (by orders) and by the nature of their diet. Herbivorous insects and mites are divided into polyphagous, or polyphagous, feeding on plants of different families; oligophages, or limited eaters, feeding on plants of different species of the same family; monophages, or monovores, - mainly plants of one species. Polyphagous pests cause great damage to the harvest of various crops: locusts, some crickets (for example, mole crickets); from beetles - click beetles, darkling beetles and others; among butterflies - the winter cutworm and related species of gnawing cutworms, stem moths, gamma cutworms, etc. There are numerous limited-eating insects, which include the Swedish fly, the green-eyed fly, the Hessian fly, the kuzka bread beetle and many others that feed exclusively on cereal plants. Nodule weevils, pea codling moths, pea aphids and others damage legume plants. There are very diverse types of insects that feed on cruciferous plants - cabbage whites, cabbage moths, cruciferous flea beetles, cabbage flies, etc. Of the monovores, phylloxera is very harmful, damaging the grapevine, pea weevil - peas, clover weevil - clover, etc. Harmful insects and mites are also classified according to the groups of crops they damage - pests of cereals, pests of vegetable crops, etc., which is convenient for practical purposes.
There are two main types of plant damage; the first is characteristic of insects with gnawing, the second with piercing-sucking mouthparts. Gnawing insects eat plants roughly or partially from the edges of leaves, skeletonize leaves, gnaw parenchyma, etc., gnaw or partially gnaw leaves, stems and shoots, eat through passages, mine leaves and stems, gnaw bast, cambium and wood under the bark, etc. e. Piercing-sucking insects, for example, aphids, bugs, etc., before feeding, introduce secretions of the salivary glands into plants, the enzymes of which cause a number of biochemical changes. Often one or another V. s. R. in their nutrition they are confined to certain plant organs. Hence the groups of pests of roots, stems, leaves, buds, flowers, fruits, etc. An important species feature of V. s. R. There is also, to one degree or another, pronounced selectivity in relation to the age and physiological state of the damaged plant organ. Thus, aphids prefer to feed on young tissues, the cherry slimy sawfly on adult tissues, etc.
Distribution of V. s. R. and the formation of a complex of species in certain agrobiocenoses are directly dependent on changing environmental conditions and the ecological plasticity of species. Each species is characterized by a specific territory it occupies. There are a general range of the species, zones of harmfulness and habitats. The range of a species is the territory in which it occurs. Natural, or primary, habitats are created as a result of the independent dispersal of a species; their boundaries are determined mainly by climatic conditions, the location of large mountain ranges, seas, the presence of plants suitable for food, and other factors. Artificial, or secondary, insects enter habitats along with seeds, planting material, etc. Secondary habitats are characteristic, for example, of grape phylloxera, Comstock scale insects, and many other pests brought to the USSR. The harmful zone is the part of the general range in which a particular species occurs most consistently in the greatest numbers and where it is most harmful. Stations, or habitats, are areas with certain environmental conditions favorable for a given species. But for the same type of V. s. R. in different natural areas stations may be different. It depends on where a given species finds its ecological optimum. For example, the June Khrushchev in the steppe lives mainly on fallow lands and virgin lands, in Central Asia- on shaded and humidified areas garden plots. In a number of species (locusts, aphids, etc.) annual and seasonal changes in habitats are observed.
Temperature conditions are of great importance for the development and reproduction of insects and mites. Each species is characterized by a certain temperature regime at which all life processes occur most intensively. Large deviations from the optimum often cause the death of the pest. The ability of insects to tolerate long-term cooling varies not only among individual species, but even among one species, depending on its physiological state. Knowing the sum of average daily effective temperatures, it is possible to establish (signal) the approximate dates of appearance and predict the duration of individual phases of insect development and the number of generations per season. For insects whose development is associated with the soil, its chemical composition, acidity, physical structure, aeration and humidity are essential. By influencing these factors using agricultural techniques (soil cultivation, fertilization, etc.), it is possible to significantly change conditions in a direction unfavorable for harmful insects. For example, liming of acidic soils worsens the breeding conditions for many species of click beetles. Among other factors, the reproduction of pests is significantly influenced by the interaction of V. with. R. with other animal organisms. In a biocenosis, complex “food chains” develop, which have a great influence on the relationships between the components inhabiting a particular biotope. For example, various species of aphids feed on plant sap, and the sugars they secrete serve as food for ants, ichneumon wasps, and some flies. Many species of predatory insects feed on aphids, such as beetles and coccinellid larvae, chrysopus larvae, and hoverfly larvae. Aphids and their enemies - insects of prey - are eaten by a variety of insectivorous birds, which, in turn, become victims of birds of prey. A disruption in some part of the established “food chains” leads in some cases to a significant and unforeseen or undesirable change in the biocenosis as a whole.
Systematic change by man in the process of agriculture. production of biotope conditions causes a corresponding restructuring of biocenological connections and the structure of the biocenosis. So-called secondary biotopes and agrobiocenoses are formed. For example, as a result of the plowing of virgin lands in the Eastern USSR and the replacement of various types steppe plants cultivated cereals with their characteristic agricultural technology, sharp changes occurred in the species composition and number of insects. On the one hand, some monovorous species that previously fed on virgin soil-specific plants died, which caused a depletion of the species composition of the entomofauna in the new cultural biotope; on the other hand, some insect species that previously lived on wild cereals moved to wheat crops, where they found an abundance of more nutritious feed. This, to a certain extent, explains the rapid increase in the number of wheat thrips and gray fall armyworm. Anticipating and regulating such changes is the most important scientific and practical task.
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The main cause of diseases in agricultural plants are pathogens - fungi, bacteria, viruses, as well as some factors external environment- unfavorable soil conditions, low or high air and soil temperatures, etc.
Fungal diseases. Phytopathogenic fungi - causative agents of infectious plant diseases - belong to lower plants. They lack chlorophyll and feed on organic matter. The vegetative body of the fungus (mycelium, mycelium) penetrates the thickness of the leaf or bark with its thin, branching threads (hyphae) and feeds on the juices of the host plant.
Mushrooms are spread by spores or pieces of mycelium by the wind, insects, raindrops, etc. Spores, compacted mycelium-sclerotia or mycelium overwinter. The causative agents of fungal diseases enter the site with planting material, soil, and plant residues. Infection occurs through wounds, natural openings (stomata, for example) or through the cuticle. Diseases are spread by wind, rain, insects, and contaminated seeds. For the development of fungi, high relative air humidity and an optimal temperature of 20 to 28 0 C are required.
Symptoms of diseases are very diverse, but most of them can be reduced to the following main types: wilt (fusarium), spotting (ascochyta blight, anthracnose), formation of pustules similar to pads (stem rust), destruction of individual organs (dusty and hard smut of grain crops, blister smut corn, rot (wet, dry), growth formation (cabbage clubroot), mummification (fruit rot), formation powdery plaque on leaves (powdery mildew), etc.
In some cases, infected plants release dangerous toxins, which, when accumulated in the crop, can cause poisoning to humans and animals.
Bacterial diseases. Bacteria - causative agents of bacterial diseases - single-celled organisms that reproduce by cell division. They, like mushrooms, lack chlorophyll and use ready-made nutrients for their development. Each bacterium consists of one microscopic sized cell. Bacteria that infect plants are in most cases rod-shaped. When unfavorable conditions occur, they can turn into a spore resistant to external conditions. External symptoms of plants affected by bacteria manifest themselves in the form of drying out (black leg, vascular bacteriosis), the appearance of spots (brown spot of beans), and rot (ring rot, rot). Bacterial damage to the vascular system leads to plant wilting. Infection occurs through mechanical damage and stomata. Bacteria overwinter with plant residues, in the soil or on the surface of seeds.
Viral diseases. Viruses are tiny organisms that live and reproduce only in the cells of living organisms. Causes disturbances in plants physiological processes. Viral diseases are introduced mainly with infected planting material. Transmitted from one plant to another by plant sap. Carriers can be aphids, ticks, and bedbugs. Transmission of viral infection also occurs during vegetative propagation of plants (with tubers, root crops, bulbs, seeds). Diseased plants have characteristic features, manifested in changes in color and normal shape affected organs, the appearance of necrosis (dying tissue). The leaves appear mosaic (variegated color), deformation (wrinkling), and yellowness are noted. The most harmful include viral diseases of potatoes (wrinkled and speckled mosaic), mosaic of peas, wheat, sugar beets, and tobacco.
Mycoplasma diseases (dwarfing of corn, jaundice of beets, “witches’ brooms” on trees, greening of strawberry petals, overgrowth of apple trees, etc.) are caused by organisms (mycoplasmas) that have a cellular structure, but the cell does not have a nucleus, and the cell membrane is replaced by a membrane. Diseases are transmitted by vaccinations and insect vectors.
Based on the reasons that cause them, plant diseases are usually divided into two groups: infectious and non-infectious.
The most important damaging abiotic factors include excess and lack of water in the soil and air; soil and air temperature; soil texture and acidity; its contamination and provision of nutrients (macroelements N, P, K and microelements Ca, Fe, Zn, B, Mg, etc.); damaging atmospheric phenomena (showers, lightning, hail, hurricane). Diseases associated with the use of pesticides are called Iatrogenic. These factors cause such widespread and harmful consequences as suffocation of potato tubers, soaking or freezing of winter grains, freezing of wood fruit trees, death of flowers and fruits from spring frosts, reduction in crop yields due to insufficient or unbalanced nutrients and many others. The most common negative effect of the complex is abiotic factors(false potato cancer, enzymatic-mycotic grain drainage, spot necrosis of cabbage, etc.), although a single factor (usually temperature, amount of moisture) can have a limiting effect on the yield and its quality. Diagnosis of non-infectious diseases is quite complex and labor-intensive, often determined by the level of qualifications of the worker and is based mainly on agrochemical research methods or express analyzes using special equipment.
The main feature of infectious diseases is contagiousness, i.e. ability to be transmitted from plant to plant.
It is customary to distinguish several types of specialization (Popkova, 2005).
A plant disease is a violation of various life processes - respiration, evaporation, assimilation, etc. Depending on the causes, diseases are divided into non-infectious (non-contagious) and infectious (infectious).
Non-contagious diseases include diseases associated with unfavorable climatic and soil conditions (lack or excess nutrients, heat, moisture) or with mechanical damage to plants: breakages, hail damage, etc. With these non-contagious diseases, the color of the leaves changes, various spots appear, the plants wither, and the bark cracks. Often, when the causes of non-communicable diseases are eliminated, their symptoms gradually disappear.
Infectious diseases are caused by living organisms: fungi, bacteria, viruses, as well as mycoplasma organisms. They can be transmitted from plant to plant. With local damage, the disease manifests itself in the form of various spots, rot, abnormal tissue growth, and death of the bark. In case of a general disease, when the pathogen spreads throughout vascular system, the plant withers. The cause of the disease can be determined by external signs and microscopic analysis.
Fungi and bacteria enter plant tissue through damage caused by insects, hail, during processing by machines, as well as through natural openings: nectaries of flowers, stomata of leaves. Fungi can penetrate into intact tissues, dissolving the outer covers of plants with special enzymes. Fungi and bacteria are carried by wind, raindrops, insects, birds, and humans. Viruses enter the plant through wounds and are transmitted only through the sap of a diseased plant in contact with healthy ones or during pruning, harvesting, as well as piercing-sucking insects - aphids, bugs, cicadas.
Diseases of fruit and berry crops. Powdery mildew of apple trees is widespread mainly in the southern regions. In nurseries, it sometimes damages up to 100% of seedlings. This disease is caused by a fungus. It appears in early spring in the form of a white powdery coating on inflorescences, leaves and shoots. Such inflorescences do not form fruits, the leaves begin to fall off prematurely, the growth of the affected shoots slows down, and their tops dry out. In affected trees, winter hardiness is greatly reduced, and yields drop by 20–80%. The fungal disease apple and pear scab is common in areas with big amount precipitation falling in summer and especially in spring. Spots with a greenish-black velvety coating appear on the leaves, the leaves dry out and fall off prematurely. On fruits, the flesh cracks under dry, leathery spots, and the fruit often takes on an irregular shape. Black cancer affects leaves, fruits, trunk bark and skeletal branches. Damage to the bark is especially dangerous, since branches die above the diseased area. If the lesion envelops the trunk in a ring, the entire tree dies.
Black currants and gooseberries are affected by a fungal disease - powdery mildew. Especially dangerous disease- terryness of black currant. Its causative agent, a mycoplasma organism, is transmitted with cuttings taken from a diseased plant, and is also carried by the currant bud mite. Affected plants stop bearing fruit and have to be destroyed. The leaves of diseased plants become three-lobed, with coarse veins, and without the typical currant smell. They are smaller than healthy ones and noticeably elongated lengthwise. The flower becomes double (the calyx, corolla and stamens turn into narrow purple outgrowths).
The most harmful disease of strawberries is gray rot. In wet years, it sometimes kills more than half the crop.
Diseases vegetable crops. Clubroot attacks cabbage, turnips, rutabaga, radishes and other plants from the cabbage family, including weeds - cress, shepherd's purse, etc. In the affected plants, nodules (growths) of various sizes form on the roots. Such plants are stunted in growth and their leaves wilt in the hottest part of the day.
Late blight of tomatoes, caused by the late blight fungus, affects the fruits, leaves and stems in the form of brown spots. Most often, fruits become diseased; in wet years, up to 60–80% of the crop dies. Usually the disease spreads to tomatoes from potatoes, where the fungus infects the tops and tubers.
A very dangerous disease is potato cancer. The fungus infects tubers and stolons, less often - stems. Large (first white, then turning brown and rotting) growths form on the affected tubers. The causative agent of the disease persists in the soil for a long time.
In the southern regions, anthracnose, or copperhead, of pumpkins is common.
Bacteriosis of cucumbers affects leaves (angular brown spots) and fruits, which become covered with sores and, as a rule, take a hook-shaped form.
Diseases of field crops. Diseases caused by various types smut mushrooms. They damage individual grains, whole ears, leaves and leaf sheaths, turning them into a black mass of spores (hard and dwarf smut of wheat, dusty smut of wheat, barley and oats, stem smut of wheat, rye, etc.). Rust fungi are no less harmful; some of them require an intermediate host (barberry, buckthorn, etc.) for normal development. By affecting almost all above-ground plant organs, rust pathogens lead to the formation of puny, incomplete grains, which greatly reduces the yield. The most harmful are stem rust of cereals, brown leaf rust of wheat and rye, yellow rust of cereals, crown rust of oats, etc. Winter crops suffer greatly from powdery mildew, snow mold, and root rot.
Measures to combat diseases of agricultural plants. To combat diseases, as well as pests, agrotechnical, physical-mechanical, chemical and biological methods are used: plants are sprayed with special preparations (chemical and biological) designed to combat fungi and bacteria, destroy plant debris, weeds and intermediate hosts, use healthy seed and planting material, observe optimal sowing times and crop rotation, apply fertilizers, use disease-resistant varieties, treat seeds, etc.
MINISTRY OF EDUCATION OF THE REPUBLIC OF BELARUS
EE "Mogilev State University"
them. A.A. Kuleshova"
Department of Physics and Technical Disciplines
ABSTRACT
Damage to agricultural plants and forests by diseases and pests
Mogilev 2010
The concept of epiphytoties
Forest pests and diseases
Pests of agricultural plants
The concept of epiphytoties
Infectious plant diseases differ significantly from each other not only in the characteristics of pathogenesis and external manifestation, but also in the nature of their development in nature. Some diseases are ubiquitous but rare and their incidence rates remain the same. Other diseases are more common, but also little subject to fluctuation; Mass development of these diseases over large areas and severe damage to plants, posing a threat to crops or plantings, are not observed. Such diseases include many types of stem rot of tree species, damping off of seedlings and a number of other diseases.
At the same time, there are diseases whose distribution and development in a certain area or within the entire range is inconsistent and subject to sharp fluctuations. These include many types of rust and powdery mildew, some types of vascular diseases and root rot of tree species, a number of viral and other diseases.
The massive development of an infectious plant disease in a certain area over a certain period of time is called epiphytoty. The study of epiphytoties is occupied by a special section of phytopathology - epiphytotiology. This is the study of the development of pathogen populations within host populations of plant diseases that arise as a result of their interaction under the influence of the environment or human intervention.
The role of the pathogen, host plant and environment in the development of epiphytoties
The emergence, development and attenuation of epiphytoties, as well as the dynamics of diseases in general, obey certain patterns and depend on the interaction of three components involved in the epiphytotic process: the pathogen population, the disease, the host plant population and the environment. If this interaction turns out to be favorable for the development of the disease, it progresses and epiphytoty occurs. If, during the course of epiphytoty, conditions are created that prevent its further development, its gradual attenuation occurs, and the outbreak of the disease stops. Each of these components plays a specific role and is equally important.
The role of the pathogen. The role of the pathogen is extremely important. For epiphytoties to occur, it is necessary that the pathogen be highly aggressive and virulent in relation to the host plant growing in the area and that the reservoir of infection be sufficiently large. The decisive prerequisite for epiphytoties may be the emergence of a highly aggressive pathogen new to the area, which has high fertility and the ability to accumulate in nature.
The higher the rate of reproduction of a pathogen, the easier and faster it spreads, the longer it can survive without losing viability, the greater the threat of epiphytoties. And, conversely, a reduction in the supply of infection, a decrease in the reproductive energy and speed of spread of the pathogen, and a decrease in its aggressiveness are the most important prerequisites for the attenuation of epiphytoties.
The role of the host plant. It is also very significant. Mass development of the disease occurs only if many susceptible plants are concentrated in a certain area. The importance of this factor increases when the development cycle of the pathogen occurs on two different feeding plants, as is observed in rust fungi of different hosts. In this case, for epiphytoty to occur, the presence of both host plants in sufficient quantities is necessary. Therefore, removal of the intermediate host may be a decisive condition for stopping further development of rust.
Weeds play a very important role in the accumulation of infection and the development of epiphytoties, on which pathogens of diseases of cultivated plants and forest species can multiply and persist. The role of the host plant during introduction is especially great: if the introduced plant species turns out to be susceptible to local pathogens, then over time the development of these diseases on the new host can acquire the character of epiphytoties. The same thing happens if a pathogen enters new areas and finds new susceptible hosts there.
The host plant can also play an important role in the attenuation of epiphytoties. If epiphytoty is seasonal, then its attenuation can be facilitated by age-related changes in plants or their tissues, due to which the plants acquire resistance, as is observed, for example, with lodging of seedlings or powdery mildew of oak.
A factor in the attenuation of epiphytoties may also be a general increase in the stability of plantings under the influence of changes in external conditions or as a result of natural selection, since the most stable or hardy individuals survive in the population. Finally, epiphytoty can stop when resistant species or forms of plants are introduced into the culture.
The role of the environment. This role often turns out to be decisive. The climatic conditions of the area and the weather conditions of a given year, sometimes of the last few years, are especially important. The determining factor in this case is, as a rule, not one factor (for example, optimal temperature or humidity), but the optimal combination of many factors that favor the mass reproduction of the pathogen, its accumulation and spread, and infection of plants. Environmental factors can contribute to the occurrence of epiphytoties even if they have an adverse effect on the host plant, causing it to weaken and thereby reducing its resistance to the disease. And, conversely, any conditions that prevent the accelerated reproduction and persistence of the pathogen in nature, its rapid spread and infection of plants, as well as all factors that increase the viability and resistance of the host plant, can be factors in the attenuation of epiphytoties.
Thus, epiphytoty is a complex complex of interrelated elements that continuously change under the influence of many factors: genetic, environmental, economic, etc. These elements form a kind of continuous chain in time and space, and its individual links and the nature of the connections between them are determined by the specific relationships in the pathogen-host system and the characteristics of the environment.
Dynamics of epiphytoties
Epiphytoty is a dynamic process, in the development of which a number of sequential stages are distinguished: 1) the preparatory stage, or pre-epiphytoty; 2) an outbreak of disease, or epiphytoty itself; 3) stage of depression, or attenuation of epiphytoties.
During the first stage, those changes in the populations of the pathogen and the host plant occur in nature, which then lead to an outbreak of the disease: the emergence of new, more aggressive races of the pathogen or more active, due to optimal weather conditions, reproduction and accumulation of the pathogen already existing in the area , concentration on large areas of susceptible plants (for example, when creating pure forest crops) or reducing the sustainability of plantings for one reason or another; the emergence of favorable conditions for plant infection (for example, due to human economic activity, increased recreational loads or the influence of abiotic factors, etc.). The duration of this stage may vary, but most often it lasts several years.
The second stage (outbreak) is characterized by simultaneous damage to a large number of plants, a severe degree of damage and death of a significant part of the diseased plants, and a high level of damage caused by the disease. The moment of culmination of the outbreak can be confined to a certain age of plants or to a period with the most favorable weather conditions for the development of the disease.
During the third stage (depression), there is a gradual decrease in the number of diseased plants and the degree of their damage. Usually the zone of distribution of epiphytoties also decreases.
The duration of epiphytoties, as well as its individual stages, depends on many factors and can vary greatly. The epiphytoty of some diseases develops within one season, while others can last for many years.
Processes occurring in interacting populations of pathogens and host plants are described and explained by mathematical models. Mathematical modeling of epiphytoties is considered in the works of Van der Planck and other authors. Models of population changes over time are used to analyze population parameters, assess development and predict epiphytoties.
Types of epiphytoties
Depending on the characteristics of development and the scale of distribution in nature, the following main types of epiphytoties are distinguished:
Local epiphytoties, or enphytoties. They are characterized by the annual (over several years) strong development of the disease in a limited area, sometimes in the form of separate foci. Pathogens of local epiphytoties, as a rule, are constantly present in a given area. They can survive for a long time in the soil, on plant debris, seeds, weeds, etc. The infectious origin of such pathogens usually accumulates slowly in nature and spreads relatively slowly. However, if the infection reserve reaches a high level, then in the presence of susceptible plants and favorable external conditions, epiphytoties often occur. An example of local epiphytoty is the enphytoty of lodging of seedlings, observed annually in nurseries in many regions of the country.
Progressive epiphytoties. Epiphytoties of this type begin as local ones, but over time cover larger areas. They are usually caused by the most aggressive pathogens that have high reproductive energy, form several generations of asexual sporulation during the summer and are able to quickly spread through the air or with the help of insects (for example, epiphytoty of rust, powdery mildew, some vascular and viral diseases).
The cause of progressive epiphytoties may be the transfer of infected planting material from one area to another or the entry of the pathogen into new areas where there are significant areas of susceptible host plants. An example of such an epiphytoty is the epiphytoty of Weymouth pine blister rust, which arose and quickly covered the vast areas occupied by this pine in the United States after the causative agent of the disease was brought to America from Europe.
Progressive epiphytoties often develop over many years. In young pine crops created on vast areas of concentrated clearings in the northern and northwestern regions of Russia, progressive epiphytoties of snow shutter and rust of pine shoots are observed.
Widespread epiphytoties, or panphytoties, are characterized by the massive development of the disease over the territory of an entire country, sometimes several countries or continents. Panphytotia is a rather rare phenomenon, but they can take on the dimensions of a national disaster, as happened during the panphytotia of potato late blight in the mid-19th century. At the beginning of the 20th century. The character of a panphytotia was the massive spread of oak powdery mildew and gooseberry powdery mildew, brought from America to Europe. The widespread distribution of root fungus in many countries of Europe and North America over the past decades has also reached the level of panphytotia.
In addition, a distinction is made between slowly developing, or tardive, and rapidly developing, or explosive, epiphytoties. The former are most often observed when perennial plants (for example, trees) are affected by diseases such as Dutch elm disease or root fungus on conifers. They are characterized by a smooth progression of the outbreak and its gradual attenuation. The latter are caused mainly by pathogens with a high reproduction rate and are characterized by a sharp increase in the outbreak and its rapid attenuation. The course of epiphytoties of this type is often subject to seasonal changes and is largely determined by environmental factors. Examples include epiphytoty of apple scab, lodging of seedlings, powdery mildew, rust, schutte and other agricultural use Law >> Ecology
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