Methods of biological plant protection, Principles...

Methods of Biological Plant Protection

In a broad sense, biological protection of plants implies the entire system of protection not associated with the use of chemistry, namely: field sanitation, mandatory crop rotations, seed infection analysis and seed recovery, biological control, the use of natural and synthetic elicitors (inducers of plant protective responses) . In a narrow sense, biological protection includes only the last two methods - the use of antagonists, parasites and predators of phytopathogenic organisms and their metabolites.

Principles of organic farming

Many farmers in Europe and in America use organic farming principles for growing plants, which include the following methods of management:

- use only organic fertilizers;

- possible reduction of soil treatments;

- abandoning pesticides;

- Mandatory crop rotation.

The use of organic fertilizers only is possible only when the entire structure of animal husbandry is changed. Organic fertilizers are introduced into the soil in much larger volumes than mineral fertilizers, so transporting them for considerable distances will require considerable financial and energy costs, so the cost of transportation will exceed the cost of the material itself. Therefore, the huge farms in which a large number of livestock are grown, and which are therefore located far apart, should be replaced by small ones, but often located. By the way, this method will protect animals from infectious diseases, because the death of animals on a small locally located farm will bring much less losses than on a large farm.

Reducing soil tillage will have a beneficial effect on its structure and protect against dust storms, but it will create additional problems in plant protection, as many insect pests and resting mushroom structures, weed seeds, are wintering in the soil. Soil cultivation, especially autumn plowing, causes many of them to die. The abandonment of autumn plowing on virgin lands cultivated under wheat in the 60-70s. XX century. in the USSR led to the mass reproduction of grain scoops and large losses from its harvest. Deep plowing with the turnover of the reservoir reduces the reserves of causative organisms root rot by 10-15 times and the reserves of septoria fungi and seeds of weed plants - 5-10 times. On the other hand, inter-row processing causes damage to rootlets through which wound parasites are introduced, and on irrigated lands - and the formation of a hard sole is lower than the depth of embedding of the working organs, after which the death of the roots occurs.

Failure of pesticides. Dutch phytopathologist A. van Bruggen analyzed a large literature devoted to the study of the severity of diseases of field crops, and concluded that not all crops can avoid significant crop losses without the use of fungicides. Ego is possible when growing cereals (wheat, barley, rice) and sugar beet, but in years favorable for the development of late blight , it is impossible to obtain a satisfactory potato crop without the use of fungicides. So, to protect against some diseases, there are no alternatives to fungicides yet. However, the reduction in the number of chemical treatments can be achieved using relatively resistant varieties and the following sanitary measures.

Seed quality control. Many pathogens are transmitted exclusively or almost exclusively with planting material - seeds, bulbs, tubers, etc. For example, in the tubers of potatoes pathogens of late blight, many bacterial and all viral diseases, in cabbage seeds the causative agent of alnteriosis, etc., are preserved. Analysis of seed infection and selection for sowing and planting only healthy batches can significantly reduce the index X 0 and delay the onset of epiphytoty.

In addition to many traditional methods of analyzing seeds for their infection, more and more sensitive methods are now increasingly being used: the placement of seeds on selective media in which only a small group of interesting fungi and bacteria can be developed; molecular methods, including multiplex PCR methods, with the help of which it is possible to determine the presence of several types of pathogens in the seed material (see Chapter 5). The presence of viruses can be visualized almost exclusively by molecular methods (analysis of viral proteins by immunochemical methods and nucleic acids by PCR methods). If the planting material is completely infected with viruses, it can be improved in special laboratories where virus-free plants from an isolated meristem are obtained (in the meristem cells viruses are usually not contained) and grow them on an artificial nutrient medium.

Field sanitation. An important role in reducing the indicator X 0 is the harvesting of plant remains - roots, stems, leaves, fruits, on which many pathogens are preserved.

Use of natural plant toxicants. Previously, it was said that many plant species have antibiotic substances, but they have not found wide application in plant protection. However, it is possible to use chemical compounds not isolated from plants, but whole plants. For example, cabbage (cruciferous) plants form toxic glyconolates in cells (see Chapter 2). If the seeds of radish (varietal or wild) and the grown green plants are plowed into the soil, then it is possible to improve the site from the stock of infection of fungi, bacteria and nematodes for subsequent sowing. Presowing treatment of seeds with flour or paste from cabbage seeds will protect seedlings from root rot.

Rotations are absolutely necessary to reduce damage from plant diseases. Their sacrifice to a young man named "agro-economic zoning of territories" led to the terrible results described in Ch. 3. The crop rotation, first, kills wintering in the soil stocks of infection of specialized parasites that can not affect the culture that is replacing them. For example, the causative agent of white rot of sunflower fungus Sclerotinia sclerodorum hibernates in the form of sclerotia in the soil. Sowing for three years barley frees the soil from sclerotia. The introduction of beans (lucerne, clover, lupine, pea), potatoes or winter rapeseed reduces the incidence of root wheat by a factor of five to six in the cereal crop rotation and reduces the empty-colony by 9-10 times. Secondly, the crop rotation spatially spreads the fields sown with the same crop, which prevents the transfer of the infection from its origin. In any case, rotations reduce X 0 .

Biological control is a large rapidly growing set of technologies (see paragraph 4.3.2).

Thus, organic farming is quite possible under certain conditions. Why, in spite of the propaganda of healthy food, only a small percentage of farmers use it on their farms? Because, despite all efforts, the refusal of mineral fertilizers and pesticides leads to a decrease in labor productivity, a decrease in yield and a deterioration in the external appearance of the produce (for example, a higher percentage of apples with spots of scab and fodder moves). The governments of a number of countries and the market are trying to compensate for the farmers' losses at a higher price for products grown without the use of chemicals, but so far this is not enough. However, intensive research, especially in the field of plant biological protection, allows us to hope that an alternative to chemical plant protection will be found.

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