Plant Protection

a branch of agricultural science that devises ways and means of controlling diseases, pests, and weeds of crops and trees, as well as a set of measures used in agriculture and forestry to prevent and eliminate the damage done to plants by harmful organisms.

The goal of plant protection is not only to destroy harmful organisms or limit their activity but also to forecast the time they appear and the possible extent to which they might spread, as well as to prevent especially harmful organisms from moving from some countries and regions to others. Plant protection is based on the data obtained by several agronomic (agriculture, plant growing, selection, agricultural chemistry, agricultural physics, agricultural plant pathology, and entomology), zoological, and botanical (principally taxonomy, anatomy, morphology, ecology, plant and animal geography) disciplines; genetics; biochemistry; and plant and animal biochemistry and physiology. Plant protection is closely related to such sciences as meteorology and climatology; chemistry and physics, which provide the scientific basis of chemical and biophysical control methods; and hygiene and toxicology, which study the direct and indirect effects of pesticides on plants and animals.

Every year the damage done to crops by pests and diseases, according to data of the United Nations Food and Agricultural Organization (FAO), constitutes approximately 20–25 percent of the potential world yield of food crops. Therefore, plant protection plays an extremely important role in increasing the production of agricultural crops and in protecting them.

It was known in very ancient times that diseases and pests are harmful to plants. Eor example, there are references in Assyrian cuneiform inscriptions and in Egyptian frescoes (third millennium B.C.) to the devastating attacks of desert locusts. Ancient Greek and Roman writers describe rusts, smuts, tree cancer, and other diseases, which were regarded as a manifestation of “god’s wrath.” Early in the 18th century attempts were made to classify plant diseases (by the French botanist J. de Tournefort). In the late 18th century many experiments demonstrated the contagiousness of a large number of diseases (A. T. Bolotov in Russia, M. Tillet in France, F. Fontana in Italy, J. Fabricius in Denmark). In the latter half of the 19th century the German scientist H. A. De Bary, the Russian scientist M. S. Voronin, and others discovered new species of phytopathogenic fungi and studied their morphology and developmental characteristics. Works of a generalizing nature concerning harmful insects also appeared in the 19th century. The tremendous damage done to the economy of many countries in the latter half of the 19th century by pests and diseases (including phylloxera, locusts, and potato blight) made it necessary to centralize research efforts and the ways of devising control measures. Entomology and plant pathology government bureaus, departments, and administrations were established in a number of countries, and scientific research was organized. In the United States the position of staff entomologist was set up in 1853, and entomological stations appeared in 1888.

In Russia the standing Odessa and Kharkov entomological committees were organized at the end of the 1870’s and in the early 1880’s. The position of provincial entomologist was set up in 1887 for the first time, and in 1894 the Bureau of Entomology was established in the Department of Agriculture. The bureau was directed by I. A. Porchinskii, who did much to organize plant protection in the country. In 1904 entomological stations appeared in Kiev, Voronezh, Kharkov, Stavropol’, Tashkent, and elsewhere, and entomology sections were organized in some agricultural experiment stations. The Central Plant Pathology Station of the St. Petersburg Botanical Garden carried out research from 1903 to 1907. In 1907 the Department of Agriculture established the Bureau of Mycology and Plant Pathology. By 1916, 30 organizations in Russia were engaged in activities related to plant protection.

By the early 20th century, thousands of new species of phytopathogenic fungi, bacteria, viruses, and nematodes had been discovered (the Russian scientists A. A. lachevskii, D. I. Ivanovskii, I. L. Serbinov, and G. K. Burgvits; the American scientists E. Smith and W. Stanley), and the species composition of the principal pests and their biology and physiology were being studied. Research in plant pathology and entomology was based on the principles and methods of ecology and biocenology. Methods of controlling harmful organisms were improved. Agrotechnical, biological, chemical, biophysical, and other control methods, including those involving direct extermination of harmful organisms as well as indirect actions through environmental factors, plant hosts, or a complex of other organisms associated with the development of pests or other pathogens, were devised. Such Rus-sian scientists as N. M. Kulagin and N. V. Kurdiumov were the first to advocate the principle of comprehensive differentiated use of methods of plant protection and, above all, preventive methods, which generally are the most effective.

The agrotechnical method of plant protection is based on the use of general and specific farming practices to create ecological conditions unfavorable to the development and reproduction of harmful organisms and helpful in increasing the capacity of plants to protect themselves. This method was used for the first time early in the 20th century by the Russian entomologist N. V. Kurdiumov. Its development was furthered by the work of the Russian scientists A. A. lachevskii, A. I. Borggardt, T. D. Strakhov, and V. N. Shchegolev; the German scientists P. Zorauer and G. Gassner; the American scientists G. Keitt and R. Sprague; and the Swiss scientist E. Gäumann. Correct crop rotations was considered a very important measure because the continuous cultivation of any annual plant results in the concentration of pests and causative agents of diseases. Their numbers can also frequently be reduced by appropriate methods of cultivating the soil. For example, shallow afterharvest plowing of the stubble field followed by late fall plowing help to destroy the causative agents of many diseases and wintering insect pests. Plowing and cultivation promote the activity of predatory insects (ground beetles, for example) that destroy pests living in the soil. The sorting and cleaning of seeds, growing of healthy planting stock, prompt culling of inferior or diseased plants, removal of crop residues, and control of weeds are of great value. Planting crops at the optimal times helps to prevent the vulnerable phases of plant development from coinciding with the periods of maximum activity of pests. The addition of fertilizer promotes plant growth and increases resistance to injuries. The decisive factor in controlling many pests, such as the stink bug (Eurygaster integriceps) on wheat, is early harvesting and, in case of swath harvesting, the shortest possible interval between hay mowing time and harvesting windrows. Using the best techniques of caring for plants greatly increases the effectiveness of all the measures taken to treat diseases and exterminate pests.

Breeding and growing resistant cultivated plant varieties is one of the most important methods of controlling pests and diseases. Major contributions to the study of plant immunity have been made by N. I. Vavilov, A. A. lachevskii, P. G. Chesnokov, I. D. Shapiro, and T. I. Fedotova (USSR); J. Eriksson (Sweden); E. Stakman (USA); and D. Carbone and C. Arnaudi (Italy). After the creation of the first cotton and cowpea varieties resistant to fusarium wilt (USA), thousands of diverse crop varieties were bred in many countries, often with combined resistance to several diseases and pests. In the USSR, for example, breeders developed potato varieties resistant to cancer and late blight; a sunflower variety resistant to rust, broomrape, and sunflower moth; and wheat, tobacco, and other plant varieties with combined resistance to a number of diseases and pests.

The biological method of plant protection is based on the use of predatory and parasitic insects (entomophages), predatory mites (acariphages), microorganisms, nematodes, birds, mammals, and so forth to suppress or reduce the numbers of harmful organisms. The first successful attempts to employ beneficial insects were made in China (predatory insects to combat caterpillars and other pests). In 1855 the American entomologist A. Fitch tried to acclimatize one of the parasites of the wheat midge in the USA. More vigorous and extensive research began at the end of the 19th century. In the United States the following entomophages were im-ported from other countries and acclimatized: the Rodolia ladybug (1888) was brought to California from Australia to control the cottony-cushion scale and the beetle Cryptolaemus montrouzieri (1892) to control the mealybug; entomophages of the gypsy moth were imported from Europe and Japan in the early 20th century. A total of 115 of 520 imported entomophages were acclimatized in the United States by 1970. The development of the biological method in the USA is associated with the names of such scientists as S. E. Flanders, C. P. Clausen, and F. J. Simmonds. Similar work is being done in Canada. Research in this field was initiated in Russia in 1879 by I. I. Mechnikov, who used a fungus, the causative agent of green muscardine, to combat granary weevil and beet pest(Bothynoderes punctiventris). The studies of I. M. Krasil’shchik, I. A. Porchinskii, I. V. Vasil’ev, N. V. Kurdiumov, I. la. Shevyrev, V. P. Pospelov, and N. A. Teleng were important.

The methods of using parasites and predators of pests in the USSR are varied. The introduction and acclimatization of entomophages that limit their numbers in the countries of origin are effective in controlling pests brought in from other countries. For example, the predaceous Rodolia a ladybug imported (1931) from Australia helped to eradicate foci of the cottonycushion scale; the parasitic chalcid fly imported (1926, 1930) from the USA was effective in controlling the woolly apple aphid. Seasonal colonization is the way local species of entomophages are used. Among the local species that are raised in special biological laboratories and then released over the crops are the egg parasite Trichogramma against cutworms, tortricids, and silkworm moths; the beetle Cryptolaemus montrouzieri against mealybugs on citrus trees and grape vines;Pseudaphycusmalinus against the Comstock mealybug; and the predaceous mite Phytoseulius persimilis against spider mites in hothouses.

In some countries, crop pests are controlled by pathogenic fungi, bacteria, and viruses. The USSR started (1962) the production of the bacterial preparation entobacterin (made from spores and protein crystals of Bacillus thuringiensis var. galleriae), which is effective against a number of leaf miners. The fungal preparation beauverin (made from spores of Beaveria Bassiana orB. globulifera) combined with pesticides is used against the Colorado potato beetle and other pests. Other preparations are now under study. Methods are being devised to accumulate the nuclear polyhedrosis virus against the gypsy and pine moths and cabbage moth and granulosis virus against the turnip and grain moths and other pests. In the USA viral preparations are used to control cutworms, Colias erate, pine sawfly, gypsy moth, and the like. Biological methods are also being devised to control plant diseases and weeds. Cases of secondary parasitism are common in nature, for example, fungi on fungi that cause plant diseases. The imperfect fungus Tuberculinapersicina and others are frequently parasitic on rust fungi, andCicinnobolus cesatii is parasitic on Erysiphales. The biological preparation trichodermin, derived (1962) from the soil saprophytic fungus-antagonist Trichoderma, sup-presses the causative agents of diseases of flax and cereal grains and cotton wilt when it is applied to the soil. Considerable progress has been made in some countries in using antibiotics to control plant diseases. Herbivorous insects are imported and acclimatized to control weeds brought in from other countries. For example, the noxious weed cactus opuntia was destroyed over large areas of Australia in the 1950’s by introducing the cactus moth from America. In the United States the leaf beetle Chrysolina quadrigemina and the borer Agrilus hyperici were used to destroy Klamath weed and the like. In the USSR efforts are under way to naturalize enemies of the noxious ragweed (Ambrosia) imported from Americaand of Russian sweet sultan that migrated from Central Asia. In the USSR microbiological methods are used to control rats and mouselike rodents by artificially infecting them with pathogenic microbes that cause fatal epizootics. The myxomatosis virus is used in Australia to control rabbits.

The chemical method of plant protection is based on the use of substances that are toxic to harmful organisms. A number of chemical compounds began to be widely used after 1945 because of their marked effectiveness, universality, and simplicity of use. A special industry was created in many countries to manufacture pesticides, and there were several thousand kinds by 1970. In the 1920’s and 1930’s mostly arsenic compounds and several other chemical preparations highly toxic to man and warm-blooded animals were used as insecticides. They were replaced beginning in 1945 by synthetic organic compounds such as DDT and lindane and in the 1960’s by organophosphorus and chlorine- and nitrogen-containing compounds with selective action. The selectivity of pesticides is based on the study of the physiological processes, for example, metamorphosis, which are specific to the insect organism. Preparations that exert an effect on insects that is similar to the one produced by their specific hormones—for example, molting and juvenile hormones— are beginning to find practical application. Mercury disinfectants of seeds and planting stock have been replaced by new and safe compounds. The scale on which copper-containing preparations were once used is now reduced. Dozens of herbicides made from various classes of chemical compounds can control weeds in almost all crops.

The extensive and one-sided use of pesticides in many countries has had some undesirable consequences: pollution of the soil and natural water, appearance of pests resistant to pesticides, accumulation of pesticides in food products, and so forth. Hence, steps are being taken all over the world to limit the use of pesticides, for example, establishment of maximum permissible levels of pesticide residues in food products and determination of the latest possible times for chemical treatment. In the USSR, the use of diene compounds (aldrin and dieldrin), almost all arsenic preparations, DDT, and some others is forbidden. Safe preparations are being sought along with better methods of applying them (spraying of extremely small quantities that minimize pollution of the ecosystem; preplanting treatment of seeds and planting stock that is least dangerous to entomophages and pollinators). The use of pesticides is strictly regulated by the State Committee for Chemical Means of Controlling Pests, Plant Diseases, and Weeds, which is under the jurisdiction of the Ministry of Agriculture of the USSR. The development of chemical methods of plant protection is associated with such names as R. D. O’Brien, J. G. Horsfall, and R. L. Metcalf (USA); E. Y. Spencer (Canada); H. Martin (Great Britain); G. Unterstenhófer (Federal Republic of Germany); and G. D. Ugriumov, A. N. Nesmeianov, and A. M. Il’inskii (USSR).

The mechanical methods of plant protection (use of barrier and trap ditches, sticky strips, various devices to catch pests) that once played an important role are now little used because they require much labor and are not very effective.

Recent advances in biology, physics, and chemistry are opening up new opportunities in the search for better methods of plant protection. In the USA, USSR, Czechoslovakia, and other countries the biophysical method based on the use of such physical agents as radioactive and thermal emissions, ultrasound, and light is being intensively developed. Gamma radiation is used to sterilize insects and obtain strains of microorganisms with increased virulence (for biological control), and various sources of light are used to trap insects and signal their appearance in nature. Self-destruction methods resulting in the rapid and frequently complete extermination of harmful insect species are of widespread interest. These methods are based on artificial breeding and release of sterile or genetically defective races of pests, chiefly males, that produce infertile offspring after mating with nonsterile individuals. Sterilization is accomplished by means of gamma radiation, certain chemical compounds (specifically, antimetabolites and alkylating compounds), antibiotics, and sometimes exposure to heat. This method was used on the island of Curaçao in the Caribbean and in the USA (Florida, Georgia, and Alabama over an area of 17.5 million hectares) to destroy the dangerous cattle parasite, the fly Callitroga hominivorax. In the USSR research is under way on the sterilization of the codling moth, turnip moth, boll worm, pea and bean weevils, granary weevil, and other pests. Food and sex attractants and various types of repellents are under study.

In the late 1940’s the discovery of the adverse effects of the chemical method intensified interest in so-called integrated plant protection by which is meant, in the narrow sense, a combination of chemical and biological methods to preserve useful entomophages as much as possible and, in the broader sense, a rational combining of all methods to construct differentiated systems of protective measures. The ultimate objective of integrated plant protection is the gradual substitution of biological methods for pesticides, regulation of the use of pesticides, and finding chemical agents with selective action. This approach is widely used in Canada and the USA (mainly in California) to protect fruits, some field crops, vegetables, and alfalfa.

In the USSR the Main Administration of Plant Protection of the Ministry of Agriculture, the Forest Preservation and Protection Section of the USSR State Committee for Forestry, analogous administrations in the ministries of agriculture and many forestry ministries of the Union republics, and a large network of plant protection stations direct the practical work involved in plant protection. Scientific methods centers for plant protection include the All-Union Institute of Plant Protection (Leningrad) and the corresponding department of the V. I. Lenin Academy of Agricultural Sciences (Moscow). Research is also carried out by the Azerbaijan, Armenian, All-Russian, Georgian, Kazakh, and Ukrainian scientific re-search institutes of plant protection; Institute of Biological Methods of Plant Protection (Kishinev); many forest research institutes; branch institutes;agricultural and forestry institutes and academies; universities; and experiment and breeding stations. Various institutes of the Academy of Sciences of the USSR, research organizations of the Ministry of the Chemical Industry of the USSR, and the Ministry of Public Health of the USSR also make important contributions. Studies on scientific and practical problems in plant protection are published in the transactions of the academies and institutes and in Zashchita rastenii (Plant Protection), Khimiia pestitsidov (Chemistry of Pesticides), Lesnoe khoziaistvo (Forestry), and many other journals. By the 1970’s personnel were being trained in 18 agricultural and many forestry schools, where there are departments or divisions of plant or forest protection, and in many agricultural and forestry technicums.

In the United States the largest organizations concerned with plant protection are the entomological department of the agricultural research center in the city of Beltsville, the laboratory for cereal grain pests of the coastal plains experiment station in the city of Tifton, the western research center for the study of cotton pests, and the research center for the study of insects injurious to fruit trees in the city of Yakima. There is an antilocust research center in Great Britain and a national institute of agricultural research with a network of stations in France. The socialist countries also have large plant protection institutes: in Poznan (Poland), Klein Machnow (German Democratic Republic [GDR]), Sofia (Bulgaria), and Budapest (Hungary). There are entomological institutes in Czechoslovakia and the GDR.

The USSR subscribes to the International Plant Protection Convention, which was adopted by more than 30 countries; the European and Mediterranean Plant Protection Organization; the agreement on cooperation in quarantines and on plant protection against pests and diseases signed, in addition to the USSR, by Albania, Bulgaria, Hungary, the GDR, the Peoples’ Republic of China, Poland, Rumania, and Czecho-slovakia; and many bilateral conventions. International congresses on plant protection and international plant pathology and entomology congresses are held from time to time.