The article presents corn diseases that manifest themselves at the initial stages of seedlings, germination, growth and development of the crop.
Corn seed mold disease during germination
Corn disease manifests itself on seeds contained in the soil. Its symptoms are characterized by the appearance of plaque of various colors on the surface of the seeds, characteristic of certain types of fungi. The disease is caused by saprotrophic micromycetes. For example, the development of fungi from the genera Penicillium Link, Aspergillus Micheli, Mucor Micheli, Botrytis Micheli and others leads to the formation of gray-green mold. Dark mold is caused by fungi of the genera Cladosporium Link, Alternaria Nees, etc., and pink mold is caused by fungi of the genera Trichothecium Link, Sporotrichum Link and others.
Grains in which the seed coat is damaged or affected by pathogens of other diseases become moldy especially quickly. Conditions characterized by a decrease in soil temperature (cooling) after sowing seeds contribute to their damage.
Diseased corn seeds do not form seedlings, and in humid conditions they are completely covered with abundant mycelium of the pathogen. Seeds in which the embryo is not infected germinate late, forming weak seedlings that are often unable to reach the soil surface and die before reaching its surface. Young plants grown from slightly damaged seeds are weakened, stunted, and somewhat chlorotic. 
The causative agents of this corn disease are Fusarium spp. The development of the disease is possible in the presence of a seed infection (latent, since heavily affected seeds are discarded at the stage of preparing the seed material), pathogens in the soil and under the influence of favorable abiotic environmental factors for the development of the disease. Among the latter are low temperatures during seed germination, violations of seed placement depth, and increased crop density.
Brown spot, or helminthosporium blight of corn
Symptoms of this disease in corn can be found on the leaves, underground and aboveground internodes, and on the ears of the plant. At the same time, according to our observations, leaves are most intensively affected. The development of the disease begins on the lower leaves and gradually covers the upper ones. During its diagnosis, it is important to take into account the following typical symptoms: on the affected leaves, small whitish spots (which then turn brown) first appear along the leaf blade with a narrow dark brown or reddish-brown border, in the center of which a brownish-olive coating forms. Subsequently, the affected areas increase in size, often merge and cover almost the entire leaf blade, causing it to dry out and die. Often the size of the spots reaches a length of about 25 cm or more. On cobs, the disease can appear at their base and in the depressions between the rows of grains in the form of a thick dark brown felt coating.
The harm of brown spot is the premature death of leaves, which leads to a decrease not only in grain yield, but also in green mass. Severely affected plants are susceptible to infection by stem rot pathogens.
The causative agent of the disease is the fungus Exserohilum turcicum (Pass.) Leonardet Suggs (synonyms - Bipolaris turcica (Pass.) Shoemaker, Helminthosporium turcicum (Pass.), Drechslera turcica (Pass.). It is characterized by high variability of pathogenic properties and the presence of races.
The corn disease, as a rule, develops under conditions of sufficient and excessive moisture, heavy dew, the presence of water on the leaf surface for 6-18 hours and elevated temperatures (23 ... 30 ° C) and an optimal relative air humidity of more than 90%. Late corn crops are more severely affected. The incubation period of the disease depends on the age of the plant and the condition of the leaf surface. On young plants it lasts up to seven days, and on adults - up to 11 days. Sporulation is intensively carried out at 100% relative air humidity. Poor, poorly fertilized soils increase the susceptibility of corn to brown spot.
Typically, on the soil surface and at a depth of 10 cm, the fungus is preserved in plant debris in the form of a mycelium, which produces new conidial sporulation in the spring. It dies in the soil at a depth of 20 cm. The pathogen may be retained by conidia on the surface of the seeds.
Corn disease: rust
The disease usually appears on corn leaves in the second half of the plant's growing season. At the beginning of the disease, inconspicuous light yellow spots appear on the leaves, on which brownish oblong (up to 1 mm) urediniopustules (they contain urediniospores) are then formed, which are covered for quite a long time by the epidermis. They are placed randomly on the leaves of corn. Over time, the epidermis ruptures, the pustules are exposed, and a spore mass is released and spreads. By the end of the corn growing season, instead of urediniopustules, black teliopustules appear, which contain teliospores. With severe development of the disease, the leaves dry out prematurely, and underdeveloped heads of cabbage with flat grains are formed.
The causative agent of the disease is the dioecious fungus Puccinia sorghi Schw. On corn plants it forms uredinio- and teliopustules. Intermediate life-giving agents for the fungus are wood sorrel (Oxalis spp.), weeds that are common in corn crops in the southern regions of Ukraine.
Favorable conditions for the development of the disease are moderate temperature, high relative humidity, frequent precipitation and heavy dew. The incubation period lasts five to eight days. The source of corn rust infection is mainly urediniospores, which in the southern regions overwinter well on leaf debris in the field. The role of teliospores in the preservation of the pathogen in winter and the restoration of infection is small.
Measures to combat corn diseases
Measures to protect corn from diseases should be based on the cultivation of resistant hybrids, timely implementation of agrotechnical practices that provide the best conditions for growth and development (observance of crop rotation, favorable sowing dates and optimal plant density, as well as provision of balanced fertilizer). For sowing, you should use high-quality seeds treated with approved disinfectants. If necessary, fungicides are used during the growing season of plants. You should also comply with the requirements regarding the optimal timing of harvesting and high-quality seed processing. 
Disinfection of seeds allows you to control pathogens located on its surface (for example, the causative agent of flying smut) and inside (causative agents of Fusarium, red rot, etc.), as well as protect against mold in the soil during germination.
To treat seeds, disinfectants approved in Ukraine are used. The “List of Pesticides and Agrochemicals Permitted for Use in Ukraine” contains a wide range of preparations based on various active ingredients:
Alios, TN (triticonazole, 300 g/l), 1.0-2.0 l/t (against mold, bubbly and dusty smut, root rot);
Vaxa, KS (carboxin, 375 g/l + thiramide, 375 g/l), 2.0 l/t (against root and stem rot, loose smut);
Viking, v.s.k. (Carboxin, 200 g/l + thiram, 200 g/l), 2.5-3.0 l/t (against flying and blister smut, root and stem rot, molding of seeds);
Vispar, KS (carboxin, 375 g/l + thiram, 375 g/l), 2.0 l/t (against root and stem rot, loose smut);
Vitavax 200 FF, v.s.k. (Carboxin, 200 g/l + thiram, 200 g/l), 2.5-3.0 l/t (against flying and blister smut, root and stem rot, molding of seeds);
Granivit, TN (carboxin, 200 g/l + thiram, 200 g/l), 2.5-3.0 l/t (against flying and bubbly smut, root and stem rot, molding of seeds);
Inshur Perform, t.k.s. (Triticonazole, 80 g/l + pyraclostrobin, 40 g/l), 0.5 l/t (against mold, blister and loose smut, root rot);
Maxim Quatro 382.5 FS, TN (thiabendazole, 300 g/l + azoxystrobin, 15 g/l + fludioxonil, 37.5 g/l), 1.0-1.5 l/t or 8.5 ml per 50 000 seeds (root rot, flying and blister smut, molding of seeds);
Maxim 025 FS, TN (fludioxonil, 25 g/l), 1.0 l/t (red rot, fusarium, pythium rot, seed mold);
Maxim XL 035 FS, tk.s. (Fludioxonil, 25 g/l + metalaxyl-M, 10 g/l), 1.0 l/t (against root and stem rot, molding of seeds);
Royalflo, v.s.k. (Tirami, 480 g/l), 2.5-3.0 l/t (against root and stem rot, molding of seeds);
Stamina, TN (pyraclostrobin, 200 g/l), 0.25 l/t (against rhizoctonia, pythium, fusarium, seed mold);
TMTD, KS (thiram, 400 g/l), 3.0-4.0 l/t (against root and stem rot, seed mold, smut);
Fever 300 FS, TN (prothioconazole, 300 g/l), 0.6-0.9 l/t (against loose smut and root rot);
Fluosan, t.k.s. (thiram, 533 g/l), 3.0 l/t (against seed mold, root and stem rot, blister smut) and other approved drugs.
Systematic monitoring during the growing season of plants makes it possible to timely identify the onset of the development of dangerous diseases and make the right decision regarding the use of fungicides.
Abacus, mk.e. (pyraclostrobin, 62.5 g/l + epoxiconazole, 62.5 g/l), 1.5-1.75 l/ha (against fusarium, rust and helminthosporium);
Acanto plus 28, KS (picoxystrobin, 200 g/l + cyproconazole, 80 g/l), 0.75-1.0 l/ha (against helminthosporium and rust);
Amistar Extra 280 SC, KS (azoxystrobin, 200 g/l + cyproconazole, 80 g/l), 0.5-0.75 l/ha (against fusarium, helminthosporiosis, grain mold, rust, loose smut);
Coronet 300 SC, KS (tebuconazole, 200 g/l + trifloxystrobin, 100 g/l), 0.6-0.8 l/ha (against rust and helminthosporium);
Custodia, KS (tebuconazole, 200 g/l + azoxystrobin, 120 g/l), 1.0-1.2 l/ha (against helminthosporiosis, rust, fusarium);
Retengo, EC (pyraclostrobin, 200 g/l), 0.5 l/ha (against fusarium, rust and helminthosporium), etc.
When using chemical protective agents, you should adhere to the spraying periods recommended by the manufacturers of the drugs and the regulations for their use.
M. Pikovsky, Ph.D. biol. sciences,
M. Kirik, dr. biol. sciences,
A. Stolyar, Ph.D. agricultural sciences,
NUBiP of Ukraine
Citation information
“The very first” diseases of corn / M. Pikovsky, M. Kirik, A. Stolyar // Proposition / - 2017. - No. 4. - P. 128-130
The article presents corn diseases that manifest themselves in the initial stages of crop growth and development.
Seed molding during germination
The disease manifests itself on seeds contained in the soil. Its symptoms are characterized by the appearance of plaque of various colors on the surface of the seeds, characteristic of certain types of fungi. The disease is caused by saprotrophic micromycetes. For example, the development of fungi from the genera Penicillium Link, Aspergillus Micheli, Mucor Micheli, Botrytis Micheli and others leads to the formation of gray-green mold. Dark mold is caused by fungi of the genera Cladosporium Link, Alternaria Nees, etc., and pink mold is caused by fungi of the genera Trichothecium Link, Sporotrichum Link and others.
Grains in which the seed coat is damaged or affected by pathogens of other diseases become moldy especially quickly. Conditions characterized by a decrease in soil temperature (cooling) after sowing seeds contribute to their damage.
Fusarium disease of seeds and seedlings
Diseased seeds do not form seedlings, and in humid conditions they are completely covered with abundant mycelium of the pathogen. Seeds in which the embryo is not infected germinate late, forming weak seedlings that are often unable to reach the soil surface and die before reaching its surface. Young plants grown from slightly damaged seeds are weakened, stunted, and somewhat chlorotic.
The causative agents of the disease are Fusarium spp. The development of the disease is possible in the presence of a seed infection (latent, since heavily affected seeds are discarded at the stage of preparing the seed material), pathogens in the soil and under the influence of favorable abiotic environmental factors for the development of the disease. Among the latter are low temperatures during seed germination, violations of seed placement depth, and increased crop density.
Brown spot, or helminthosporium
Symptoms of the disease can be found on leaves, underground and aboveground internodes, as well as on the ears of plants. At the same time, according to our observations, leaves are most intensively affected. The development of the disease begins on the lower leaves and gradually covers the upper ones. During its diagnosis, it is important to take into account the following typical symptoms: on the affected leaves, small whitish spots (which then turn brown) first appear along the leaf blade with a narrow dark brown or reddish-brown border, in the center of which a brownish-olive coating forms. Subsequently, the affected areas increase in size, often merge and cover almost the entire leaf blade, causing it to dry out and die. Often the size of the spots reaches a length of about 25 cm or more. On cobs, the disease can appear at their base and in the depressions between the rows of grains in the form of a thick dark brown felt coating.
Symptoms of brown spot on corn leaves
The harm of brown spot is the premature death of leaves, which leads to a decrease not only in grain yield, but also in green mass. Severely affected plants are susceptible to infection by stem rot pathogens.
The causative agent of the disease is the fungus Exserohilum turcicum (Pass.) Leonardet Suggs (synonyms - Bipolaris turcica (Pass.) Shoemaker, Helminthosporium turcicum (Pass.), Drechslera turcica (Pass.). It is characterized by high variability of pathogenic properties and the presence of races.
The disease, as a rule, develops under conditions of sufficient and excessive moisture, heavy dew, the presence of water on the leaf surface for 6-18 hours and elevated temperatures (23 ... 30 ° C) and an optimal relative humidity of more than 90%. Late corn crops are more severely affected. The incubation period of the disease depends on the age of the plant and the condition of the leaf surface. On young plants it lasts up to seven days, and on adults - up to 11 days. Sporulation is intensively carried out at 100% relative air humidity. Poor, poorly fertilized soils increase the susceptibility of corn to brown spot.
Typically, on the soil surface and at a depth of 10 cm, the fungus is preserved in plant debris in the form of a mycelium, which produces new conidial sporulation in the spring. It dies in the soil at a depth of 20 cm. The pathogen may be retained by conidia on the surface of the seeds.
Rust
The disease usually appears on leaves in the second half of the plant's growing season. At the beginning of the disease, inconspicuous light yellow spots appear on the leaves, on which brownish oblong (up to 1 mm) urediniopustules (they contain urediniospores) are then formed, which are covered for quite a long time by the epidermis. They are placed randomly on the leaves of corn. Over time, the epidermis ruptures, the pustules are exposed, and a spore mass is released and spreads. By the end of the corn growing season, instead of urediniopustules, black teliopustules appear, which contain teliospores. With severe development of the disease, the leaves dry out prematurely, and underdeveloped heads of cabbage with flat grains are formed.
Signs of rust on corn leaves
The causative agent of the disease is the dioecious fungus Puccinia sorghi Schw. On corn plants it forms uredinio- and teliopustules. Intermediate life-giving agents for the fungus are wood sorrel (Oxalis spp.), weeds that are common in corn crops in the southern regions of Ukraine.
Favorable conditions for the development of the disease are moderate temperature, high relative humidity, frequent precipitation and heavy dew. The incubation period lasts five to eight days. The source of corn rust infection is mainly urediniospores, which in the southern regions overwinter well on leaf debris in the field. The role of teliospores in the preservation of the pathogen in winter and the restoration of infection is small.
Control measures for corn diseases
Measures to protect corn from diseases should be based on the cultivation of resistant hybrids, timely implementation of agrotechnical practices that provide the best conditions for growth and development (observance of crop rotation, favorable sowing dates and optimal plant density, as well as provision of balanced fertilizer). For sowing, you should use high-quality seeds treated with approved disinfectants. If necessary, fungicides are used during the growing season of plants. You should also comply with the requirements regarding the optimal timing of harvesting and high-quality seed processing.
Disinfection of seeds allows you to control pathogens located on its surface (for example, the causative agent of flying smut) and inside (causative agents of Fusarium, red rot, etc.), as well as protect against mold in the soil during germination.
To treat seeds, disinfectants approved in Ukraine are used. The “List of Pesticides and Agrochemicals Permitted for Use in Ukraine” contains a wide range of preparations based on various active ingredients:
Alios, TN (triticonazole, 300 g/l), 1.0-2.0 l/t (against mold, bubbly and dusty smut, root rot);
Vaxa, KS (carboxin, 375 g/l + thiramide, 375 g/l), 2.0 l/t (against root and stem rot, loose smut);
Viking, v.s.k. (Carboxin, 200 g/l + thiram, 200 g/l), 2.5-3.0 l/t (against flying and blister smut, root and stem rot, molding of seeds);
Vispar, KS (carboxin, 375 g/l + thiram, 375 g/l), 2.0 l/t (against root and stem rot, loose smut);
Vitavax 200 FF, v.s.k. (Carboxin, 200 g/l + thiram, 200 g/l), 2.5-3.0 l/t (against flying and blister smut, root and stem rot, molding of seeds);
Granivit, TN (carboxin, 200 g/l + thiram, 200 g/l), 2.5-3.0 l/t (against flying and bubbly smut, root and stem rot, molding of seeds);
Inshur Perform, t.k.s. (Triticonazole, 80 g/l + pyraclostrobin, 40 g/l), 0.5 l/t (against mold, blister and loose smut, root rot);
Maxim Quatro 382.5 FS, TN (thiabendazole, 300 g/l + azoxystrobin, 15 g/l + fludioxonil, 37.5 g/l), 1.0-1.5 l/t or 8.5 ml per 50 000 seeds (root rot, flying and blister smut, molding of seeds);
Maxim 025 FS, TN (fludioxonil, 25 g/l), 1.0 l/t (red rot, fusarium, pythium rot, seed mold);
Maxim XL 035 FS, tk.s. (Fludioxonil, 25 g/l + metalaxyl-M, 10 g/l), 1.0 l/t (against root and stem rot, molding of seeds);
Royalflo, v.s.k. (Tirami, 480 g/l), 2.5-3.0 l/t (against root and stem rot, molding of seeds);
Stamina, TN (pyraclostrobin, 200 g/l), 0.25 l/t (against rhizoctonia, pythium, fusarium, seed mold);
TMTD, KS (thiram, 400 g/l), 3.0-4.0 l/t (against root and stem rot, seed mold, smut);
Fever 300 FS, TN (prothioconazole, 300 g/l), 0.6-0.9 l/t (against loose smut and root rot);
Fluosan, t.k.s. (thiram, 533 g/l), 3.0 l/t (against seed mold, root and stem rot, blister smut) and other approved drugs.
Systematic monitoring during the growing season of plants makes it possible to timely identify the onset of the development of dangerous diseases and make the right decision regarding the use of fungicides.
Abacus, mk.e. (pyraclostrobin, 62.5 g/l + epoxiconazole, 62.5 g/l), 1.5-1.75 l/ha (against fusarium, rust and helminthosporium);
Acanto plus 28, KS (picoxystrobin, 200 g/l + cyproconazole, 80 g/l), 0.75-1.0 l/ha (against helminthosporium and rust);
Amistar Extra 280 SC, KS (azoxystrobin, 200 g/l + cyproconazole, 80 g/l), 0.5-0.75 l/ha (against fusarium, helminthosporiosis, grain mold, rust, loose smut);
Coronet 300 SC, KS (tebuconazole, 200 g/l + trifloxystrobin, 100 g/l), 0.6-0.8 l/ha (against rust and helminthosporium);
Custodia, KS (tebuconazole, 200 g/l + azoxystrobin, 120 g/l), 1.0-1.2 l/ha (against helminthosporiosis, rust, fusarium);
Retengo, EC (pyraclostrobin, 200 g/l), 0.5 l/ha (against fusarium, rust and helminthosporium), etc.
When using chemical protective agents, you should adhere to the spraying periods recommended by the manufacturers of the drugs and the regulations for their use.
CORN
Bacterial wilt has not been detected in Russia and is subject to external quarantine. First recorded in the USA and described by Stewart in 1897. Currently, the disease has also been registered in Mexico, South Africa, and Italy.
It first appears on the lower leaves of plants in the form of light green longitudinal dashed spots, which quickly turn yellow and spread along the vein along the blade. Later, streaked yellow spots or stripes appear on the stems and upper leaves. Small droplets of exudate often appear at the sites of lesions. Affected plants develop poorly and then wither and die. Sometimes there is premature ejection of male inflorescences and their whitening. On a cross section of the stem of a diseased plant, yellow mucus is released from the vessels.
Early ripening varieties of sweet corn are particularly affected. With early damage, plant seedlings wither and die. On other varieties, the disease usually appears after the appearance of male inflorescences.
The disease is caused by the bacteria Erwinia stewartii (Smith) Dye (syn. Aplanobacterium stewartii Me. Cull., Bacterium stewartii Sm.). They develop at temperatures of 8-39 and die at 53°.
Typical tracheobacteriosis: bacteria, accumulating in vascular bundles, clog and destroy them, as a result of which plant transpiration sharply decreases.
During the growing season, the pathogen is spread by insects. The source of infection can also be contaminated seeds and unrotted remains of affected plants. With severe development of the disease, the yield shortfall can reach 20-25%.
Bacterial stem rots are caused by three types of bacteria: Pseudomonas holci Kendrick, Pectobacterium carotovora Waldee and Erwinia dissolvens Burkh. When affected by the bacterium Ps. holci usually before throwing out the panicle, blurry cream-colored spots from 1 to 10 cm long with a wide dark burgundy or purple border appear in the upper part of the stem. The tops and middle leaves of the affected plants dry out at the edges, while the lower ones remain green. The internal tissues in the affected areas first take on the appearance of a thick light gray, and later a dark brown mass with an unpleasant, cloying odor. Such plants are sterile. The disease is more common on irrigated lands.
When P. carotova bacteria are infected, the central leaf of the plant wilts, curls and turns yellow, and then the entire plant wilts. Spots do not form on the stems, but a gray, rotting, fetid mass is found inside them. The disease appears more often on corn shoots under irrigated conditions.
E. dissolvens most often infects corn in the first half of the growing season. Sick plants are stunted and their leaves become discolored. Brown, then darkening spots appear on the stems, cob wrappers and leaves, especially at the base of the stem, turning into a rotting soft slimy mass with an unpleasant odor. After some time, the rotten tissue dries out and only the vascular bundles remain visible. At the site of the lesion, the stem breaks and falls to the ground. This disease develops especially intensively at excessive humidity and temperatures of 25-30°. Infection of plants increases when they are damaged by insects and tillage tools.
Sources of infection are predominantly unrotted plant debris, as well as wintering weeds affected by rot.
All rots cause thinning of crops and greatly reduce plant productivity. In addition, lodging of affected crops significantly complicates mechanized harvesting.
The hybrids Dneprovsky 460 MB and Collective 150 TV are relatively resistant to stem and root rot.
Distributed in all corn-growing regions of Russia. It appears during the period of milky ripeness in the upper part of the grains in the form of depressed spots of pale gray color, 2-3 mm in diameter. With a more severe development of the disease, the spots become wrinkled or ulcer-like, with a brownish-yellow color. On plants of white-grain varieties, the spots have a narrow dark gray border, while in yellow-grain varieties it is less pronounced.
The number of affected grains on the cobs usually does not exceed 30-40. They are often placed several in a row closer to the top of the cob. The cobs become infected in the field. The main carrier of the pathogen is the bread bug, in whose body live the bacteria Bacillus mesentericus var. vulgatus Flugge. By damaging the grain shell, the bug introduces bacteria into the wound.
In the second half of summer, bread bugs accumulate on millet and mogar crops, as well as on mice that infest corn crops. From these plants, insect vectors fly to corn during its milky ripeness. Cobs are especially often affected, the tops of which are open or poorly covered with wrappers, which is observed with excess moisture.
The harmfulness of bacteriosis lies in the reduction in the keeping quality of the cobs and their rapid molding, as well as in the deterioration of the seed qualities of the affected grains - underdevelopment, reduction in weight and germination.
Preventive measures against bacteriosis are the removal from the field and burning of all post-harvest residues, followed by deep autumn plowing, as well as the destruction of insect carriers.
White rot was found in Ukraine and the Krasnodar region. It appears on the lower part of the stem in the form of large dark weeping spots with a white fluffy cotton wool-like coating. Dark brown sclerotia about 1 cm in diameter are formed on it, as well as in the middle of the affected stems.
The causative agent of the disease is the marsupial fungus Whetzelinia sclerotiorum Korf. et Dumont. It overwinters in the form of sclerotia, which in the spring, germinating, form a mycelium that penetrates the plant, or apothecia - saucer-shaped bodies on cylindrical legs. In the upper part of the apothecium, bags with sacospores are formed. The bags are cylindrical, colorless, measuring 130-135 x 8-10 microns. Each of them contains 8 elliptical colorless sacspores measuring 7-12 x 4-6 µm. The latter also germinate and infect plants. The disease is especially severe in humid, warm years.
The most typical manifestation of leucorrhoea is the formation of one smooth or angular-winding wide crack, which greatly disfigures the shape of the grain. Ruptures of the seed coat are often observed with the overall normal appearance of the caryopsis and its epidermis. Sometimes the endosperm does not have cracks, but, growing in one place, it protrudes through the cracked seed coat in the form of a wart.
Cracks appear at the beginning of the waxy ripeness of the grains, and towards the end of this ripeness their formation stops.
The cause of the disease is a discrepancy between the intensity of growth in the grain of the epidermis and the seed coat, which occurs as a result of a sharp change from drought to excess moisture.
White cobs practically do not reduce the corn yield, but significantly deteriorate its quality. On affected cobs in the field, and even more often during storage, fusarium and mold fungi intensively develop.
Brown spot (helminthosporiosis)
It is most often found in the Transcarpathian region of Ukraine, Georgia and the Primorsky Territory, where it sometimes causes a significant crop shortage. In some years it appears in the North Caucasus, southern Ukraine, Armenia and the Baltic republics.
Leaves of young and older plants, underground and above-ground parts of stems, less commonly roots, and sometimes cobs are affected. Initially, small whitish and then brown spots with a dark or reddish-brownish border appear on the leaves. In the center the spot is covered with a brownish-olive coating. Over time, the spots increase in size, often merge and cover almost the entire leaf blade, as a result of which they dry out and die.
The disease usually begins on the lower leaves.
Greenish or dark spots of various shapes with a border are formed on underground and aboveground internodes. In this case, the parenchyma of the core is almost not destroyed.
On cobs, helminthosporiosis can appear in the form of a thick dark brown coating at their base and in the recesses between the rows of grains.
The disease develops intensively in conditions of sufficient moisture and elevated temperatures. Late corn crops are more severely affected.
The causative agent of the disease is the imperfect fungus Helminthosporium turcicum Pass. Its mycelium first spreads intercellularly in the parenchyma, and then in the vascular system of the leaves, as a result of which the lesion has the character of leaf tracheomycosis. On the surface of the leaves in places of spots, conidial sporulation of the fungus in the form of tufts is formed. Conidiophores are olive-brown, straight or slightly curved, with three septa up to 150 µm long. Conidia are elongated, fusiform, pointed at the ends, olive, with 5-8 septa and a thickened shell. The size of conidia is 85-110 x 20-24 microns. They germinate in dripping moisture at temperatures from 10 to 38° (optimum 23-30°), infecting plants through the stomata, and occasionally through the epidermis.
The duration of the incubation period depends on the age of the plant and the condition of the leaf surface. On young plants it lasts from 3 to 7, and on older plants it lasts 7-11 days. During the growing season of plants, the fungus can produce 2-3 generations of conidia.
On the soil surface and at a depth of 10 cm, the pathogen persists in the form of a mycelium, on which new conidial sporulation is formed in the spring, spreading to corn crops. It usually dies in soil at a depth of 20 cm. In the form of conidia it can also spread with seeds.
The disease causes a significant shortage of grain and green mass. There are no hybrids or varieties of corn with high resistance to the disease.
Diplodia
Diplodia is common in Georgia. It affects ears, stems, leaf sheaths and leaves. The stems turn brown mainly at the lower internodes, then soften and break. White mycelium often appears under the leaf sheath. In places of browning, point-shaped, initially white, and later black pycnidia are formed, protruding outward from under the epidermis. Brown spots, sometimes with pycnidia, also appear on the affected leaves.
The cobs are covered with a continuous cotton-like coating, spreading to the adjacent wrappers. On the grains, especially near the embryo, inside the stem and on the involucres adjacent to the cob, pycnidia are formed in the form of black, slightly convex dots.
The causative agent of the disease is the imperfect fungus Diplodia zeae Lev. Its pycnidia are round or slightly flattened, blackish-gray, 350-500 µm in diameter. A large number of dark brown oblong straight or slightly bent two- and three-celled pycnospores measuring 13-33 x 3-7 µm are formed in them. The optimal temperature for spore germination is 20°, and for the development of the disease - from 28 to 30°.
Sources of infection are infected seeds and remains of infected plants, on which the pathogen persists for 3-4 years.
Red rot is more often found in fairly humid areas of the North Caucasus and the Far East. It usually appears during the period of milky-waxy ripeness of the grain in the form of a bright pink coating on the top of the cob. The wrappers fit tightly to the cob and acquire a brick-red color. The grains are also painted the same color. They become fragile and are filled with mycelium inside.
The causative agent of the disease is the imperfect fungus Fusarium graminearum Schwabe, which has conidial and marsupial stages. Conidia are fusiform-crescent-shaped, with 3-6 septa, measuring 25-75 x 3-6 µm in mass, whitish-pink, golden-yellow or carmine-purple. Microconidia are usually not formed.
Sporangiophores are 330-1200 µm long, sporangia are round, 110-165 µm in diameter, and sporangiospores are yellow, elliptical, 5.5-9.3 x 4.5-7 µm in size. The fungus develops intensively at excessive or moderate humidity and a temperature of 30-35°, so during storage the cobs are almost not affected. The pathogen persists in the form of mycelium and sporangiespores on plant debris in the field. The infection is practically not transmitted by seeds.
With early damage, the cobs become underdeveloped, the seeds lose their viability and become very moldy during storage.
In the south of Ukraine, grain harvest losses from this rot are small (0.05-0.3%), but in some areas they reach 3-4%.
The causative agent is Zea virus I Storey. The virus is transmitted by leafhoppers.
With severe development of the disease, mosaic streaks and spots appear on leaf sheaths, cob wrappers and stems. The productivity of affected plants is reduced. At the same time, the shortfall in grain yield can reach 5-10%.
Diseases caused by a lack of nutrients in the soil slow down the growth and development of both individual organs and the entire corn plant.
With a lack of nitrogen in the soil, corn leaves turn yellow and die, starting from 
lower ones.
A lack of phosphorus leads to slower root growth, and the leaves become dull in color with a reddish or purple tint.
With a lack of potassium in the soil, yellowing of the tops and edges of first the lower and then the upper leaves is observed. Often the leaves die off completely.
A deficiency of manganese, magnesium, boron and other microelements is characterized by the formation of yellow-green spotting and chloroticness on the leaves.
Distributed in all corn growing areas. It especially often manifests itself under irrigated conditions during the period from the beginning of milk to full ripeness of the grain. Reproductive buds, cobs, leaf sheaths, and stems are affected.
The first signs of the disease are the loosening of the stalk and lower part of the cob stem, as well as the appearance of small black piles of spores at the base of the stem and on the lower grains, clearly visible through a magnifying glass. Later, a black dusty coating forms on the cobs, reproductive buds and leaf sheaths.
Affected stems acquire a dirty gray or bluish tint and become macerated with partial destruction of the parenchyma. Under the affected epidermis, which is easily separated from the phloem, there is a noticeable accumulation of spores in the form of a sooty coating.
With severe damage, the cobs are underdeveloped, their stem is loose, grayish with a blue tint, and often breaks up into separate bundles of fibers. The grains in the affected cobs are usually underdeveloped, dull, slightly grayish, and not densely located.
The causative agent of the disease is the imperfect fungus Nigrospora oryzae Fetch. Its mycelium is loose, grayish, located in the grooves between the rows of caryopses, the conidiophores are pale olive, simple or irregularly branched, with septa, slightly swollen at the top. At the top of the conidiophore, one spherical or elliptical conidia is formed, first translucent and then black, with a thick shell. The diameter of the conidia is 12-15 microns. The fungus is spread by conidia overwintering on plant debris and grain.
More intensive development of nigrospora occurs with sufficient humidity and a temperature of 20-25°, especially in late sowings. The harmfulness of the disease is great. Affected cobs lose their marketable quality and are quickly destroyed by mold fungi during storage. Seeds have reduced germination.
Lodging of seedlings
Lodging of seedlings is of two types and is more often found in areas with sufficient moisture, especially on soils prone to waterlogging and poorly drained. The first type of lesion is characterized first by the blackening of thin fibrous and then large roots; the stem at the root collar turns black. Thinning of the stem and drooping of the plants are also observed. Often, a white coating of mycelium is noticeable in the affected areas.
The causative agents of this type of disease are fungi from the genus Pythium Pring., most often P. debaryanum Hesse. It forms a branched mycelium that penetrates plant tissue. Sporulation is asexual - zoosporangia with zoospores and sexual - oospores. Zoosporangia are ovoid or spherical, 15-26 µm in diameter, oospores are smooth, 12-20 µm.
In addition to corn, the pathogen affects sorghum, wheat, oats and other plants. It is not transmitted with seeds, but is stored on the remains of affected plants in the form of oospores.
The second type of infection is characterized by the appearance of weak shoots with a pale green color. The roots rot, causing the plants to fall out. Often at the base of plant stems there is a faint pink coating with sickle-shaped colorless conidia 8.4-6.0 x 12.4-4.5 µm, with several septa.
The causative agent of this type of disease is the fungus Fusarium moniliforme Scheldon. It persists on seeds and remains of affected plants in the soil.
Lodging of seedlings can cause large thinning of corn crops.
Blackening of vascular bundles was found in the Krasnodar region and in the south of Ukraine. Appears at the beginning of milky ripeness of the grain. The above-ground parts of plants (stems, leaves and leaf sheaths) acquire a red-purple or brown color. The color change begins with the upper leaves and gradually spreads to the lower leaves. Typically on leaves, the red-purple coloration first appears along the central vein and then covers the rest of the blade.
In humid weather, a whitish-pink, delicate, velvety coating appears on the affected vagina. On a cross section of the stem, blackening of the vascular bundles is clearly visible, which is the most characteristic sign of the disease. Often the disease causes excessive thickening of the stem.
The causative agent is the imperfect fungus Serhalosporium acremonium Corda. On its mycelium, vertical, simple, slightly thinned at the top conidiophores 30-60 µm long are formed. At their ends, ovoid unicellular conidia measuring 3-4 x 1-1.5 microns, collected in spherical heads, are successively formed. Plants become infected during the growing season with conidia. The fungus spreads through the vascular system of the stem and often reaches the cobs, where it infects the seeds. When seeds germinate, the mycelium penetrates the sprout and spreads diffusely throughout the plant.
The harmfulness of the disease lies in the fact that plants grown from the affected seeds do not bear fruit. Plants infected before the panicles are thrown out produce puny seeds. When the grain is infected at the beginning of milky ripeness, a significant reduction in yield is not observed.
Rust The causative agent of the disease is the dioecious fungus Puccinia sorghi Schw., which forms uredinia with urediniospores and telia with teliospores (black pustules) on corn. Urediniospores can be spherical or elliptical, pale brown, finely spinous, 21-35 µm in diameter. Teliospores are oblong, club-shaped, dark brown, two-celled, 31-50 x 18-22 µm in size, with a thick and elongated brown stalk. The fungus also has spermogonial and aecial stages, which occur occasionally on sorrel weeds (Oxalis L. spp.), a very common corn weed in the southern regions. However, in most cases, corn is infected by urediniospores, which in the south overwinter well on the remains of infected corn plants in the field. Urediniospores can germinate at temperatures from 4 to 34° (optimum 17-18°) and high air humidity. The incubation period of the disease usually lasts 5-8 days. During the summer period, the fungus can produce 2-3 generations of urediniospores. During the harvesting period, urediniospores fall on the cobs, and together with the seeds, on new corn crops. The role of teliospores in maintaining infection is small. They germinate in the spring, forming basidia with basidiospores. The latter, scattering, can infect kisliki during germination, but in Russia this is observed very rarely. Aeciospores from sour sorrel can only be the primary source of infection of corn. The harmfulness of rust is manifested in the premature drying of leaves, as a result of which the ears are underdeveloped and puny grains are formed in them. Tooth corn varieties have increased resistance to rust, and sweet corn varieties have reduced resistance. Pink mold
Gray rot is common in the southern regions of Ukraine, Rostov and other regions of Russia. It appears at the beginning of the milky-waxy ripeness of the grain in the form of a thick gray coating between the rows of grains. It only affects grain on the cob. First, rot appears in the upper part of the cob, and then quickly spreads to the lower part. Affected grains turn brown, die and crumble easily.
Rust is more common in Transcaucasia, on the Black Sea coast of the Caucasus, in Transcarpathia and less often in other regions of Ukraine. It appears on the leaves and sometimes in the stalks of corn in the second half of the growing season. Initially, inconspicuous light yellow spots appear on the leaves, on which brownish oblong, randomly scattered pustules up to 1 mm in size, covered with epidermis, are formed. Over time, the epidermis ruptures, the pustules are exposed, and urediniospores scatter from them. Towards the end of the growing season, pustules appear on the corn for the second time, but, unlike the previous ones, they are black, larger and located on the leaves in the form of elongated spots.
Pink mold is a consequence of infection by fungi from the genera Trichothecium Link., Sporotrichum Link, etc. The disease, as a rule, first develops on grains affected by linen, and then spreads to the entire cob. Its intensive development is observed at a temperature of 8-10° and grain humidity on the cob is about 19%. Severe molding of cobs and grain also occurs when storage facilities are poorly ventilated and especially when grains are damaged. Very affected cobs in the piles completely rot. As a result of molding, the energy of germination and germination of seeds sharply decreases, and they become unsuitable for sowing. Grain infected with certain species of Aspergillus cannot be fed to animals or used for human nutrition, as it can cause diseases of the hearing and respiratory tract (inhalational mycoses of the lungs, etc.).
The causative agent of the disease is the lower fungus Rhizopus maydis Bruderl., which forms an abundant nonseptate mycelium with stolons and rhizoids that penetrate plant tissue. On the stolons, sporangiophores with sporangia and sporangiespores are formed one by one or in groups.
Sporangiophores are 120-330 µm long, sporangia are spherical, 110-165 µm in diameter, sporangiospores are yellow, elliptical, 5.5-9.3 x 4.5-7 µm in size. The fungus develops intensively with sufficient humidity and a temperature of 30-35°, so gray rot does not spread during the storage period of the cobs. The pathogen persists in the form of mycelium and sporangiespores on corn residues in the field and other places.
Seeds do not play a significant role in the spread of infection.
P When corn is damaged early, the cobs become underdeveloped, the seeds lose their viability and become very moldy during storage.
Gray-green mold is quite common. Its causative agents are fungi from the genera Penicillium Link., Aspergillus Micheli et Fr., Botrytis Micheli, Mticor Micheli, etc. Most of them begin to develop at a temperature of 8°, and Penicillium species - even at 2-5°, while suppressing other fungi located on the cobs.
Sclerosporosis was discovered in the North Caucasus. It appears on leaves and stems in the form of whitish-yellow or dirty green stripes, on which a barely noticeable whitish coating forms (on leaves mainly on the underside). The affected leaves, and often the entire top of the stem, turn brown and become deformed. Often the stem becomes loosened and the fibers of the conductive bundles become twisted. The panicles thicken and turn into a large number of underdeveloped, densely growing leaves.
The causative agent of the disease is the lower fungus Sclerospora maydis Butler. Its zoosporangiophores are thick and short, with branched apices, at the ends of which colorless spherical or elliptical zoosporangia measuring 28-45 x 16-28 µm are formed. During germination, up to four zoospores can be formed from one zoosporangium.
Plants become infected in the presence of drip moisture during periods of heavy rain and dew. The pathogen persists in the affected plant remains on the soil surface.
Dark mold is caused by fungi of the genera Cladosporium Link, Alternaria Fr., Macrosporium Fr., Coniosporium Link, etc. It is characterized by the formation of black or dark olive-colored mold, mainly in the upper part of the cobs. Primary infection is usually observed at the site of damage to the grain. The development of the disease is promoted by temperatures above 12°.
Charcoal rot occurs in almost all corn growing areas. Causes browning or discoloration of the lower part of the stem and root. Under the epidermis, small black sclerotia in the form of dots are found scattered along the stem. The parenchyma of the core is almost completely destroyed, the stem dries out or becomes soft and easily breaks.
The causative agent of the disease is the imperfect fungus Sclerotium bataticola Taub. In its development cycle, it forms sclerotia measuring 50-152 x 22-32 microns and mycelium, which infects plants. The development of the disease increases with low rainfall and elevated temperatures.
Fusarium is widespread everywhere. It appears in the field on the cobs at the end of the milky or beginning of the waxy ripeness of the grain and develops before harvesting, and sometimes during storage of the crop at elevated temperatures and humidity.
A cobwebby or denser pale pink coating appears in patches on the cobs. The grains in such places become dirty brown and are easily destroyed, especially when threshing the cobs.
The causative agents of the disease are imperfect fungi from the genus Fusarium Link, mainly Fusarium moniliforme Sheldon. In addition to abundant mycelium, it forms microconidia and, in small quantities, macroconidia.
Microconidia are colorless, fusiform-ovate, unicellular or with one septum, 4-30 X 1.5-4 µm in size, formed on the tops of conidiophores in the form of disintegrating chains or false heads. Macroconidia are colorless, spiny or slightly sickle-shaped, gradually tapering towards both ends, usually with 3-5, rarely 6-7 transverse septa, measuring 9.4-6.0 x 4-4.5 µm.
Occasionally, dark blue spherical sclerotia with a diameter of 80-100 microns are formed on the mycelium.
Severely affected corn seeds lose their viability, and seeds with a healthy embryo produce weak sprouts that usually die before reaching the soil surface.
The main source of infection is post-harvest corn residues and especially cob wrappers, the tissues of which contain mycelium, which gives rise to a new generation of conidial sporulation in the spring. Infestation usually begins on ears damaged by insects or affected by corn linen.
The fungus F. moniliforme has no toxic properties, so the cobs affected by it can be fed to animals.
Fusarium rot is known in all corn growing areas. It usually appears on two or three lower nodes and internodes in the form of brown or yellow spots of various shapes, which in wet weather are covered with a red-white or white-pink coating. The stem of affected plants is hollow inside and often becomes macerated. The underground internode and roots become red, and the parenchyma of the core is destroyed.
The causative agents of Fusarium rot are various imperfect fungi from the genus Fusarium Link. They spread by conidia, which are of two types: macroconidia - fusiform or sickle-shaped, with 3-5 septa, and microconidia - one- or two-celled. The latter are often formed during the budding of macroconidia. The disease develops more strongly at elevated temperatures and light precipitation.
About 120 types of pathogens are known. Yield losses amount to 8-12%, sometimes more. Particularly harmful diseases of corn include bubbly and loose smut, fusarium seedling blight, rust, helminthosporiosis, diseases of the cobs and seeds, diplodia, bacterial and viral diseases.
Smut diseases
Blister smut. The causative agent is the basidiomycete fungus Ustilago zeae Unger from the order Ustilaginales. The disease is common in all corn growing areas.
On young growing organs - leaves, stems, internodes, leaf sheaths, cobs and panicles of corn - swellings and nodules of various shapes and sizes appear.
Infection is possible throughout the growing season; the disease usually occurs in a local manner. At the site of infection, a pale, swollen spot forms, which over time turns into a whitish-pink or greenish-yellow swelling, filled with the white pulp of overgrown cells of the host plant, permeated with the mycelium of the fungus. Then the mycelium cells gradually become dense, become covered with a membrane and turn into teliospores. The nodule dries out, darkens, its shell cracks, mature teliospores scatter and secondary infection occurs (at high air humidity and temperature 23...25°).
The source of the primary infection is teliospores, which are stored in smut nodules in the soil and on plant debris, as well as on the surface of healthy seeds. In spring, under favorable conditions, teliospores germinate into four-celled basidia with four basidiospores. Getting with the air flow on the young meristematic tissues of various organs of corn, they copulate and infect the plants.
The harmfulness of smut is determined by the age of the plants at which infection occurred, the number and size of nodules. Death of young plants or infertility of cobs is often observed. The development of the disease intensifies with sharp fluctuations in temperature and humidity, a lack of phosphorus and potassium in the soil, as well as mechanical damage by insects (Swedish fly, etc.).
Protective measures. Crop rotation. Spatial isolation (1000 m) of corn seed plots from the previous year's crops. Selection of predecessors (winter wheat, beets, buckwheat, etc. helps cleanse the soil of smut). Selection, sorting, calibration and disinfection of seeds. Sowing at the optimal time and at the optimal depth. Application of phosphorus-potassium fertilizers. Optimal timing of harvesting and removal of post-harvest residues from the field. Removal of smut nodules before teliospores form. Use of resistant hybrids: Krasnodarsky 436,31OTV, Dnepropetrovsky 438, 320, 56TV, DPG-50, Vostok - 2 ATV, Moldavsky 423JI, Yubileiny 60.
Dusty smut
The causative agent is the basidiomycete fungus Sorosporium reilianum McApl from the order Ustilaginates with a narrow phylogenetic specialization. Distributed in the North Caucasus, Transcaucasia, Moldova, Ukraine and Central Asia.
Corn panicles and cobs, and sometimes sorghum inflorescences, are affected. They completely or partially turn into a black dusty mass (Fig. 21), and in their place an oval-cone-shaped nodule is formed, consisting of the remains of vascular bundles and a huge number of dark spores. At first, the nodule wrappers are dense and green, but by the onset of milky ripeness they turn yellow, dry out and crack.
Spores from it dissipate slowly, as they are retained by the remnants of the fibers of the cob. Head smut is also a cause of plant stunting, excessive leaf growth, fasciation and other deformities.
Teliospores mature at the beginning of the appearance of corn stigmas (threads) and, sprayed, fall on the soil, and partially on the grains, especially during the harvesting period. Teliospores remain viable for 3-4 years in the soil, on the surface of spores, cobs and on plant debris.
Infection of plants usually occurs during the period from the beginning of seed germination to the emergence of seedlings, sometimes in the phase of 2-3 leaves. The mycelium quickly moves along the stem and reaches the growth point. The disease develops in a diffuse manner and appears at the time of flowering.
The harmfulness of loose smut lies in the death of individual seedlings, underdevelopment of plants and cobs. With monoculture, corn yield losses increase greatly.
Protective measures. Spatial isolation of fields. Seed disinfection. Optimal sowing dates. Removal and destruction of diseased plants in seed plots before harvesting. Timely cleaning and removal of post-harvest residues. Stubble peeling and deep fall plowing. Use of resistant varieties and hybrids.
Rust
It is found in Transcaucasia, on the Black Sea coast of the Caucasus, in Transcarpathia and less often in other regions of Ukraine. The causative agent is the dioecious basidiomycete Puccinia sorghi Schw., which forms uredinia with uredinospores and telia with teliospores on corn.
In the second half of the growing season, light yellow spots appear on the leaves (sometimes on the stems) of corn, on which brownish oblong randomly scattered pustules up to 1 mm in size, covered with epidermis, then form. After the epidermis ruptures, urediniospores scatter from the pustules. By the end of the growing season, the pustules become almost black and are located on the leaves in the form of elongated spots.
During the harvesting period, urediniospores fall on the cobs and, together with the seeds, on new corn crops.
The spermogonial and aecidial stages of the fungus occasionally form on sorrel weeds (Oxalis L. spp.), a common corn weed in the southern regions. Primary infection of corn most often occurs from urediniospores, which in the south overwinter well on the remains of infected plants. The optimal temperature for germination of urediniospores is 17...18° at absolute air humidity. The incubation period is 5-8 days. Over the summer, 2-3 generations of urediniospores are formed. The role of teliospores in maintaining infection is small. They germinate in the spring, forming basidia with basidiospores.
The harmfulness of rust manifests itself in the premature drying of leaves, as a result of which the ears are underdeveloped and puny grains are formed in them.
Protective measures. Crop rotation. Destruction of post-harvest residues. Deep fall plowing. Destruction of the intermediate host. The use of resistant varieties (varieties of dent corn are characterized by increased resistance, sugar - reduced).
Brown spot, or helminthosporium
Found in Transcarpathia, Georgia and Primorsky Krai; in some years - in the North Caucasus, southern Ukraine, Armenia and the Baltic states.
The causative agent is the imperfect fungus Helminthosporium turcicum Pass from the order Hyphomycetales. The disease usually begins with the lower leaves. Drying brown or brown oblong spots appear on them, stretched along the plate. Over time, the spots increase, often merge and cover the entire blade, the leaves dry out and die. Greenish or dark spots with a border of various shapes form on underground and above-ground internodes. On cobs, the disease is found at the base and in the depressions between the grains in the form of a thick dark brown felt coating consisting of multicellular mycelium, conidiophores and conidia.
The pathogen persists in the form of mycelium on plant debris both on the soil surface and at a depth of up to 10 cm, as well as in the form of conidia on the surface of seeds. In the spring, new conidial sporulation forms on the mycelium, spreading to the corn crops. The disease leads to a significant shortage of grain and green mass.
Protective measures. Since there are no hybrids or varieties of corn with high resistance to the disease, seed disinfection is mandatory. Crop rotation. Deep fall plowing and removal of crop residues from the field. Application of mineral fertilizers (especially phosphorus-potassium). Optimal sowing dates (later ones suffer more from helminthosporosis).
Diplodia
Distributed in Georgia. The causative agent is the imperfect fungus Diplodia zeae Lev from the order Sphaeropsidales. It affects ears, stems, leaf sheaths and leaves.
The stems, often the lower internodes, turn brown, then soften and break. A white mycelium forms under the leaf sheath, and then point-shaped, initially white, and later black pycnidia protruding from under the epidermis. Brown spots also appear on the leaves, sometimes with pycnidia. The cobs are covered with a continuous cotton-like coating, spreading to the adjacent wrappers. On the grains, especially near the embryo, inside the stem and on the involucres adjacent to the cob, round or slightly flattened blackish-gray pycnidia with a large number of pycnospores are formed.
The disease develops at high relative air humidity, especially at elevated temperatures (20...30°). Sources of infection are seeds and plant debris, on which the pathogen persists for 3-4 years.
Protective measures. Selection of healthy cobs for seed purposes. Early disinfection of seeds and optimal storage conditions. Sowing at the optimal time. Application of phosphorus or complete mineral fertilizer. Compliance with crop rotation. Spatial isolation of fields. Removal of crop residues followed by deep fall plowing. Use of resistant varieties. Restriction of the import of seeds from areas where diplodia is widespread.
Diseases of cobs and seeds
Corn cobs and seeds during ripening and storage are affected by many fungal and bacterial diseases, among which the most common are fusarium, red and gray rot, mold, bacteriosis and white. In addition, smut diseases, helminthosporiasis, white rot and nigrospora are observed.
Fusarium. The causative agent is an imperfect fungus from the genus Fusarium Link., predominantly Fusarium moniliforme Sheldon. On the cobs at the end of milky or at the beginning of waxy ripeness of the grain, a cobweb or more dense pale pink coating appears in patches. The grains become dirty brown and are easily destroyed.
The disease develops until harvesting, and sometimes during storage of the crop (at elevated temperatures and humidity). Along with the mycelium, micro- and macroconidin are formed, and occasionally dark blue spherical (80-100 µm in diameter) sclerotia are formed.
Sources of infection are post-harvest residues, especially cob wrappers, in the tissues of which there is a mycelium that produces new generations of conidial sporulation in the spring.
Severely affected corn seeds lose their viability, and seeds with a healthy embryo produce weak sprouts that usually die before reaching the soil surface. First of all, cobs damaged by insects and affected by linen become infected.
Red rot. The causative agent is an imperfect fungus Fusarium graminearum Schwabe from the order Hyphomycetales. It is more often found in fairly humid areas of the North Caucasus and the Far East.
It appears during the period of milky-waxy ripeness of the grain in the form of a bright pink coating on the top of the cob. The wrappers fit tightly to the cob and become reddish-brown in color. The grains are also painted the same color. They become fragile and are filled with mycelium inside.
The fungus develops intensively at excessive or moderate humidity and temperatures of 30...35°. The pathogen persists as a mycelium on plant debris. The infection is practically not transmitted by seeds.
With early damage, the cobs become underdeveloped, the seeds lose their viability and become very moldy during storage. Crop losses from red rot can reach 3-4%.
Gray rot. Distributed in the southern regions of Ukraine, Rostov and other regions of Russia.
The causative agent is a lower fungus from the order Mucorales Rhizopus may-dis Bruderl, which forms an abundant mycelium with rhizoids that penetrate the plant tissue.
It appears at the beginning of the milky-waxy ripeness of the grain in the form of a thick gray coating between the rows of grains, rot spreads from top to bottom. The grains turn brown, die and crumble easily.
The pathogen persists as a mycelium of sporangiospores on corn cobs. The fungus develops with sufficient humidity and temperature 30...35°. Seeds do not play a significant role in the spread of infection. When corn is damaged early, the cobs become underdeveloped, the seeds lose their viability and become very moldy during storage.
Mold of cobs and grain is common in all areas of corn cultivation, especially in conditions of high humidity during harvesting and storage.
Gray-green mold. Pathogens are fungi from the genera Penicillium Link., Aspergillus Micheli et Fr., Botrytis Micheli, Mucor Micheli, etc. The development of most of them begins at a temperature of 8°, and Penicillium species - even at 2...5°, other fungi , located on the cobs, are suppressed.
Dark mold. Pathogens are fungi of the genera Cladosporium Link., Altemaria Fr., Macrosporium Fr. etc. The upper part of the cobs is mainly affected. The cause of primary infection is often contaminated grain. The development of the pathogen begins at temperatures above 12°.
Pink mold. Pathogens are fungi from the genera Trichothecium Link., Sporotrichum Link, etc. The disease develops on grains affected by linen, and then spreads to the entire ear. Grain infected with certain species of Aspergillus cannot be fed to animals or used for human nutrition, as it can cause diseases of the hearing and respiratory tract (inhalational mycoses of the lungs, etc.).
Cob bacteriosis is common in all corn-growing areas of the country. During the period of milky ripeness, depressed spots of pale gray color appear in the upper part of the grains. The carrier of the pathogen is the bread bug, in whose body Bacillus mesentericus var. vulgatus Flugge. The harmfulness of bacteriosis lies in the reduction in the keeping quality of the cobs, their rapid molding and the deterioration of the seed qualities of the grains.
Protective measures. Removal from the field and burning of all post-harvest residues, followed by deep fall plowing. Destruction of insect vectors.
White cobs practically do not reduce the corn yield, but significantly deteriorate its quality. Fusarium and mold fungi actively develop on the affected cobs.
Viral diseases
The most common is corn mosaic virus (Maize mosaic virus). The virus is transmitted by leafhoppers. Mosaic streaks and spots appear on leaf sheaths, cob wrappers and stems of diseased plants. The productivity of affected plants is reduced by 5-10%.
Non-communicable diseases
With a lack of nitrogen in the soil, corn leaves turn yellow and die, starting from the lower ones. Lack of phosphorus leads to slower root growth. The leaves become dull in color with a reddish or purple tint. Potassium deficiency causes yellowing of the tops and edges of first the lower and then the upper leaves. Often the leaves die off completely. With a lack of manganese, magnesium, boron and other trace elements, yellow-green spots and chlorine swelling form on the leaves.
Corn diseases can be caused by viruses, bacteria and very often fungi. The quality and quantity of the harvest sharply decreases. If measures to combat them are not taken in time, diseases can lead to complete loss of the crop. By knowing the first signs of a problem, you can stop the further spread of the infection.
Corn is a cereal crop. If corn crops are susceptible to diseases and pests, then it will not be possible to get a good harvest. To prevent the occurrence of infection, as well as its spread, you need to be able to recognize the first signs of a problem and take timely measures.
Infection with diseases occurs due to poor-quality planting material, improper crop care, and untimely pest control. Therefore, it is so important to establish a watering schedule, apply fertilizers on time in order to form good immunity and follow other agricultural practices.
Dusty smut
The fungal disease loose smut affects the panicle and ear of corn. This is a common disease in humid areas of the southern regions (Kuban, Transcaucasia). Sick plants look weak, grow poorly, bush heavily, and the ears form weakly. Gradually, the affected ears turn black, become covered with spores and turn into a dusty mass.
The cause of the disease is contaminated soil, poorly treated seeds, and high air temperatures. The main measure to combat loose smut and blister mold is the treatment of seed material before sowing and compliance with annual crop rotation. You should choose varieties and hybrids of corn that are resistant to these fungal diseases.
If diseased plants are found in the garden bed, they must be destroyed (it is better to burn them or bury them to a depth of about 50 cm). Every three years it is recommended to plant corn on a new plot of land.
Blister smut
The causative agent of corn smut is a fungus that affects the entire above-ground part of the plant. Small pink or greenish swellings appear in the affected areas. Over time, the swelling grows and becomes black in color. Soon the bubble shell ruptures, and the spores, with the help of wind and insects, fall on other, healthy plants.
The source of infection is infected plants, untreated, contaminated seeds. Bladder smut is especially harmful when it appears on the internodes of the stem and cob. In this case, the grain yield is reduced to 50%. The disease is provoked by drought and late sowing of plant grains.
The main preventive measures are the selection of varieties and hybrids of corn that are resistant to smut, treatment of planting material, removal of plant residues from the site after harvest, and compliance with crop rotation. Seeds are collected only from healthy plants.
Effective drugs for bubbly smut, as well as for root and stem rot, are considered to be: Protravitel Alpha, Delit Pro, Vincet, Lanta, Pioneer, Maxim XL.
Fusarium
Fusarium corn blight can appear at any stage of plant development. The causative agents of the disease are fungal spores found in swellings. The disease leads to rotting of seeds, roots and stems, as well as ears. Accordingly, the symptoms will differ.
Rotting of seeds and seedlings occurs as a result of sowing infected planting material. Most seeds rot in the soil without forming the first shoots. A light or pinkish coating forms on their surface. Young plants grown from infected seeds on the surface of the ground look weak, are sharply retarded in growth and form cobs poorly.
During the milky-waxy ripeness phase, stem and root rot often appears. The leaves of the plant wither, turn yellow, and dry out. The roots turn black, dry out, and the affected corn is easy to pull out of the ground. Gradually the cobs themselves dry out and wither.
Ear rot can occur even during storage of the harvested crop. First, a white-pink coating appears on the grains, and gradually the entire cob is affected. The color of the plaque darkens and becomes brownish-gray.
The source of infection is contaminated seeds or uncollected plant debris on the land. The disease can be provoked by wet, cold weather, high air temperatures during the period of ripening of cobs, damage to cobs and grains by pests.
Before planting, be sure to treat the seeds, select fusarium-resistant varieties and hybrids of corn, and promptly detect and remove diseased plants. Autumn plowing of the land and removal of plant residues, timely control of insect pests are shown.
Stem rot
The fungal disease stem rot appears at the end of the growing season at the stage of milk maturity of corn. The description of this maize disease is as follows: the leaves become gray-green in color and become covered with a matte coating, dry out, and wither. A pinkish coating can be observed on the stem; over time, it softens and breaks.
The source of infection is the persistence of spores in plant debris after harvest. The fungus actively reproduces in hot, dry weather. The provoking factor is improper watering and too thick sowing of corn.
To increase the resistance of plants to rot, you need to observe the optimal sowing time, planting density and seeding depth; after harvesting, you need to dig up the area and remove all plant debris; you must treat the planting material with fungicides.
Southern helminthosporiosis
Most often, the leaves of the plant suffer from southern helminthosporiosis of corn, less often the roots and the cob. The first signs of the disease are the appearance of brown oblong spots on the leaves. Gradually the affected area dries out. The spots grow and occupy the entire leaf area.
Corn spot or helminthosporiosis appears in mid-summer. The provoking factor is high humidity and low air temperature. The source of infection spread is untreated seeds and plant residues.
Before planting, the seeds must be sorted and treated. If infected seeds are planted, the seedlings produced are weak and often unable to reach the soil surface. To increase immunity, fertilizers are applied to the soil several times a season. It is not advisable to plant corn for three years in a row in the same area.
Corn pests, their signs and control measures
Insect pests are considered one of the reasons for the spread of diseases among grain crops. To combat them, you can use both folk remedies and ready-made drugs.
Stem borer
Corn pests eat the above- and underground parts of the plant, causing it to weaken and become susceptible to disease. In addition, the pests themselves can transfer pathogenic bacteria from a diseased plant to a healthy plant.
It is not the adults that cause the greatest harm to the plant, but the moth caterpillars. Gray-yellow caterpillars (25 mm in length) are especially active in July-August, when the weather is dry and warm. Corn stem borer caterpillars live on the surface of plants, burrowing into the petioles of stems, leaves and panicle flowers.
Plant nutrition is disrupted, and sometimes stems can break. The plant begins to bloom later, the size of the leaves decreases, and pollination deteriorates.
To prevent the spread of the meadow borer on corn, it is necessary to fight weeds, mow them around the plantings, and not leave the tops after harvesting.
Root aphid
Root aphids most often attack corn in hot, dry weather. The plant slows down in growth, the leaves turn yellow and dry out, and is easily affected by fungal diseases. If the area where the infection spreads is small, then you can pick off the diseased plants.
Insecticides and fungicides (Confidor, Actellik, Fitoverm, Fas) are used to protect plants from pests. Since insects can overwinter on the remains of stems, after harvesting the area must be cleared of all vegetation. It is best to choose early ripening varieties of corn.
Swedish fly
The Swedish fly most often infects corn during seedling germination. The larvae damage young seedlings, and they begin to lag behind in growth and development. The leaves of the affected corn become dark green and the stem thickens. Corn pests reduce not only the quantity of the crop, but also its quality.
During the period of mass flies and egg laying, it is recommended to treat the plants with preparations such as Karate, Decis, Cyperon. As a preventive measure, it is useful to fertilize with nitrogen fertilizers, observe optimal sowing dates and select resistant varieties of corn.
Preventive measures
Prevention should begin from the moment the seeds are selected and end with clearing the field of plant residues. Preventive measures:
- It is better to choose early ripening varieties of corn.
- It is advisable to treat the seeds.
- When planting, it is recommended to add potassium-phosphorus fertilizers to the soil.
- It is important to know the first signs of the appearance of diseases and pests.
- Remove damaged plants from the site in a timely manner.
- Dig the field deeply in the fall.
Another common disease in corn is bacterial wilt, or wilt. The bacterium affects all organs of the plant. Light green and yellow stripes appear on the leaves.
