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The most important viral disease of corn. At the early stage, yellow stripe mosaic symptoms are produced along leaf veins. The entire plant greatly shrinks if occurring severely. The causal virus is transmitted by the aphid which are occurring in May around. The causal virus, ScMV, is divided into the more than 10 strains based on the reaction of differential varieties of sugarcane. The ScMV-B strain is occurring in Japan. Moreover, the same virus is parasitizing fingergrass and foxtail millet, etc. and they are considered to be primary disease spreader. |
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One of important viral diseases and the resistance to the disease should be checked in pre-cultivating tests in Japan. Leaves get rolled up and the internode above ear is especially blocked. As a result, the entire plant shrinks when it occurs severely, and the height of plants become 1/3 or less compared with a healthy plant. It is characteristic that the streak of the upheaving row white - reddish brown appears in the other side of the leaf and the surface of the bract. The causal virus is transmitted by planthoppers, and infects various gramineous crops including rice. |
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Bacterial disease. Lesions are at first ash white, small oval lesion in a young leaf. Later it gradually extends long along leaf veins, and it becomes a stripe which reaches 30cm in length and 5-6mm in width. The lesion part becomes thin like a paper and to split easily. Occasionally, it occurs in an upper stalk of the ear and then the ear becomes sterile and the whole plant withers. A lot of bacteria are detected from the infected leaf, and they disperse and transmit by wind and rain, etc. |
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Bacterial disease whose damage is big when occurring severely. The occurrence of the disease became a problem in Yamanashi and Shizuoka Prefecture before. It gets sick from the rainy season to the early summer most violently. At first, the water-soaked lesions are produced in a young leaf. And then, the inside tissues of the stalk gradually soften and the pith of the ear and the culm rots finally. The bacteria invade from the scar of insect's bite, etc. The stalk rots from the infected part in brown, and then the plant lodges. The bacterial ooze from the diseased plant is carried and transmitted by wind, rain and insects. Two kinds of bacteria are known as pathogens in Japan.
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Spot-causing bacterial disease occurring increasingly especially in warm regions such as Kyushu District. After the rainy season, lesions that are ash white to yellow brown, stripe, and 2-10cm in length and 3-5mm in the width are produced. It often becomes little short spots in rows rather than long stripes such as in sorghum. The symptom often begins to appear from lower leaves and rarely appears on upper leaves. Therefore, the damage is limited and it has not become a severe problem. The occurrence increases under the wet condition when the rainy season is prolonged, etc. |
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Spot-causing fungal disease occurring from the end of the rainy season. Lesions are yellowish brown to ash white with blackish brown border, oval. Later they fuse mutually and become irregular shape. It is characteristic that the center of the lesion becomes black moldy because of production of setae, fungi tissues. Orange slimy mass of spores are formed among the setae, and these disperse and spread by wind and rain. |
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Spot-causing fungal disease mainly occurring in young plants. The disease produces spindle-shape, ash white lesions on the leaf. It mainly occurs in the green house, but rarely occurs in the field. The pathogen is reported to be same with that of fingergrass. But those of rice and African millet are also reported to cause blast in corn, so the life cycle of the fungus has not well known. |
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Fungal disease that makes tassels and ears moldy. The mold of ash green is produced in the grain and ear. The pathogen often stays in the seed coat, but sometimes invades the embryo in the grain. It often infects ears in the field and extends while storing them. The disease is transmitted by seeds. In that case, the seeds are covered by blue mold in the soil when sowed and this induces seedling blight. The infection ability of the pathogen is weak and it often infects from the scar of insect's bite, etc.
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Spot-causing disease which often occurs in bracts of ear. Lesions are at first small points of fading green color and later it becomes brown or brownish purple, round or oval, 2-5 mm in diameter. When the lesions fuse, it becomes an irregular shape. And then, the epidermis is broken and looks like powdery exposing the resting spore in inside. The infected tissues drops to ground and overwinters. The spores germinate in next year, and release the zoospore for spreading. |
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The only downy mildew disease occurs on corn in Japan. The disease begins to occur in the rainy season. The lesion is yellow to yellowish brown, delimited by the leaf vein, rectangular to stripe, 0.5-2 cm in length and 3-7 mm in width. The lesion elongates long, and becomes purple red, and the entire leaf withers. The damage is limited to lower leaves and not so severe now in Japan. About 30 in temperature of the soil is suitable for the occurrence. The pathogen is considered to infect fingergrass. |
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Unregistered fungal disease in Japan. The disease are likely to occur in young plants or adult plant at yellow ripe stage. Black brown lesions are at first formed in roots. Then, the pathogen extends into the stalk of the ground side part and the causes lodging. A black, minute sclerotia is formed in the stalk. It looks sooty because black microsclerotia are produced in the stalk. M. phaseolina isolated from other crops such as soybean was reported
not to be pathogenic to corn.
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