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Soil-borne disease that causes damping-off of seedlings in wet conditions at germination. The seeds infected by the disease cannot sometimes germinate, but in many cases, small seedlings at the 3-4 leaf stage get infected and wilt. When the disease is caused by Fusarium, the seeds are covered with pinkish hypahe, whereby the grayish green hypahe covers seeds by Penicillium. Achlya (Saprolegniales) was also reported to cause the disease, causing severely restrained growth and death of seedlings. The disease often occurs under high temperatures, whereby Pythium seedling blight under relatively low temperatures. |
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An important fungal disease which leads to withering of the entire plant body if occurring severely. The disease firstly occurs in the ground side of stem around the rainy season and progresses up through sheaths. The lesion becomes cloud-shaped, ash white with brown border. Brown sclerotia with a smooth surface are produced on the lesion at the latter stage of the occurrence. They drop to ground, and become the primary inocula of next year. It occurs severely under high temperature (especially 30C or more) and high humidity condition and the lesion progresses by 1cm or more a day. Most of pathogen are R. solani AG-1 IA in the corn and this is common in summer blight of pastures and sheath blight of rice and sorghum, etc. |
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Fungal disease that causes malformation of plant body. White-surfaced galls (hypretrophy tissue) filled with black powder (smut spore) are formed in the leaves, nodes, tassels and ears from the end of the rainy season. The smut spores are clamidospores, drop to ground, and become the primary ionocula of next year. They are considered to live more than five years in the soil. The fungus has many races and biotypes, but those occurring in Japan have not yet identified. |
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The most important fungal disease. The disease begins to occur at the end of the rainy season and the lesions that are orange to yellow brown, oval, 0.5-2cm in length, and 2-5mm in the width are produced in leaves and sheaths. The entire plant is often killed when the disease occurs severely. The occurrence of the disease increases from August to September at the later period of growth. The conidia of the pathogen disperse by wind and rain. These races are known responding to the types of male sterile cytoplasm of corn and race O is mainly occurring in Japan. |
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Rust disease that damages corn severely especially in Kyusyu District, the southern region. The disease begins to occur after milk ripe stage in the upper leaf. It occurs severely in the condition of high temperature and humidity. In that case, the entire leaf gets dry and turns yellow, the whole field of diseased plants sometimes looks yellow. Uredinia is yellow to orange, round to oval, 1-3mm in length, and 0.5-2mm in width are formed abundantly on the diseased tissue and many urediniospores are produced in it. The stroma turn brown at the end of summer and change to telia.
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Fungal disease which occurs mainly on sweet corn in mid-summer. It often produces lesions from the leaf rim and the lesion becomes oval, black brown. Later it becomes zonate spot when extending to some degree. Slimy masses of conidia are produced on the surface of the lesion, and they disperse by wind and rain, etc., especially under high temperature and humidity conditions. When the lesion becomes old, small sclerotia are formed in the infected tissues, and then the sclerotia overwinter and become the primary inoculum source of the disease in the next year. The species of the pathogen is same with those on orchardgrass and timothy, but differed in pathogenicity. |
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The insect damage occurred in 1988 in Kumamoto Pref., Kyushu first in Japan. The symptom is characteristic that the upheaved streaks appear on the surface of the leaf of young plants. The entire plant distictly shrinks when it occurs severely. Although the symptom was at first thought to be caused by virus, Maize wallaby ear virus (MWEV), now is considered to be the insect damage or a toxin from the insect, corn leaf hopper (Cicadulina bipunctata). The distribution of the insect has enlarged in the north area of Japan accoring to the global warming, and the damage may become more severe in the near future. |
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Disorders along the leaf edge are often observed in the vegetative growth stage. In USA and other countries, it is not a severe problem, but the symptoms are often observed in Japan, since potassium surplus occurs commonly in results of the excess application of animal feces to the fields in Japan. Potassium surplus is thought to cause the inhibition of calcium absorption by corn plants. Although the degrees of the symptom are different among corn cultivars, the degrees from the vegetative growth stage to the silking stage should be the indicator for the balance of the soil minerals including potassium and calcium. Farmers can modify the potassium (manure) application by the index. The symptom does not affect the yield of corn. |
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