Corn smut symptoms and prevention methods

What should we do if smut appears in the process of planting corn? Today I will tell you about the prevention and control methods:

Symptoms of corn smut

Commonly known as gray bag and black mold. It harms the young and tender tissues of the aboveground part of the plant, such as stems, leaves, female ears, male ears, axillary buds, etc. The affected tissues are stimulated by pathogens to swell into tumors. When the diseased tumor is immature, it is covered with white or light red shiny tender tissue, which later turns gray or gray-black, and finally the outer membrane ruptures, releasing black powder, which is the thick-walled spores of the pathogen. The shape and size of the diseased tumor vary depending on the site of the disease. The tumors on the segments and leaf sheaths are the size of beans, and no or very little black powder is produced. The tumors on the stem nodes and ear are as big as fists. There are often multiple tumors on the same plant, or several tumors gather together at the same position. The stems of the plants are often twisted, and the diseased plants are shorter. The disease is early, the ear is small, and even cannot produce ears. The disease can invade any part of the plant, forming tumors, and scattering black powder after rupture, which is different from the hairy smut. Hairy smut generally only attacks the ear and male ear, and there are messy black filaments.

Morphological characteristics of corn smut

Corn smut, also known as corn gall disease, can occur in all growth stages, especially in the heading stage. Tumors of varying sizes appear on the affected parts. In the early stage, the tumors are covered with a white film, which then turn gray. The tumors are rich in water and emit black powder after drying and cracking, which is the spores of the pathogen. Tumors the size of beans are easily produced on the leaves. Galls are produced on the male spikes, and large tumors are formed on other parts. Pathogen: It is called Ustilago maydis, which belongs to the Basidiomycetes.

The thick-walled spores are spherical or ovoid, yellow-brown, with obvious fine thorns on the surface, and are 8 to 12um in size. When the thick-walled spores germinate, they produce septate promycelium, and 4 colorless fusiform basidiospores grow on the sides. The basidiospores germinate to produce infection threads, and the secondary microspores produced by budding can also germinate to produce infection threads. Corn smut reproduces by heterothallic combination and forms colonies by continuous budding on artificial culture media. The fungus has multiple physiological subspecies.

Mode of transmission

The pathogen overwinters in soil, manure or diseased plants, becoming the source of infection in the early next year. Seeds carry the bacteria for long-distance transmission. When the temperature rises in spring, the thick-walled spores that overwinter on diseased remains germinate to produce basidiospores, which are spread by wind, rain, insects, etc., causing tumors to form in the seedling and adult stages. After the tumor ruptures, the thick-walled spores can also re-infect. The disease occurs most quickly during the heading and flowering stage of corn, and does not stop until the corn matures.

Conditions of disease

The optimum temperature for thick-walled spore germination is 26-30℃, with a maximum of 38℃ and a minimum of 5℃. The optimum temperature for basidiospore germination is 20-25℃, with a maximum of 40℃, and the optimum temperature for invasion is 26.7-35℃. After germination, these two types of spores can directly invade the plant without passing through the stomata. High temperature and high humidity are conducive to spore germination. The host tissue is tender, and mechanical wounds are easy for pathogens to invade. Corn is affected by drought and has weak disease resistance. It will be seriously ill when there is light rain or much fog and dew. It is easy to get sick when it is dry in the early stage and rainy in the later stage or alternating dry and wet. The disease is serious in continuous cropping or high-fertilizer and densely planted land.

Corn smut prevention and control methods

(1) Plant disease-resistant varieties. Generally, drought-resistant varieties are more disease-resistant. Dent corn is more disease-resistant than sweet corn. Early-maturing varieties are less susceptible to disease than late-maturing varieties.

(2) Strengthen agricultural control. Control corn borers and other pests in early spring to prevent wounds. Cut off diseased tumors before they rupture and bury them deeply. Remove diseased remains in the field after harvest in autumn and turn the soil deeply. Implement three-year crop rotation. Apply fully decomposed organic fertilizer. Pay attention to drought prevention and prevent uneven drought and flooding. Irrigate in time before emasculation and avoid drought. Cut off diseased tumors in seed fields before emasculation and bury them deeply. Do not discard them in the field at will to reduce the spread of pathogens in the field.