There are more than 30 diseases occurring on corn, and there are more than 10 major diseases of corn in Yunnan Province. The annual output loss of corn caused by various diseases accounts for about 10% of the total and seriously reduces the quality of corn products.
The following are the most common conditions of leaf disease formation and its control measures.
First, the most common diseases in corn leaf diseases are:
1, corn leaf spot: the main damage to the leaves, but also invade leaf sheath and temporal lobe. At the beginning of the disease, water-stained gray-gray or gray-green spots appear, and then spread along the leaf veins to both ends to form prismatic or long spindle-shaped large spots, generally more than 50 mm in length. The central spot is light brown with dark brown edges, and several lesions merge into large pieces after fusion. When the weather is wet, dark gray molds (conidia) can develop on the lesions.
2. Maize canker disease: It can occur from the seedling stage to the adult stage, and the disease is gradually increased after tasselling. The bacteria mainly harm the leaves, and in severe cases it can also damage leaf sheaths, temporal lobes, ears and grains. The lesions were water-stained at the beginning, followed by a gradual yellow-brown or red-brown near-circular or oblong lesion with darker edges. During the wet or rainy season, there will be a gray mold layer on the lesions.
3. Gray spot disease of corn: Gray spot disease mainly damages the leaves and also invades leaf sheaths and loquat leaves. The initial stage of disease is water-stained, light-brown spots. After that, it gradually expands gray-brown, gray to yellow-brown rectangular strips, and veins. Parallel extension, in the late stage can produce black and gray mold layer on both sides of the blade, lesions can be extended to the entire plant leaves, eventually leading to the death of the diseased plants, the premature decline of the ear, the grain loosening and dryness, a thousand grain weight decreased.
4. Curvularia leaf spot disease: also known as maculopathy, eye spot disease, mainly damage corn leaves. At the beginning of the lesion, it was a small green spot. Mature lesions were round or oval in shape. The center had a yellow-white or grey-white necrosis zone with brown edges and a halo around the periphery, resembling an eye. Occasionally, multiple spots can merge longitudinally along the veins to form large spots and even whole leaves die. In moist conditions, black and white moulds can be produced on both sides of the lesion.
Second, the occurrence of corn leaf spot conditions:
1. Variety disease resistance: There is a significant difference in resistance to germs among maize varieties.
Planting susceptible varieties is the main cause of disease epidemics.
2. Pathogenicity of pathogens: The presence of a large number of pathogens with strong pathogenicity is an important factor in the occurrence of diseases, especially the new physiological races with strong virulence and resilience that are caused by pathogens through mutation. Type of disease. It is also related to the effective transmission of pathogens.
3. Meteorological factors: In the case of susceptible strains with a certain amount of bacteria and a certain area, the incidence of leaf spot disease is mainly determined by temperature and rain.
Large spot disease: The optimal temperature for onset is 20-25 °C, and more than 28 °C has an inhibitory effect on the disease;
Small spot: moderate temperature of 25-30°C
Curvularia leaf spot: The optimal temperature is 28-30°C
Gray spot disease: Summer rainy weather
Humidity conditions suitable for the disease are relative humidity above 90%, which is beneficial to the formation, germination and invasion of spores. Rain and high humidity and insufficient sunshine are all conducive to the occurrence and epidemic of leaf spot disease.
4. Cultivation conditions: Continuous crops are heavy and crop rotation is light;
It is very ill and monotonous.
Cultivated dense land;
Corn fields away from the village or corn stalks are lightly diseased;
The low-lying plots are seriously ill.
Third, corn leaf spot control methods
According to the formation conditions, prevention and control strategies: to promote and utilize disease-resistant varieties, to strengthen the cultivation and management, and timely supplemented with pharmaceutical control.
1. Planting resistant varieties
At present, Yunrui 505, Yunrui 8, Yunrui 88, Yunrui 220, Deyu 5, Deyu 6, Yunde 3, Yunrui 999, and Grain 1790 are all resistant to disease.
2. Agricultural control
Objective: To reduce the source of bacteria; to increase plant resistance; to create an environment conducive to the growth of the host and not conducive to disease.
(1) Increased manure application can improve the host's resistance to disease, such as applying base fertilizer, timely fertilizer application, and reasonable compatibility of nitrogen, phosphorus, and potassium.
(2) Do a good job of field sanitation, remove the diseased plants (leaves) in time, such as deep-buried diseased bodies, and promptly remove the bottom leaves.
(3) Proper close planting and reasonable irrigation
3. Chemical control
Although the use of chemical agents to control corn leaf spot disease is difficult to promote in production, it is still a remedy in some cases and at the early stage of disease.
At present, effective agents for controlling leaf spot disease include: 10% Shigao, 70% mancozeb, 70% kill, 50% acetaminophen, triadimefon, and Nova.
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