1. Occurrence Situation Occurrence of corn smut occurred in the northeast spring maize area in 2002, covering an area of ​​1.067 million hectares. Among them, the incidence of diseases in Heilongjiang Province is 440,000 hectares, accounting for 20% of the province's corn area. The main varieties are Longdan 19 and Baidan 31, and the incidence rate is 14% to 70%. Jilin Province has an area of ​​600,000 hectares, accounting for 30% of the province's corn area. The incidence of common varieties is about 7%, and the incidence of susceptible varieties is 10% to 40%; for example, K508, Corridor 6th, Simil 21, Simu 25, Shandan 911, Longdan 13, Dan 2100, Xintie Single 10, Longfeng 1, Longfeng 2, Iron 12 and Nongda 3138. The incidence of individual high-inductance varieties is more than 50%, such as Jidan 209, Dandan 44, Denghai 1, Dongdan 60, Dan 638, Dan 639 and so on. The incidence of diseases in Liaoning Province was 33,000 hm2, accounting for 2.3% of the province's corn area. The main varieties are Shendan 16 and Dan 638. The incidence rate is between 9% and 30%. The incidence of corn smut is equal to the loss rate. It is estimated that this year's production loss due to smut of corn is between 10% and 15%. 2 Occurrence of corn smut The disease is dominated by soil-borne disease and infestation at the seedling stage. The pathogenic bacteria was Sporisorium reilianum KuHnLandonetFull]. With winter spores scattered in the soil, mixed with manure or attached to the seed surface for winter, the winter spores can survive in the soil for 3 years. Soil carriers and manure mixed with diseased tissue are the major sources of infestation. Although the bacteria on the surface of the seed can be transmitted, the infection rate is extremely low. It is the source of infection transmitted from a distance. The incidence of corn smut severity depends on the disease resistance of the varieties and the number of bacterial sources in the soil and the impact of environmental factors on sowing and emergence. This year the main cause of the occurrence of smut in corn is the continuous cropping of corn for many years, blindly introducing some late-maturing High-intensity varieties have increased the accumulation of pathogenic bacteria in the soil, unusual changes in climatic conditions, and farmers' lack of scientific knowledge about the use of seed coating agents. 2.1 The increase in the amount of accumulated bacteria in the soil indicates that the number of bacteria in the soil will increase by 5 to 10 times per year when high-susceptibility varieties are continuously planted. Most of the corn in the northeast spring corn zone is continuously cropped for 3 to 5 years. A sufficient amount of bacteria causing the occurrence of head smut was accumulated in the soil. 2.2 Lack of Disease-Resistant Varieties In the provinces of Heilongjiang and Jilin, the incidence of disease above 10% is mostly cultivated in Huanghuaihai region, such as Liaoning and Shandong provinces. In the plains of this area, the incidence of corn smut is mild, and the selected varieties lack resistance to smut. In the experimental field of the early-season spring corn group in the northeast of the Xinxing Township, Xincheng Township, Shuangcheng City, Heilongjiang Province, there were 11 cases (13.3%) of the 15 varieties participating in the trial, accounting for 73.3%. In the Jilin Provincial Academy of Agricultural Sciences Plant Protection Division, the Northeastern Early-season Spring Corn Group Disease Resistance and Infestation Nursery in the National Maize Regional Examination, the incidence of artificial vaccinations under the conditions of more than 10% accounted for 57.7% of the total number of tested varieties. It shows that most varieties currently selected are susceptible varieties. At the same time, in the validation of the varieties, the evaluation of the resistance of hybrids lacks uniform standards. Taking the three eastern provinces as an example, the artificial resistance in the inoculation of head smut in Heilongjiang Province was 30%, and the field was naturally identified as 3%. In Jilin Province, artificial inoculation of head smut was identified as 20%, and the field was naturally identified. It is 10%; the artificially inoculated head smut in Liaoning Province identified 25% of the defensive limit, and no natural identification in the field was used as a reference. The lack of strict approval of the varieties led to the circulation of susceptible varieties in the market, resulting in the occurrence of head smut. 2.3 Unusual change of weather conditions High temperatures in early spring this year, soil moisture is good. The peasants robbed and sow planting, usually around April 15th, and individual early areas began planting on April 3. However, after sowing, it encountered continuous low temperatures. According to the data from Gongzhuling Meteorological Station, the average temperature of 10cm in the middle and late April was 8.80°C. Under suitable conditions of soil moisture, soil temperature is the main factor that determines the length of seedling emergence. Soil temperature is greater than 70°C and seeds germinate. Seeds emerge at 16-18°C for 8-10 days. If the soil temperature is 10-13°C, emergence will need to occur. 18 ~ 20d; soil temperature at 21 °C only 5 ~ 6d can emerge. The earliest period of infection by Sphaerotheca fuliginea is from the onset of seed germination to the one-leaf stage, ie, the germination of the seed to its emergence. This year's meteorological conditions prolonged the time from seed germination to emergence, and increased the chance of infestation by smut. 2.4 Farmers lack common knowledge about the scientific use of seed coating agents When farmers buy seed coating agents, they lack knowledge of popular science and are misled by the promoters. Blind use of seed coating agents is also the main reason for the occurrence of smut fungus. Dingjia Village, Mengjia Township, Hulan County, Heilongjiang Province planted a high susceptibility variety, Baidan 31. The seed coating agent used was 20% Fokker seed coating agent produced by Harbin Longzhi Agrochemical Co., Ltd. Head smut chemical composition. As a result, head smut occurred, and the average incidence rate in the area of ​​nearly 33.3 hectares was over 60%, resulting in heavy losses. 3 Prevention and control countermeasures Based on disease-resistant varieties, chemical prevention and control is the comprehensive prevention and treatment technology supplemented by agricultural health cultivation measures. 3.1 Breeding disease-resistant varieties for planting From the perspective of long-term goals and sustainable control, the basic work for prevention and control of head smut should be the breeding of disease-resistant varieties. The disease resistance of maize to head smut is mainly the nucleus heredity, which is controlled by micro-effect polygenes and is inherited from quantitative traits. The resistance of maize hybrids was mostly between the parents. In crossbreeding, high-resistance inbred lines should be used as parents, and high-sensitivity materials should not be used. When parents with good trait inbred lines are used as parents, they must be combined with high-resistance materials. For the evaluation criteria of resistance to head smut, it is recommended that artificially inoculated head smut should be identified as having a 10% limit of resistance and a natural field identification of 5%. Strictly review and approve varieties and eliminate the circulation of highly sensitive products in the market. At present, the varieties that have better resistance to head smut are Jidan 156, Jidan 159, Jidan 131, Jidan 180, Jidan 342, Jidan 136, Sidan 105, Sidan 19, Pingan 18. Peace 28 and so on. 3.2 Strengthen agricultural health care and cultivation measures to reduce the time of sowing bacteria source sowing, avoiding low temperatures, reduce the chance of pathogen infection. When the disease is not formed, the tumor is promptly removed and carried deep outside the field to reduce the spread of pathogens in the field and retention in the soil. 3.3 Chemical control The use of seed coating agents is one of the most direct, economic, and effective measures for controlling smut in corn. There are many varieties of seed coating agents on the market today. The different control targets for corn pests and diseases are one- and multiple-component formulations, so they must be used selectively. According to a large number of experimental studies, it has been demonstrated that seed coating agents containing decyl alcohol, pentamyl alcohol, and triterpene alcohol components have a significant effect on the control of head smut. Control efficiency up to 87% to 96%. However, phytosterols are susceptible to phytotoxicity when they are sown at a depth of more than 3 cm at low temperatures. The growth of stems in the ground is inhibited, and the bud arches are not excavated and bent, and the cotyledons are deployed underground. This year, such phytotoxicity occurred in the northern areas of Yushu City and Gongzhuling City in Jilin Province. Therefore, when using a seed coating agent containing an olefinic alcohol component, timely sowing is required to avoid low temperatures, and the sowing depth cannot exceed 3 cm. With regard to the problem of phytotoxicity of enechol alcohols, relevant experts are conducting in-depth studies and hope to solve them in the near future. In contrast, there are no safety issues with the pentamidine and triterpene alcohols. Jionong No. 4 seed coating agent produced by Jiong Hi-tech Development Co., Ltd. Pesticide Branch Company is a three-component seed coating compounded by Carbofuryl, Fumei Shuang, and Triterpene Alcohol. The black insect double seed coating agent produced by Co., Ltd. is a binary seed coating agent that is compounded by carbofuran and pentamyl alcohol. These two kinds of seed coating agents are currently used to prevent corn seedling disease, underground pests, and silk in the domestic market. The best agents for smut and corn-bush seedlings have the features of comprehensive control effect and high safety. In short, the use of disease-resistant varieties, selective use of seed coating agents and improved sowing quality, and strengthening of field management can effectively control the occurrence and harm of corn head smut.
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