Maize is one of the major food crops in Heilongjiang Province, with an annual planting area of ​​about 240 hm2. Due to the hazards of corn diseases, the annual output is lost by 10-15%, and when it occurs in large numbers, it is 30-40%. Serious land masses or even no harvests have become the limiting factor in increasing corn yield and quality. There are more than a dozen kinds of common corn diseases in Heilongjiang Province. Due to the popularization and application of corn hybrids, corn leaf spot and corn head smut rapidly become popular and become the main diseases at that time. For this reason, during the "6th Five-Year Plan" period, corn leaf spot disease and corn smut disease were listed as national key research projects. Significant progress was made in the occurrence, epidemics, and resistance of varieties. More than 20 years later, new diseases have emerged, and the types of diseases have increased; diseases that once were once controlled have re-emerged; some minor diseases have risen as the main diseases.
First, the trend of corn disease
1. Once again, the once-to-be-controlled disease broke out again. The epidemic corn smut is the main disease in maize production in our province in early 70s. The hybrids promoted at that time, such as tender Shan No. 3, No. 4 and No. 5, and Long Dan No. 1 and No. 5, were not resistant to smut caused by corn smut, and their planting area accounted for over 50% of the planting area. The large-scale cultivation of susceptible hybrids has led to the pandemic of maize ear smut, which has caused serious losses in corn production. With the application of anti-corn black ear varieties and the use of chemicals, by the mid-1980s, the incidence of corn smut was controlled at 1-2%. Since the 1990s, head smut has re-emerged. In 2001, corn smut was moderately serious. In 2002, corn smut occurred in the province. The survey results of the main maize production areas in Shuangcheng, Acheng, Binxian, Jidong, Wuyuan, and Weizhou counties indicated that more than 50 varieties had spikes of corn silk, and the incidence was due to differences in plots and varieties. In contrast, the average incidence rate is 15-20%, and serious plots are more than 60%, or even out of production. The severely affected varieties include Baidan 19, Longdan 19, and Jidan 197. The wide area of ​​the disease, the degree of harm is not seen in the past.
2. Secondary diseases rise to major diseases
In the 1970s, maize dwarf mosaic disease and corn rough dwarf disease occurred only sporadically in our province, with little harm. As a minor disease, it was not valued by people. In the late 1990s, the incidence of the disease increased year by year, and the annual incidence of individual species exceeded 10%. Maize dwarf mosaic disease and corn rough dwarf disease are transmitted by seeds or insects. It is a systemic disease. Plants are infected early, and the disease of the whole plant can hardly be established, and the yield loss is close to 100%.
Second, the occurrence of disease, epidemic causes of corn disease development is a dynamic evolution process, the process by the natural environment and human factors such as farming systems, cultivation methods, sown area, prevention and control technology and host plant resistance and pathogenic bacteria mutation and many other Constrained by factors.
1. The change of farming cultivation system First of all, greatly increased the sowing date of corn. The large double-closure technology of corn increased the original ridge length of 70cm, and the sowing date was about 15-20 days ahead of the normal sowing date. In the western provinces of Shaanxi Province (Acheng, Shuangcheng, Wuyuan, Jidong) and semi-arid regions in the west and mid-western provinces, farmers often take early sowing for the purpose of grabbing mourning. The earliest sowing period was April 17. Due to the low temperature in early spring, the seeds germinate slowly in the soil and their vitality is weak, which prolongs the time of seedling excavation and provides extremely favorable conditions for the infection of soil-borne pathogens. Secondly, the planting density of maize increased, and the plant types of maize varieties promoted and applied before the 1980s were mostly flat or semi-flat. The planting densities were small. However, the maize plant types currently applied in production are mostly dense compact plants with high planting densities. Increased density and increased humidity have created good environmental conditions for the occurrence and prevalence of airborne diseases. At the same time, fertilization is unscientific, with nitrogen, phosphorus deficiency, and low potassium, resulting in plant growth and resistance to disease. In addition, large-scale continuous cropping of corn, the rhizosphere microflora changes, deterioration of the root environment of maize and large-scale planting of high-yield and high-quality disease-resistant varieties, leading to increasingly serious corn diseases.
2. Single-cultivation of disease-resistant varieties. Single-resistance varieties currently promoted in production have a large area for planting, a single genetic basis, and a weak genetic defense mechanism. At the same time, a large number of virulent species are proliferated, the frequency of pathogenic bacteria increases, and the resistance of resistant varieties is lost. Disease outbreaks are prevalent.
3, plant health measures are not perfect Maize plant tall, after the jointing of the group closed, difficult control, the existing technical measures are poor, control costs are relatively high, a single measure can not achieve people's expected results.
III. Comprehensive management strategies There are many kinds of corn diseases, and the epidemic factors are complex and changeable. The prevention and control methods should be varied. The disease treatment must start from the whole of the agro-ecosystem and transform the single disease prevention and control into the comprehensive prevention and control of the system; and protect the corn. The main direction is to protect the farmland ecosystem, and the integrated prevention and control of the main elements of the ecosystem control and natural control will be developed, and the organic coordination functions of key technologies will be brought into full play.
1. Breeding and utilization of disease-resistant varieties and varieties Rational selection Breeding and utilization of disease-resistant varieties are the most fundamental, economic, safe and environmentally-friendly measures for controlling corn diseases. Screening resistance against the origin of resistance, discovering disease-resistance genes, creating resistance-resistant breeding materials with excellent resistance to agronomic traits, and cultivating new disease-resistant varieties, which will be popularized in production. The rational distribution of the promotion varieties, in the same ecological area, according to a certain percentage of planting different types of hybrids resistant to disease, to avoid the variety of a single planting.
2. Agricultural planting and disease prevention measures should be planted in a timely manner. Maize-soybean and corn-maize rotation should be adopted to change the ecological conditions in the field. Reasonable formula fertilization should be adopted to increase the application of K fertilizer in a timely manner to improve the ability of maize to resist diseases and pests; and to soil-borne diseases. The use of seed coating can achieve a multiplier effect.
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