In recent years, the occurrence of seedling blight in summer maize in Shandong has increased, and it has become one of the main diseases that harm corn production. According to the survey, the disease rate of the general diseased area is 10% to 15%, and the serious land area is 20% to 50%, which has a great impact on corn yield. Symptoms: The disease mainly occurs in the corn seedling stage. The susceptible plant is firstly browned from one part of the seed root, several places or the root tip, and later expanded into a section or whole root system, one or several pieces can occur at the same time, and then invade the root (medium radicle). Cause root dysplasia, root hair reduction, no secondary roots or a few secondary roots, primary root aging, cortical necrosis, roots become dark brown, and a necrotic ring spot is formed in the first section; the base of the stem is watery and rot; The basal internodes are prone to neat rupture under the action of external force; the upper part of the leaf sheath is brown in tearing, the leaves are yellow, the edges are dead-focus, the heart leaves are curled, easy to fold, and the leaves gradually dry from bottom to top; no secondary roots The dead seedlings are produced, and a small number of secondary roots form weak seedlings. When the humidity is high, white mold is produced in the part of the dead seedlings close to the ground; the lightly damaged upper part has no obvious symptoms, and generally begins at the second and second phases. The tip of the leaf appears yellow, and gradually develops to the middle of the leaf. After the root section of the upper part of the ground grows out of the root, the absorption capacity is enhanced and can continue to grow into a key strain, but the leaves of the seriously damaged plant appear to be burning. Pathogens: There are eight kinds of pathogenic bacteria: Fusarium oxysporum, Fusarium oxysporum, Fusarium graminearum, Helminthosporium, Rhizoctonia solani and Pythium, among which Fusarium oxysporum is the main cause of corn seedling The pathogenic bacteria, which are weak parasitic bacteria, generally survive in the soil for 2 to 3 years.
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Condition:
1. Climatic conditions: Corn seed blight usually occurs from early June to early July. The climatic conditions affecting corn seedling blight are mainly temperature and humidity, and long-term "low temperature and high humidity" is beneficial to it. According to recent investigations, during the period from corn to rooting, the medium is thick and the soil is knotted, causing soil. The environment with low temperature and high humidity is easy to infect the disease, and the plots planted after the rain of the same species are basically not affected, indicating that the degree of disease has a great relationship with the climatic conditions.
2. Varieties: According to the survey from 1998 to 2002, the corn varieties such as Ludan 50, Nongda 108 and Ludan 981, which are currently promoted, have strong disease resistance during the middle and late growth stages, but the seedling stage has weak growth and the roots are extremely susceptible to seedlings. disease. The expansion of the variety of 178 or 319 inbred lines as parents is the main reason for the large area of ​​seedling blight in recent years.
3. Soil and management measures: The terrain is low, the soil is barren, and the plots of clay, saline-alkali land and corn herbicides are heavy, and the sowing is too deep.
4. Rotation mode: Wheat/maize is the main rotation method in our province. In recent years, wheat root disease has become serious, leading to the accumulation of pathogenic bacteria such as Fusarium oxysporum, Fusarium graminearum and Rhizoctonia solani, which also aggravated corn seed blight. The extent of the occurrence. Control measures: The prevention and control of corn seedling blight should follow the principle of “prevention and comprehensive managementâ€. It should focus on the selection and promotion of disease-resistant varieties, and at the same time do a good job in seed dressing, promote seed coating, and rationally fertilize. Strengthen the management of field cultivation so as to effectively control and mitigate the occurrence and damage of seedling blight.
1. Rational fertilization and strengthening field management: Rational fertilization is an important measure to reduce seedling blight. When planting, it is necessary to apply base fertilizer, increase application of phosphate fertilizer, and cultivate strong seedlings; corn should be cultivated after emergence or after rain to facilitate root ventilation. Promote root growth.
2, seed dressing disease prevention: 50% carbendazim wettable powder, seed dressing 0.2% ~ 0.3% seed dressing, Huayang 20% ​​corn special seed coating agent or use coated seeds, both insecticidal and strong Miao, one more. In addition, in the past two years, 25% seed dressing with 25% of the new seed coating agent was applied, and the control effect was over 90%.
3. Seedling blight is found in the seedling stage. It can be prevented by methyl-lipophosphorus. Generally, the roots can be grown after spraying for 3 days. Alternatively, the base can be sprayed with one of the following pesticides: 50% carbendazim 600 times solution, 20% triadimefon 1000 times solution, dioxin 3,000 times solution, jade sterilized 400 times solution, and spray twice.