In recent years, the incidence of seedling blight of summer maize in Shandong has aggravated, which has become one of the major diseases that harm corn production. According to the survey, the diseased plant rate in the general field is 10% to 15%, and the severe land mass is 20% to 50%, which has a great impact on the corn yield. Symptoms: The disease occurs mainly in corn seedlings. The susceptible plant is first browned at one, several, or apical roots of the seed and later expanded into a section or the entire root system, one or more of which may occur at the same time, and then infect the root (messophageal root). The roots were stunted, the root hairs were reduced, there were no secondary roots or a few secondary roots, the primary roots were aged, the cortex was necrotic, the roots became dark brown, and necrotic ring-shaped spots were formed between the first nodes; the stems became water-stained and decayed; Under the action of external forces, the internodes of the basal part are prone to neat breakage; the upper part of the leaf sheath is lacerated, the leaves are yellow, the edges are scotch-like, the heart leaf is curled, and it is easy to fold; afterwards, the leaves gradually dry from the bottom up; no secondary roots The emergence of dead seedlings, the formation of a small number of secondary root formation of weak seedlings, high humidity in the close-to-ground part of the diseased seedlings produce white mold; light damage to the ground without obvious symptoms, generally in the beginning of the second leaf, the first and second The tip of the leaf appears yellow, and gradually develops toward the middle of the leaf. After the head of the shoot section grows out of air and roots, the absorption capacity increases, and it can continue to grow into a key strain, but the leaves of the seriously damaged plant appear to be fiery Dead, leaf gradually R. wilting, stem base rot, gently mention can be pulled up by hand. Pathogens: There are eight kinds of pathogenic bacteria, including Fusarium moniliforme, Fusarium spp., Fusarium graminearum, Helminthosporium, Rhizoctonia solani, and Pythium. Among them, Fusarium moniliforme is the main cause of corn seedling withering. Pathogens, the pathogenic bacteria are weak parasites and generally survive in the soil for 2 to 3 years. Occurrence conditions: 1, climatic conditions: corn seedling blight generally occurs in 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†will lead to its occurrence. According to investigations in recent years, during the period from the time of corn sowing to hair rooting, a sudden rain meets heavy rain to cause soil compaction and cause soil. The environment with low temperature and high humidity is easy to infect the disease, but the land sown after the rain of the same variety is basically not affected, indicating that the degree of disease has a great relationship with the climate conditions. 2. Variety: According to a survey conducted from 1998 to 2002, the currently promoted maize varieties such as Ludan 50, Nongda 108, and Ludan 981 have strong disease resistance in the middle and late stages of growth, but they are weak in seedling growth and their roots are susceptible to seedlings. disease. The main reason for the large area of ​​seedling blight in recent years is the expansion of the parental variety of 178 or Qi319 inbred lines. 3. Soil and management measures: low-lying land, poor soil, heavy land on the clay land, saline-alkali land and corn herbicides, and deep sowing are also prone to disease. 4. Rotation mode: Wheat/maize is the main rotation method in our province. In recent years, the occurrence of wheat root disease has led to the accumulation of pathogenic bacteria such as Fusarium moniliforme, Fusarium graminearum, and Rhizoctonia solani, which has also aggravated corn seedling blight. The degree of occurrence. Prevention and control measures: The prevention and control of corn seedling blight should implement the principle of “prevention from prevention and comprehensive managementâ€. It should focus on breeding and promotion of disease-resistance varieties, and at the same time, make good seed dressing, advocate seed coating, and rationally apply fertilizer. Enhance the cultivation and management of the field, so as to effectively control and reduce the incidence and harm of seedling blight. 1. Rational fertilization and strengthening of field management: Rational fertilization is an important measure for alleviating seedling blight, so it is necessary to apply basic fertilizer, increase phosphate fertilizer, and cultivate strong seedlings when sowing; timely cultivating after corn emergence or rain, in order to facilitate the ventilation of the roots Promote root growth. 2, seed dressing and disease prevention: available 50% carbendazim WP, according to the seed amount of 0.2% to 0.3% seed dressing, Huayang 20% ​​of corn seed coating agent or the use of coated seeds, both insecticidal and strong Miao, more than one at a time. In addition, in the last two years, 25% of new seed coating agents were applied to 0.2% Shilok. The control effect was up to 90%. 3. Seedling blight at the seedling stage can be controlled by methyl-rhizophos-methyl. Generally, a strong root can be grown after 3 days of spraying. One of the following pesticides can also be used to spray the base: 50% carbendazim 600 times, 20% triadimefon 1000 times, evil rot 3000 times, Yumai 400 times, spray twice.
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