Seedling blight is an important seedling disease of maize. It is caused by a variety of fungi such as Fusarium oxysporum, Fusarium oxysporum, Fusarium graminearum, and Rhizoctonia solani. A general term for the decay of corn roots or near-stem tissue. The incidence of seriously ill fields is as high as 30% to 40%, and some fields are seriously lacking in seedlings and ridges, and even destroyed.
Identification point
Maize seedling blight can be manifested from the 2 leaf 1 heart stage, mainly in the middle and late May, and the corn grows 4 to 7 leaves.
1 The seed begins to produce browning at the root and root tip of the seed, and then spreads to the whole root system. The root hair begins to appear pale yellow to yellow brown infection point, and becomes yellow-brown water-stained necrosis after 1 to 2 days. The cortex rots, the root hairs fall off, there are no secondary roots or few secondary roots, and the stem base is immersed in water. The diseased plant is pulled up, and white, grayish white or pink mildew, that is, conidiophores and conidia of the pathogen, sometimes appear in the affected part of the root.
2 The leaf sheath of the leaf became brown and torn, the leaves turned yellow, and the leaves showed yellow-brown dead streaks, which showed a dead focus, and the heart leaves were curled and easily folded. Later, the leaves gradually dry up from the bottom up, and the dead seedlings have no secondary roots, and a small number of secondary roots form weak seedlings. There is no obvious symptom in the upper part of the seedlings that are harmful to light. Generally, it occurs in the corn leaf stage to the heart leaf stage, and begins to yellow at the tip of the first leaf and the second leaf, and gradually develops to the middle of the leaf. Serious individual leaves or plants appear wilting, after 3 to 5 days. The leaves turn blue or yellowish brown.
Law of occurrence
There are many sources of initial infection of corn seedling blight, and the causes of the disease are more complicated, mainly including:
1 sick body and soil belt. Continuous cropping is the main cause of sickness and soil contamination. According to the survey, the incidence of seedling blight in the field of continuous cropping for 1 to 3 years is 7.1%, 11.6%, and 15.9%, respectively. The cause of serious crops in the continuous cropping field is mainly due to the proliferation of Fusarium residual soil and diseased plant residues. Accumulation, so that the soil pathogen base increased year by year. Secondly, due to the selectivity of nutrients absorbed by the same crop, the nutrient elements in the soil showed physiological imbalance. According to the measurement, the total amount of nitrogen, phosphorus and potassium in the soil did not change much with the increase of continuous cropping years, but the available zinc The content of boron is reduced by a factor of two, and the content of hydrolyzed nitrogen and available potassium is significantly reduced, with an average reduction of 15 to 17 mg/kg. Therefore, the plant disease resistance is significantly reduced.
2 seeds with bacteria. This is the main reason why the seedling disease occurs early and can form a central disease strain. The surface of the seeds was separated and monitored after disinfection with 0.2% mercuric mercury. The seed carrier rate averaged 0.5% to 3.5%.
3 fertilizer with bacteria. In recent years, farmers have reduced the amount of organic fertilizer applied to the land, and some have applied unfertilized fertilizer. In the corn producing areas, pig and livestock forage materials are mostly smashed with corn stalks and grains as the main raw materials. After the experiment, the seedlings were collected and added to the cattle feed for 2 days, and the feces were collected. The rate of corn seedlings was 6.4%~13.5% without fermentation and fertilization. Therefore, the fertilizer carrier was also the main cause of the seedling blight. one.
4 the land is not flat. The soil is low in the low-lying water and from the field. The main reason is that the soil is sticky, the temperature is low and the soil moisture is high, which is not conducive to the development of the roots of the seedlings and the disease resistance of the plants is reduced.
5 The relationship between disease and climate. The temperature is higher, the emergence is fast, the growth is prosperous, and the incidence rate is low; the rainy days are more, the soil temperature is low, and the incidence rate is high.
Control method
There are many ways of infecting corn seedling blight at the beginning, the disease is early, the plant death rate is fast, and the control is difficult. Therefore, it is necessary to conduct comprehensive prevention and control based on agricultural measures and seed disinfection.
1 use resistant varieties.
2 rounds of dumplings should be arranged as reasonably as possible, and non-corn corn crop rotations, especially in the depressions after wheat and corn strips, it is necessary to scientifically arrange the front wheat strips for small dumplings.
3 Deeply smashing the cockroaches, leveling the land after the corn is harvested, it is necessary to deepen the cockroaches in time, promote the decomposition of the diseased bodies, inhibit the propagation of pathogenic bacteria, and reduce the amount of soil bacteria. Pre-sowing should be finely grounded to prevent [water from ], promote root development and enhance plant disease resistance.
4 Rational fertilization, strengthen cultivation management and increase the application of decomposed organic fertilizer. It is strictly forbidden to apply unfertilized fertilizer, block the route of fertilizer and reduce the incidence. After the rain, timely stroke, break the soil compaction, enhance soil aeration, promote root growth and development, and improve disease resistance.
5 seeds were sterilized for 1 week before sowing, and inoculated with 50% carbendazim WP 800 times or 40% sodium chloroisocyanurate f carbendazim for 600 minutes, dried and then sown. Or use 1 part of the antibacterial agent to add water to 20 parts of the leachate, soak the seeds for 12 hours, so that it can prevent disease and increase seedling production. It can also be used with 500% of the bacteriocin seed coating agent or 50% carbendazim WP, which has good control effect.
6 seedling transplanting and seedlings to raise seedlings to transplant seedlings to replant seedlings, to solve the lack of seedlings and ridges formed by seedling blight. The method is to arrange the seedbed or prepare the nutrient meal when the corn is planted. In order to reduce the production cost, the nutrient meal can be made of old plastic or kraft paper, and the specifications are 7-8 cm in diameter and 8-9 cm in height. The seedbed soil and the substrate are mixed with sieved slag and river sand 3:1, and the appropriate amount of decomposed organic fertilizer is added and mixed in the bed and the body, watered, and the seeds are sterilized after 2 to 3 days. When transplanting, it must be transplanted with soil (or matrix), watering in time, absolutely can not damage the roots, resulting in slow seedlings, otherwise the plants can not develop normally, affecting the mixing time and yield of pollination.
7 timely spraying in the field after emergence of wilting diseased leaves or individual diseased plants, should be sprayed and controlled, 50% carbendazim WP 500 times solution, or 72% cymoxan Mn Mn Zn WP 600 Double solution, 58% metalaxyl manganese zinc wettable powder 500 times solution, spray evenly.
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