In recent years, with the increase of continuous cropping corn, diseases such as black silk and ear of corn have been spreading and aggravating, and some areas have become serious diseases in current corn production, which has brought certain difficulties to the production and life of some farmers. To this end, the symptoms, causes and prevention measures of corn smut are introduced as follows:
First, the symptoms
The pathogen of corn smut is corn sphaeroides, belonging to the genus Basidiomycotina, the genus Aspergillus, the genus Phytophthora, and the genus A. The head smut disease harms the ear and the tassel, forming a bacterium. The sputum is filled with the teliospores of the pathogen, and the residue of the filamentous vascular bundle remains, hence the name "Silk smut".
Some of the diseased plants have no spiro filaments, short and fat shape, thick base, sharp tip, and complete scorpion leaves, but the inside of the ear is filled with black powder, which is the teliospores of the pathogen. Later, the temporal lobe ruptured, revealing black powder, and the black powder was more bonded into a block, which was not easy to fly. The black powder is sandwiched between filamentous corn vascular bundles. In addition, the diseased ear loses its original shape and is severely deformed into a "hedgehog" shape.
There are two types of symptoms in tassel incidence: First, a single spikelet on the tassel becomes a bacillus. At this time, the flower is deformed and does not form stamens. The glume becomes leafy due to stimulation, and the base of the male flower is enlarged and contains black powder. Second, the entire tassel becomes a large bacterium, and the outer bread is covered with a white film. After the film is broken, the black powder is exposed. Black powder is often bonded into a block and is not easily dispersed.
Most of the early-stage plants showed symptoms in both ear and tassel, and only the ear of the late onset showed symptoms, and the tassel was normal. Most of the plants with tassels have no ears.
In addition, a variety of whole-plant symptoms can occur in the corn seedling stage. Some diseased plants are short, curved, with leaf clusters, dark green leaves, yellow-white streaks on both sides of the ribs in the leaves; some internode shortening, plant dwarfing, leaf clumps, increased ear, and each leaf axillary grows Black spikes; some tillers are abnormally increased, and black spikes grow at the top of each tiller. The symptoms at the seedling stage are variable and unstable, and may change due to different varieties, pathogens and environmental conditions.
Second, the cause of the disease
(1) High pathogen base
1. Soil bacteria: According to the survey, most of the diseased fields are corn for many years, and the continuous cropping period is more than 3 years. Continuous cropping of corn makes the smut of corn smut that can survive for 2-3 years in the soil accumulate, causing a large amount of bacteria in the soil.
2. Fertilizer-bearing bacteria: In recent years, some farmers have improperly treated the corn stalks in the ward, causing the fertilizer to carry bacteria.
(1) Feeding the livestock with the straw with the bacteria, and the smut of the smut is still able to survive after the stomach of the animal, causing the manure to be carried.
(2) Using the straw with fertilizer, without being fully decomposed, the spores are still viable.
(3) Straw directly returned to the field, although the soil fertility was improved, but the bacteria were all returned to the field with the plants.
3. Improper treatment of diseased plants: some farmers failed to remove the diseased plants in time; some of the diseased plants were randomly stacked in the field; some farmers only paid attention to the removal of the diseased tassels, while ignoring the diseased ears; The farmer randomly placed the diseased plants into the bullpen. These practices have increased the amount of bacteria in the field to varying degrees.
(2) Low resistance of varieties
The disease resistance of maize varieties varies greatly. Under the same inoculation conditions, the rate of diseased plants of highly susceptible varieties can reach more than 80%, while that of medium resistant varieties is only 50%-10%, while that of high resistant varieties is only 5%. Planting the same variety on a large scale throughout the year is the main cause of the occurrence of smut.
(3) High temperature and drought in spring
In the case of more soil bacteria and planting susceptible varieties, the soil temperature and humidity after sowing (the soil temperature is mainly determined by the sowing date) becomes the dominant factor determining the number of invasive bacteria. In the range of 13 °C-35 °C, the pathogens can infect, 16 °C-25 °C is suitable for infection, and the infection rate is the highest at 22 °C. Soil moisture is moderately dry to facilitate intrusion. In the case of low temperature and drought during spring sowing, the emergence time of corn is long, and the growth of seedlings is slow, which will create more infection opportunities for pathogens. In addition, the poor quality of the land preparation, loss of the block, will also lead to soil dryness, creating favorable conditions for the invasion of pathogens.
Third, prevention measures
Comprehensive control measures should be taken to prevent and control corn smut. The cultivation of disease-resistant varieties and the reduction of field bacteria are mainly supplemented by improved cultivation management measures and seed treatment.
(1) Selection of high-quality resistant varieties
The selection of resistant varieties is the most fundamental measure to control silk smut. All farmers should choose disease-resistant varieties in combination with the actual, and at the same time choose new seeds with full particles, so that the corn emerges quickly, grows vigorously, and is not susceptible to disease.
(2) Reducing the source of field bacteria
1. Rotation: Stop the planting of corn in the ward, combine the adjustment of the planting structure, and implement the rotation of corn and beans, potatoes or melons and vegetables for more than three years to avoid the disease worsening due to continuous cropping or unsuccessful.
2. Fertilizer treatment: no corn stalks are used as feed; manure is fermented at high temperature, fully decomposed, and sprayed with chemicals; stop the straw returning to the field or clean up the diseased plants before returning the straw to the field.
3. Removal of diseased plants: typical symptoms in the seedling stage, combined with weeding to eliminate diseased and suspicious seedlings before seedlings. When the seedling stage does not show symptoms or the symptoms are not easy to identify, when the flare is obvious, the diseased plants are cut off in time. After the corn is headed, the diseased plants are cut off in time before the telioses in the sputum are mature and scattered. The diseased tissue after corn harvest should be treated in time to reduce the bacterial source.
(3) Improving cultivation management measures
1. Adjust the sowing date and improve the quality of sowing: select seeds before sowing, and soak the seeds to increase the germination potential of the seeds; fine land preparation, appropriate shallow sowing, and under-planting. These measures can promote the rapid emergence of seedlings, the emergence of strong seedlings, reduce the chance of infection of pathogenic bacteria, and improve the disease resistance of plants.
2. The mulching technique is adopted: the mulching film can increase the ground temperature, maintain the soil moisture, and accelerate the emergence and growth of corn, thereby reducing the chance of disease.
3. The use of bauxite rooting technology: in the seedlings from one heart to the second leaf and one heart period, the soil around the nursery is opened, so that the seedlings of the seedlings are exposed to the sun, and the soil is restored after 10-15 days, which can reduce the occurrence of diseases.
(4) Chemical control
Insist on the treatment of seeds with pesticides before sowing. The most common seed treatment method is chemical dressing. Seed dressing with fungicide 15% triadimefon WP or 50% thiophanate-methyl WP at 0.3%-0.5% by weight of seed; use 12.5% ​​oxazolol WP or 2% tebuconazole wet seed dressing according to seed 0.2% seed dressing by weight; seed dressing with 0.1%-0.2% of seed weight with 15% myclobutanin EC seed coating, better control effect than triazolone, with sustained release and durability.
(5) Vigorously publicize scientific knowledge, find problems early, solve problems in time, eliminate corn smut in the bud, and avoid serious illness.
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