New characteristics of the seven major diseases of wheat and comprehensive prevention strategies

1 wheat scab

The prevalence of wheat scab in the past 60 years mainly occurred in 2010 and 2012, and the moderate epidemic mainly occurred in 2013-2016. In 2017, the national wheat scab is mainly caused by severe disease in Hubei, Anhui and other areas along the Yangtze River; the susceptible varieties along the Huaihe area are heavier; other areas have milder incidence. Wheat scab has a serious impact on crop yield, generally reducing production by 10% to 20%, and in severe cases by 80% to 90%.

1.1 Occurrence area

Wheat scab mainly occurs in rainy and humid climates in the world, and the middle and lower reaches of the Yangtze River in China are the frequent areas of wheat scab. In recent years, with the change of farming system, such as the increase of population density, the promotion of susceptible varieties and the increase of straw returning area, the occurrence of wheat scab has a tendency to expand. The area along the Huaihe River has become a re-emergence area for wheat scab.

1.2 Toxins produced by Fusarium graminearum

Fusarium graminearum can produce a variety of toxins, such as deoxynivalenol (DON), Fusarium oxysporum (NIV), and zearalenone. DON can cause animals to refuse to eat, can cause vomiting after eating (also known as "vomiting toxins"), and can also lead to crop immunity and teratogenicity. Zearalenone can cause abortion in pregnant females. The limit of DON in wheat and corn issued by the Ministry of Health and the National Standardization Administration of China is 1 mg/kg.

1.3 Causes of increased disease

1.3.1 Amount of bacteria

In the middle and lower reaches of the Yangtze River, from late March to mid-April, the rate of assemblages of rice stalks is 2% to 10%, which is higher than the 1% epidemic index.

1.3.2 Variety disease resistance

Ningmai, Yangmai and Zhenmai series are relatively resistant varieties, and most of them are susceptible varieties.

1.3.3 Climatic conditions during heading and flowering

Diseases may be prevalent if the temperature is above 15 °C for 2 to 3 consecutive rainy days. At present, the amount of population in the wheat field is increased, the canopy density in the field is high, and the humidity in the canopy is high, which will increase the incidence of wheat scab.

Researcher Chen introduced that after the straw was returned to the field, the amount of straw on the surface increased, the amount of bacteria increased significantly, and the production of the capsule and the release of spores were promoted, which increased the risk and extent of the disease. With the promotion of straw returning measures, the influence of bacterial amount is gradually decreasing. In addition, in recent years, the wheat sowing period has been gradually pushed back, and the maturity period has been postponed, resulting in the late temperature conditions more likely to induce scab.

1.4 Chemical form of Fusarium graminearum

According to the difference in toxin-producing types, it can be divided into three chemical types: 3-AcDON, 15-AcDON and NIV chemical forms. Among them, 3-AcDON chemical type strain has the strongest pathogenicity and toxigenic ability.

The Fusarium graminearum from China's warm regions is 3-AcDON, and the Fusarium from cold areas is generally 15-AcDON. The Huainan and Huai Mai areas are mainly 3-AcDON.

1.5 Comprehensive control of wheat scab

1.5.1 Agricultural prevention and control

Due to the inability to achieve wheat planting rotation, the density of the field population is difficult to decline. It is recommended to plant at a proper time to avoid late planting. Improve straw returning technology to reduce straw residue on soil surface.

1.5.2 Resistant varieties

Resistant varieties can reduce the pressure of prevention and control in the later period. The national district test susceptible varieties were rejected by one vote. The requirements for Jiangsu wheat certification are as follows: Huainan area, southern Huaihe area should try to use medium-resistant varieties, and Huaibei area should not choose high-sensitivity varieties, try to use resistant varieties.

According to researcher Chen, the more stable varieties include Yangmai No. 158, Yangmai No. 14, Ningmai No. 9 and Ningmai No. 13. Huaimai No. 20 and Zhengmai 9023 are recommended along the Huaihe variety, and their control effect is slightly better.

1.6 Chemical control of wheat scab

1.6.1 Chemical control strategy

Take precautions and grasp the appropriate period.

1.6.2 Proper control period

In the early stage of Yanghua, "see the flowers to fight" and "play in the rain", the second time around 5 days.

1.6.3 Water consumption, control equipment

The recommended water consumption is 450 L/hm2. The mist control machine in the control equipment has the best control effect.

1.7 Domestic commonly used fungicide products

The cyanobacterial effect is stable. Cyanolide and tebuconazole can simultaneously control scab and powdery mildew. Carbendazim or carbendazim-containing fungicides have lower costs and treat powdery mildew. In recent years, a series of formulations containing tebuconazole have been registered, and the low content of tebuconazole (<10 g) is not satisfactory. A methoxy acrylate (QoI) fungicide promotes the production of toxins.

Researcher Chen introduced that more than 200 varieties currently registered by the Ministry of Agriculture, 90% of which are carbendazim-containing compounding agents, have been used since the 1970s and 1980s, and have the advantages of good effect and low cost. However, the frequency of resistance has risen. In Jiangsu Province along the Yangtze River and along the Huaihe River region, such as Anhui, the pathogens have begun to develop resistance in recent years, resulting in an increase in the amount of medication and an increase in the number of medications. Dr. Chen suggested that the drug resistant to carbendazim should be replaced with a drug such as tebuconazole or mixed. He stressed that it is impossible to achieve effective prevention and control of wheat scab by relying on pharmacy or relying on varieties. It is necessary to comprehensively control "species + pharmacy" to effectively realize the comprehensive prevention and control of wheat scab.

2 wheat powdery mildew

Wheat powdery mildew is one of the most common diseases in wheat in China, mainly affecting leaves, and in severe cases, it also damages leaf sheath, stem and ear. Typical symptoms are the presence of villous hyphae on the surface of the leaves, covered with a layer of white powdery mildew, ie conidia. When the wheat matures, there is a small black spot on the lesion, which is the sexual generation of the powdery mildew.

2.1 pathogens

The original state of wheat powdery mildew is Blumeria graminis, belonging to the genus Ascomycetes, and the wheat-specific type (Blumeria graminis f.sp. Tritici). The asexual state of the pathogen is Oidium monilioides Nees.

2.2 Climatic factors in the prevalence of wheat powdery mildew

The optimum temperature for the occurrence of wheat powdery mildew is about 17 °C, which is not resistant to high temperatures. The growth of wheat powdery mildew pathogens does not require high humidity. The relative humidity can grow from 0 to 100%. The relative humidity is higher and suitable for growth. The conidia are sensitive to ultraviolet light and direct sunlight. Wheat powdery mildew disease is prosperous and light rain during the epidemic season. Short-term heavy rain is not good for the epidemiology of powdery mildew. The main reason is that spores are not resistant to heavy rain.

2.3 The occurrence of wheat powdery mildew

In the past two years, there have been widespread epidemics in all parts of the country, including Huaibei and coastal areas. The incidence of some areas is the heaviest in the past 10 years. Many of the field wheat functional leaves are damaged. Many fields of powdery mildew even extend to the panicles. on. The effect of chemical control in many areas is not satisfactory. In winter, the temperature is high, and the spring is rainy and rainy. It occurs early (more than 20 days earlier than in previous years), and it has been severely affected in the middle and late April.

2.4 Prevention and treatment of wheat powdery mildew

2.4.1 Agricultural control measures

Planting resistant varieties, Yangmai and Zhenmai series varieties are relatively resistant to diseases, and can be planted according to local conditions; rational application of nitrogen fertilizer, improvement of ventilation and light transmission conditions in the field, and reduction of field humidity.

2.4.2 Chemical control period and control indicators

The focus of this measure is to protect the upper functional leaves, from the booting to the flowering stage. When the upper half of the three functional leaf disease leaves rate is about 5% or the diseased plant rate is about 15%, it should be controlled. In the early spring, the rate of 5% of the diseased plants can be controlled to reduce the pressure of prevention and treatment in the later stage.

Researcher Chen said that the prevention and treatment effect of powdery mildew "one spray three prevention" is not satisfactory, and the drug can be used to achieve better control effect at the beginning of the disease. Therefore, it is necessary to strengthen the monitoring of the disease, and the early application of the disease should be carried out in advance. In recent years, the amount of triazole pesticides has increased, and the bacteria have produced certain resistance, and can be rotated for drugs such as ether oxystrobin. Dr. Chen recommended that the control agent be triadimefon (active ingredient dosage 150-180 g/hm2), propiconazole (active ingredient dosage 120-150 g/hm2) and triazole fungicides such as flucyclazole. Esterase and other mildew have a good effect on powdery mildew, but because of its resistance, the planting season is used only once.

3 wheat rust

3.1 wheat rust pathogen

Rust is an obligate living parasitic fungus that relies entirely on obtaining nutrients from living host cells for growth and reproduction. Wheat rust is attributed to Puccinia. Wheat rust is divided into leaf rust (brown rust), strip rust (slip rust) and stem rust (black stem rust). The pathogens are P. triticina and P. striiformis f. sp. Tritici and P. graminis f. sp. Tritici, the symptoms presented are "strip rust, leaf rust, stem rust is a big red spot".

3.2 Wheat leaf rust

Among the three rust diseases, wheat leaf rust is the most widely distributed, and occurs in wheat growing areas all over the world. The southwestern and Yangtze River basins in China are heavier.

3.2.1 Symptoms of the disease

Leaf rust is mainly harmful to wheat leaves, and many scattered, irregularly arranged, round to elliptical orange-red powder blister (the urediospores of pathogens) are formed on the leaves, and elliptical black teliospores are produced under the epidermis of the leaves at the later stage. heap.

3.2.2 Infection cycle

The spore-type parasitoid can produce urediospores, teliospores, borneospores, rust spores and spores. The pathogen can be transferred to the main parasitic on the pine grass. In China, the pathogens complete the infection cycle by the urediospores. Summer spores invade wheat autumn seedlings, wintering on autumn seedlings, and re-infestation in spring. After the wheat is harvested, the bacteria are over the summer on the self-produced wheat seedlings.

3.2.3 Law of occurrence

Leaf rust has a wide range of adaptation to temperature. The occurrence and prevalence of diseases are related to the disease resistance of the varieties, the pathogenicity of the pathogens, the over-summer wintering and the spring rainfall. The spring rain is more and the humidity is more favorable to the disease.

Researcher Chen stressed that in recent years, wheat leaf rust has increased in Jiangsu Province, and the incidence period is generally later than powdery mildew. In the event of heavy rain, it is often more serious than powdery mildew.

3.3 Wheat strip rust

3.3.1 Hazardous parts

The damage of wheat stripe rust is mainly caused by leaves, and the sheath, stem and ear can also be damaged.

3.3.2 Characteristics of the disease

Wheat can be damaged from the seedling stage to the adult stage, and a large number of yellow powder blister (siasporium heap) is produced on the damaged leaves, and the adult stage is arranged in a strip shape parallel to the veins. In the later stage, black powder blister grows in the same part. The summer spores are fresh yellow, narrow to long oval; the winter spores are long and narrow, buried under the epidermis and stripped.

3.3.3 China's popular fauna

The central and eastern regions are the most prevalent fauna of wheat stripe rust in China, accounting for 80% of the wheat area; Yunnan's epidemic fauna includes high altitudes in central Yunnan, western Yunnan, northwestern Yunnan and southwestern Yunnan; Xinjiang's endemic fauna include Yili, Aksu, and Kashgar. And other areas.

Researcher Chen said that the Susong area belongs to the epidemic system in the central and eastern regions, but it is far from the source of the bacteria. It is not seen in the general years, but it has also occurred in some areas in the past two years.

3.4 Prevention and control of wheat rust

3.4.1 Disease resistant varieties

In the southwestern wheat area, varieties resistant to stripe rust are selected, and most of the varieties approved in the upper reaches of the Yangtze River are resistant to disease. There are few studies on resistant varieties of leaf rust, and most of them currently have leaf rust.

3.4.2 Chemical control

(1) The source of stripe rust fungi can be mixed with triazoles and resistant varieties.

(2) In the winter-producing area, take the prevention and control measures of “taking drugs to detect and discover a little control” for the key affected fields, and timely control the disease center.

(3) Provide the control of the wheat field to prevent the spread of the disease area. The monitoring was strengthened on a large area, and the diseased leaf rate was 5%.

Researcher Chen said that the best period of wheat leaf rust is in the early stage of the disease, and it is recommended to use a drug similar to powdery mildew.

4 wheat sheath blight

4.1 Incidence factors

Early sowing, humidity, soil type and sowing amount are important factors affecting the pathogenesis of wheat sheath. The humidity is the dominant factor in spring incidence, and the rainfall in early March to early May is closely related to the degree of disease.

Researcher Chen explained that the early onset of the disease is serious, the Huaibei wheat area is early, and the Huainan wheat area is dominated by spring. The sheath blight in the sandy loam area is heavier than the clay area, and the clay area is heavier than the saline-alkaline soil area. Neutral acidic soils are more severe than alkaline soils. When wheat is planted in large quantities, wheat sheath blight is seriously ill.

4.2 Control strategies for wheat sheath blight

(1) Based on agricultural control, such as appropriate late sowing, controlling the amount of seeding, controlling the amount of fertilizer applied in the early stage, increasing the application of phosphorus and potassium fertilizer, and reducing the humidity in the field.

(2) Select resistant (resistant) disease varieties, such as Ningmai 9 and Ningmai 13 etc.

(3) In the early sowing area, the pesticide seed treatment and coating were carried out to reduce the peak incidence before winter.

(4) In the early spring, the spraying of chemical sprays is carried out to control the development of diseases and reduce losses.

The researcher recommended by Chen is: tebuconazole, difenoconazole, thiazolamide, etc., which have good control effects on wheat sheath blight.

5 wheat total erosion

Wheat total eclipse is a disease with a long history and a wide distribution. It is currently occurring in Shandong, Henan, Hebei, Shaanxi, Hubei, Anhui, Jiangsu and other provinces. In 2016 and 2017, Fuyang and Suzhou in Anhui Province were seriously affected.

5.1 Wheat total pathogens

Most of the total pathogens in China are wheat varieties G. graminis var. tritici (Ggt).

The main source of primary infection of the pathogen is the dormant mycelium on the root of the disease, which has a degenerative phenomenon (TAD), that is, after the disease occurs from 3 to 5 years, the risk of the disease will decrease.

In addition to harming wheat, pathogens can also harm grass crops and grass weeds such as barley, rye, corn, millet and oats.

5.2 Pathogenesis of total eclipse in wheat

Temperature, relative humidity, pH, and aeration conditions are all important factors affecting the incidence of total eclipse in wheat. The temperature is 12-18 ° C, the relative humidity is 80% to 90%, the pH value is 7-8, the ventilation condition is good, and the virus is vulnerable to viruses. Infected, its pathogens are not resistant to high temperatures and sensitive to CO2.

5.3 Prevention and treatment of total erosion

5.3.1 Disease-free area to prevent disease transmission

It is necessary to pass the quarantine of the place of production and carry out the seed dressing in the breeding field. At present, the diseases in the wheat areas of Huanghuai and the middle and lower reaches of the Yangtze River have basically occurred. The large-scale inter-regional operation of agricultural machinery may be the main way to expand the disease.

For sporadic diseases, it is necessary to pull out the diseased plants in time and bring them out of the field for burning; for larger disease centers, sorghum harvesting, and after harvesting, pull out the wheat bran and burn it on the spot. Soil treatment is carried out on the epidemic point and the surrounding soil using a fungicide. If there are germs in the field, the possibility of completely killing the bacteria is extremely small.

5.3.2 Agricultural control of total erosion

There is little difference in disease resistance between varieties; in areas with conditions, water-and-dry crop rotation or replanting of non-host crops, such as rapeseed, potato, garlic, etc.; deep tillage (30-40 cm) to change soil, reduce the amount of soil tillage, It is also possible to return the straw to the soil and strictly suppress it.

5.3.3 Chemical control of total erosion

Chemical control of total eclipse includes both seed treatment and soil treatment.

According to researcher Chen, the seed treatment recommended 125 g/L silazepam suspension seed coating 200 mL/100 kg seed, which can only be used for wheat total etch; 30 g/L difenotropine suspension seed coating agent 500 mL/100 kg seed, this treatment can not only prevent and cure wheat total eclipse, but also control wheat sheath blight; 25 g/L fluke nitrite suspension seed coating 600 mL/100 kg seed treatment can prevent wheat total etch disease And wheat root rot. The soil treatment was carried out by using 50% carbendazim wettable powder at 15 to 30 kg/hm2 and 20 to 30 kg of fine soil before planting, and evenly applied into the seeding ditch.

6 Fusarium stem rot

6.1 Disease performance

(1) Seedling stage: the bud sheath and leaf sheath of the stem base become brown, and the root crown and root of the wheat become brown.

(2) Adult stage: the leaf sheath and the stem base form a yellow-brown to gray-yellow vertical strip. Upper leaf sheaths and stem segments often have brown lesions.

(3) When the humidity is high, a pink mold layer will appear on the bases 1 and 2.

6.2 Disease occurrence factors

(1) Soil conditions: The incidence of poor water and fertilizer management is heavy, the salinity is heavy, the drainage is poor or the slope is heavy.

(2) Climatic conditions: The drought process at jointing and heading stage aggravates disease performance.

6.3 Disease prevention

The control of the stem rot of Fusarium oxysporum mainly includes the selection of resistant varieties and control agents. Researcher Chen said that some varieties in foreign countries have good resistance to diseases, and there are differences in domestic resistance. It is recommended to use disease-free seeds and seed treatment. A coating agent such as sputum nitrile (for funeral) or tebuconazole may be used. The application of fungicides at jointing stage also has a certain effect on the control of dead white ears.

7 Wheat yellow mosaic disease

7.1 Occurrence and symptoms

Wheat yellow mosaic disease, also known as wheat spindle mosaic disease, the pathogen is wheat yellow mosaic virus (WYMV), and the mediator is the soil polymyxa in the soil. Jiangsu occurred sporadically in the 1970s. In the 1980s, the venom of diseased fields accumulated. It has spread rapidly since the 1990s and is widely distributed along the Yangtze River, the southern hills, and the Lixiahe area. The average disease field is reduced by 10% to 50%, and the severe cases are not harvested.

No symptoms appear before winter, and symptoms appear when the young wheat grows back in early spring. At the beginning of the disease, the new leaves of the diseased plants showed chlorotic to necrotic fusiform streaks, which were interspersed with green tissue and became mosaic symptoms. Later, the spread of lesions increased, which could lead to yellowing and deadness of the whole diseased leaves, dwarfing and tillering of severely diseased plants. cut back.

In the field with lighter incidence, the temperature of the disease increased more than 15 °C in the later stage, and the disease in the field gradually became hidden. After heading, the diseased field recovered faster, but it was still shorter than the healthy plant, uneven, small and large. deformity.

7.2 Disease prevention

(1) Comprehensive agricultural prevention and control measures based on the promotion of resistant varieties and combined with rational water and fertilizer management.

(2) Rotation, and non-host barley, rapeseed and other rotations.

(3) Appropriate late broadcast, avoiding the optimal period of mediator infection.

(4) Rational fertilization, early application of quick-acting nitrogen fertilizer, phosphate fertilizer and growth regulator to promote the growth of wheat seedlings.

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