Misunderstanding of wheat scab

Wheat scab, also known as wheat ear blight, rotten wheat ear and red wheat ear, is one of the main diseases of wheat and one of the more serious diseases at wheat ear stage. Wheat scab is widely distributed all over the world, mainly in humid and semi-humid areas, especially in temperate regions with humid and rainy climate. According to the report of relevant departments, in 20 12, the occurrence area of wheat scab in a province in Huanghuaihai agricultural area was about 24.6 million mu, accounting for 68.3% of the whole province's wheat planting area, which was the highest in the history of wheat scab in this province. Although the production loss was recovered through full prevention and control, it still caused some losses in wheat production, and some farmers reduced production and suffered heavy losses. Wheat scab has become a problem affecting wheat quality. Wheat infected with scab will affect wheat yield and quality. Improper prevention and control will lead to wheat yield reduction, which will lead to serious crop failure. According to media reports, in 20 12, a farmer in an Anhui province harvested the immature wheat infected with scab (confirmed to have stopped production) in advance, and sold the straw to a dairy farm for feeding cattle at the price of 0. 15 yuan/kg. This kind of wheat straw is green and strong, but its ears are withered and white. At the same time, the quality of wheat infected with scab decreased, the grain shrank and the flour yield decreased. Wheat scab not only caused serious yield loss and quality impact on wheat production, but more importantly, its diseased wheat toxin affected food safety and attracted much attention. Fusarium ear blight is caused by Fusarium fungi, which not only causes loss of wheat yield, but also produces mycotoxin (i.e. vomitoxin DON) mainly containing deoxynivalenol, which is harmful to people and livestock. Eating sick wheat can cause acute poisoning symptoms such as dizziness, fever, nausea and diarrhea, and even bleeding in severe cases, which directly threatens the health and life safety of people and livestock. Therefore, the diseased wheat rate in wheat reached 4. 20 12 It was reported by the media that the Grain Management Institute rejected wheat because it was infected with scab. In short, the wheat infected with scab either has no yield or has yield, but the wheat can't be sold and there is no income. In view of the serious harm of scab, farmers attach great importance to it and take a series of measures. According to the report, the control effect is quite different. Through investigation, it is found that farmers' understanding of scab is still insufficient, and there are still many misunderstandings in the prevention and control of scab. One: Be lucky about the occurrence of scab and rely on old experience to solve new problems. Wheat scab is a typical climatic disease, which is caused by several Fusarium fungi. Its occurrence and prevalence are affected by many factors, such as the number of bacteria sources, variety resistance, agricultural ecological environment and cultivation management measures. The epidemic of wheat scab is closely related to meteorological conditions. When the average temperature in spring is above 9℃ and it rains continuously for 3-5 days, the overwintering bacteria will produce ascospores. When there are a large number of mature ascospores at the heading and flowering stage of wheat, when exposed to rain or humid air, the mature ascospores spread on the anthers, and infect the spikelets through filaments, which initially produce soaked light brown spots on the spikelets and glumes, and gradually expand to the whole spikelets. If a certain amount of precipitation occurs for more than three days in the heading and flowering period of wheat, it will cause a pandemic of wheat scab. If it rains for three consecutive days, the rainfall is above 12 mm and the relative humidity of the air in the field is above 80%, which is very beneficial to the release and infection of ascospores. When the air humidity in the field reaches more than 80%, it is very likely to cause the occurrence and epidemic of wheat scab. Therefore, three aspects should be paid attention to in the prevention and control of wheat scab. "Looking at the sky, looking at the seedlings and looking at the ground" needs to comprehensively consider the pathogenic factors. Some farmers failed to comprehensively consider the above factors, failed to fully understand the symptoms, epidemic regularity and pathogenic factors of scab, and only paid attention to weather changes (rainfall and temperature) with reference to old experience, ignoring the influencing factors of field humidity and variety differences. Although no large-scale diseases occurred, they also caused diseases, which affected the improvement of wheat yield and quality. Two: pay more attention to treatment than prevention, take medicine because of illness, and miss the best prevention and treatment period. Wheat scab can be prevented and incurable, and the traditional methods of giving priority to prevention, taking the initiative to defend, emphasizing treatment and neglecting prevention are not conducive to the prevention and control of scab. At the same time, the choice of medication period in the process of disease prevention and control will directly affect the prevention and control effect. According to many data, the medication period of scab disease is "heading stage to flowering stage". For such a long period of medication, the effect of medication varies greatly in different time periods. Some farmers choose to use drugs at the booting stage or the end of flowering, and even after seeing the powdery mildew layer, they do not have a good grasp of the best control period, and the control effect is low. Through field investigation, it was found that the best control period was from full heading to flowering 5%. At the same time, there are several situations to be fully considered. The weather is sunny and the temperature is high at heading stage. When wheat is heading and flowering, it can be used at the full heading stage. The temperature at heading stage is low and there is little sunshine, so wheat should be used at the early flowering stage after heading. When there is more rain than rain at heading stage and scab is easy to spread, it is better to spray it early than late. Don't wait until the weather is fine or the flowers are in bloom, spray it several times to prevent it. If chemicals with good internal absorption and long duration are used, the control period can be advanced to the early heading stage of wheat. Third, the blind choice of chemical drugs ignores the complementarity of drug resistance and mechanism of action. At present, there are 248 pesticides registered in the Ministry of Agriculture to control wheat and wheat scab (as of March 20 13). Among them, carbendazim (97 registration certificates), thiophanate-methyl (50 registration certificates), polyketone (35 registration certificates) and thiram (2 1 registration certificate) accounted for 8 1.85% of the total registration certificates, and the registered control agents involved 14 components. In recent years, farmers have generally reported that carbendazim is ineffective and other pesticides are not effective. It is not excluded that some pesticides have quality problems. We should also consider the relationship between drug-resistant strains, which is also closely related to farmers' careless use of pesticides with different mechanisms in the process of drug use. Spraying benzimidazole fungicides such as carbendazim is one of the key measures to control wheat scab in China since the mid-1970s. It is reported that since the first drug-resistant Fusarium graminearum strain was found in Haining, Zhejiang Province on 1992, it has been tested in Zhejiang, Jiangsu, Shanghai, Hubei and other places for many years, and it has been found that the proportion of drug-resistant pathogens has risen rapidly, which has become the dominant race in Zhejiang and other places. At the same time, the distribution of drug-resistant pathogens has been expanding, which has spread from Zhejiang to most areas of Shanghai and Jiangsu. After a lapse of 20 years, the drug resistance of benzimidazole fungicides has attracted great attention from people in the industry. In some areas where the control effect of fungicides is declining, it is suggested to actively pay attention to new varieties, such as tebuconazole prochloraz mixture (Zamir) and cyazoxystrobin (Hu Jin). At the same time, attention should be paid to the correct mixing of drugs with different mechanisms of action, so as to ensure that the drugs used have multiple functions of internal inhalation treatment and protection and eradication, and completely prevent the spread of diseases. Four: less water consumption per mu is not conducive to the efficacy. According to the interview, some farmers in the wheat area use conventional sprayers, spraying water 15 liter per mu, and even less 10 liter. Such a small amount of water will affect the normal play of the drug effect. In order to ensure the efficacy, if a conventional sprayer is used, the water consumption per mu should be between 45 liters and 60 liters, or a efficacy assurance agent, such as a sprinkler, should be added. Fifth, we can't correctly grasp the frequency of drug use. There is no fixed standard for the frequency of medication. It is necessary to comprehensively consider factors such as bacterial quantity, incidence rate and drug control effect. It is necessary to treat the plots with serious diseases in previous years twice, and pay attention to spraying drugs after the rain. Remedial measures should be taken in time for the first ineffective drug. The second medication should be about 7 days after the first medication, which can better control the spread of bacteria and reduce losses. A comprehensive understanding of the characteristics of scab disease, grasping the incidence law, grasping the best prevention and control period, selecting appropriate prevention and control agents and applying them correctly can minimize the disease loss. (Author/Wang Guozhong)