Identification and control of pests and diseases

Identification and Prevention of Pests and Diseases On July 5th, 2002/KLOC-0, Maggie Cheung was fortunate to participate in the rural revitalization and pest control activities for agriculture, countryside and farmers initiated by the School of Biology and Food Engineering of Anyang Institute of Technology for the first time. After several days of investigation and visit, Maggie Cheung learned about the poverty alleviation strategy and the living conditions of residents in Ludian Town, Yichuan County, Luoyang City, Henan Province, which triggered her deep thinking and had many unprecedented insights. Figure 1. The event was officially launched. On July 5th, the Rural Revitalization Pest Control Team held a PPT demonstration under the organization of the person in charge, which made the team members have a certain understanding of the identification and control of pests and diseases. Figure 2. Identification and Prevention of Pests and Diseases On the afternoon of July 5th, after returning home, Maggie Cheung learned about the pests and diseases in his hometown and their prevention methods by surfing the Internet and consulting local villagers. The scientific name of Spodoptera exigua (Hü bner, 1808), also known as Spodoptera exigua, Spodoptera exigua, belongs to the family Lepidoptera. It is an omnivorous pest that harms corn, cotton, beet, sesame, peanut, tobacco, soybean, Chinese cabbage, tomato, cowpea, onion and so on 170 kinds of plants. Larvae is harmful to leaves. The newly hatched larvae feed on eggshells first and then climb out of the villi. 1-2 years old, often clustered on the back of leaves, feeding on mesophyll, leaving epidermis in the form of enough paper. Larvae after 3rd instar are scattered, which is harmful and can also eat bract leaves. They can eat leaves into nicks or holes, and start eating a lot after 4 years old. In severe cases, the mesophyll can be eaten up, leaving only leaves and petiole veins. Larvae above 3rd instar can also eat the ear, resulting in rotten ear [1]. Characteristics of damage and occurrence regularity of control methods Morphological characteristics: The adult body length is 10- 14 mm, the wing spread is 25-30 mm, the insect body and front wing are grayish brown, and the outer edge line of the front wing is composed of 1 row of black triangular spots, with kidney-shaped lines and yellow-brown ring patterns. Oval steamed bread-like, egg particles overlap, forming 1-3 layers of egg pieces covered with white fluff. Larvae's body color is changeable, generally green or dark green. The disc has yellow-white lower line, yellow-white longitudinal stripes on both sides, and sometimes pink. There are 1 obvious white stripes on the back and upper part of each disc. Four pairs of abdominal feet. The pupa is about 1 cm long and yellow-brown. Damage characteristics of Spodoptera exigua adults: the newly hatched larvae form a loose net and cluster on the back of leaves to feed on mesophyll. The damaged parts are reticular translucent window spots, which are longitudinally split after drying up. After the third instar, the larvae begin to cluster and damage, and the leaves can be eaten into holes and nicks. In severe cases, all the leaves are eaten up and the whole plant dies. After the fourth instar, the larvae began to eat a lot, such as leaves, petals, stems and pods [2]. The occurrence law occurs 5-6 generations a year and 7 generations a few years in the Yangtze River Basin. The farther south, the more years there are, and it can occur 10 ~ 1 1 generation in Guangdong in one year. Pupae mainly overwinter in soil, but there is no overwintering phenomenon in South China, which can endanger reproduction all year round. Adults have strong phototaxis and weak chemotaxis. They sleep during the day and come out at night. They hide in dark places such as leaf backs, grass and soil cracks during the day, and start to move in the evening, and they are most active at night. Eggs are mostly laid on the back of leaves, and there are more egg pieces on the lower leaves of seedlings than on the upper leaves. Tile one or more layers to overlap, and the egg pieces are covered with white scales. On some parts or weeds, the egg pieces are arranged in 1-3 layers and covered with white fluff. Each female can lay eggs 100 ~ 600. The egg period is 2-6 days. Larvae lie down during the day and come out at night, which is suspended animation. When it is slightly frightened, it rolls into a "C" shape and rolls to the ground. Larvae are afraid of strong light, and they often do harm in the morning and evening, and can do harm all day on cloudy days. When the population density is too high, larvae can kill each other. When mature larvae are buried, they will spin silk and build a room to pupate. The damage time of each generation of larvae in the Yangtze River Basin is:/kloc-0. The peak period of each generation is from May to late June, the peak period of the second generation is from mid-June to mid-July, the peak period of the third generation is from mid-July to late August, the peak period of the fourth generation is from early August to late September, the peak period of the fifth generation is from late August to mid-June and the peak period of the sixth generation is from late September to 65438+. Generally speaking, there will be overlapping generations from the third generation. The 3rd-5th generation in Shandong province is the heaviest, and the larvae occur frequently in Nanchang, Jiangxi province in June, with a peak from mid-September to 10. Larvae also occurred more frequently in Changsha, Hunan Province in June, and most frequently occurred from mid-September to1early October. Suitable temperature (or high temperature) and high humidity environmental conditions are beneficial to the growth and development of Spodoptera exigua. Generally, July-September is the peak period of damage, and July-August is characterized by low precipitation and high humidity, which is beneficial to its occurrence [1]. Prevention and control methods: agricultural prevention and control in pupal stage should be combined with agricultural needs, intertillage weeding, winter irrigation and deep ploughing. Weeds in the field should be eradicated in early spring, which will destroy the reproduction and habitat of early insect sources and worsen the feeding and spawning environment [2]. Physical control at night, artificial capture of older larvae and squeezing of egg pieces can effectively reduce population density. At the early stage of adults, black light, high-pressure mercury lamp and frequency vibration insecticidal lamp were set in the field to trap and kill adults, and sexual attractants were used to trap and kill adults [2]. Biological control uses Bt preparation, using natural enemies such as Hemiptera, CERATOPOGONIDAE, leopard spider, CERATOPOGONIDAE, etc. The dominant natural enemies of eggs are black egg bee, Trichogramma brevis, etc. The dominant natural enemy of larvae is Metarhizium anisopliae [2]. The best time for chemical control should be early morning. Before 8 am or after 6 pm, spray 1000-2000 times of 25% chlorfenuron EC, 1000 times of beta-cypermethrin EC and 500 times of 5% flufenoxuron EC or 1000 times of 5% beta-cypermethrin EC. Figure 3. Spodoptera exigua maize leaf blight is a disease caused by Helminthosporium tumefaciens, which occurs in maize. It mainly harms leaves, and even leaf sheaths and bracts in severe cases. Generally, it gradually expands from the bottom leaves, which can spread throughout the whole plant in severe cases, but there are also cases of middle and upper leaves. [1] The northern leaf blight of maize is one of the important diseases of maize, which is widely distributed in maize cultivation areas all over the world. Generally, the production will be reduced by 15-20% in major years, and by more than 50% in severe years. The occurrence and prevalence of the disease are affected by many factors, such as the disease resistance of inbred lines, crop rotation system, climatic conditions and cultivation measures. With the popularization of disease-resistant varieties and the change of cultivation system, the harm of diseases was once controlled, but further research and control are still needed. [1][2] The epidemic of maize northern leaf blight is determined by three factors: one is the large-scale planting of susceptible varieties, the other is the existence of a large number of pathogenic bacteria, and the third is the availability of suitable environmental conditions. Therefore, the control of maize leaf blight should start from these three aspects. [1] The epidemic regularity and control methods of the symptom infection cycle of maize leaf blight. The pathogen of maize leaf blight is Helminthosporium tumefaciens, which belongs to Hemiptera, Myxomycetes and Helminthosporium. Conidia develop from stomata, which are brownish green, solitary or 2-6 clusters, unbranched, upright or bent into knees at the upper part, with 2-6 (mostly 3-5) septa, with the size of (12.5-188.7) μ m×10. Conidia 1 to several terminal ones, colorless at first, then turned brown-green, spindle-shaped, straight or bent to one side, and most of them had 4-7 septa with the size of (57.7-140.6) μ m× (15.1-20. Heterothallism body is black, oval or nearly spherical, with a height of 359-72 1 micron and a width of 345-497 microns. Ascomycetes are cylindrical or rod-shaped, with short stalks, and the size is (176-249) μ m× (24-31) μ m. Generally, there are 2-4 ascospores and 1-6 ascospores. Mature ascospores are colorless, spindle-shaped, straight or curved, with three septa and constricted septa, and the size is (42-78) μ m× (13- 17) μ m. [3] 1 conidia and demodex folliculorum show the following characteristics. There are corn specialization, sorghum specialization, John grass specialization, bonzi specialization and so on. The specialized types of maize are divided into race 1 and race 2, and race 1 is distributed in China. [3] The symptoms of maize northern leaf blight mainly damage leaves, but also damage leaf sheaths and bracts in severe cases. Mr. Ye in the lower part of the plant got sick and then spread upward. The lesion was spindle-shaped, taupe or yellowish brown, with a length of 5- 10 cm and a width of about 1 cm. Some lesions are large, or several lesions are connected together to form large irregular withered spots, and in severe cases, the leaves are scorched. Water stains first appeared on susceptible varieties, and quickly developed into gray-green spots. The lesion spreads rapidly along the vein, and is not limited by the vein, forming a large area of lesion with a long spindle shape, gray-brown center and no typical discoloration area at the edge. On rainy days, a gray-black mold layer will appear on the plaque, which is mainly caused by a large number of pathogenic spores. After the disease, the leaves of the plant lose their photosynthetic function, which makes it difficult to ensure the normal growth of the plant. In severe cases, plants will die, resulting in large-scale production reduction. Occurred in disease-resistant varieties, the disease spots spread along the veins, showing brown necrotic stripes, surrounded by yellow or light brown chlorosis rings, and no or less spores were produced. [4][5]*** 13. The pathogen of corn leaf blight infecting circular corn leaf blight overwinters in the disease body with its dormant mycelium or conidia, which becomes the primary infection source of the following year. During the growing season of maize, spores produced by overwintering bacteria spread to maize leaves with rain splashing or airflow, and germinate and invade under suitable temperature and humidity conditions; After 10- 14 days, a large number of conidia can be produced. After that, conidia spread with wind and rain and repeatedly infected. [5] Soil fertility has certain influence on the occurrence of maize leaf blight. Some fields with low soil fertility will lead to poor growth and development of corn, reduced disease resistance and prone to corn leaf blight. In the production process, soil testing and fertilization are needed to supplement nitrogen and potassium to improve soil fertility, which can increase plant growth, improve disease resistance and reduce the degree of disease to a certain extent. [4] Climatic conditions In the process of corn growth, if the temperature is low, the climate is cool and rainy, and the humidity is high, it is easy to cause corn leaf blight, because such climatic conditions are conducive to the spore separation of the pathogen of leaf blight and the spread of the disease. [4] Different varieties have different resistance to Great Leaf Blight. In actual growth, varieties with strong resistance should be used as much as possible, and varieties without resistance should not be used blindly in pursuit of yield, because susceptible inbred lines and susceptible varieties will lead to the epidemic of Great Leaf Blight in the whole field, and once it breaks out in a large area, its losses will be incalculable. [4] Tillage system Because the pathogen of northern leaf blight of maize will remain on the diseased plants in the form of hyphae and spores, it can get sick the next winter. Many farmers only harvest the ears of corn, some plants are abandoned in the field, some stalks are harvested, but some corn stubble and diseased leaves will still remain in the field, so a large number of diseased leaves will become the source of infection of Great Leaf Blight. In addition, there are many areas where corn is planted continuously, which also provides conditions for the occurrence of corn leaf blight. The continuous cropping corn field has poor ventilation and light transmission, and the field humidity is high in rainy season, which provides climatic conditions for spore meristem. 【 4 】 Prediction system of prevention and control methods In areas with frequent occurrence of northern leaf blight of maize, designated persons are responsible for regularly and systematically observing the occurrence and growth and decline of northern leaf blight of maize. When diseased plants appear in the field and diseased leaves start to spread vertically from bottom to top, such as high humidity in the field or moderate to heavy rain in the recent weather forecast, the forecast that "Great Leaf Blight of Maize will be prevalent in about 10% of the field" should be released quickly to guide farmers to prevent and control it in time. [2] The climatic conditions of agricultural control are the decisive factors affecting the occurrence of Great Leaf Blight. Moderate temperature and high humidity are the main climatic conditions of rust leaf blight, such as annual average temperature, rainy days and high atmospheric humidity in the field, which cause sudden disasters of corn leaf blight. 20-25℃ and relative humidity above 90% are beneficial to the development of the disease. Therefore, it is necessary to choose a place with suitable humidity and temperature to plant corn, so as to fundamentally control the northern leaf blight of corn. [6] Actively promote disease-resistant varieties. The decline of disease resistance of varieties is one of the important factors leading to the occurrence and epidemic of diseases. It is generally not easy to plant disease-resistant varieties under the condition that a large number of pathogens are accumulated in the field. The resistance of different maize varieties to Great Leaf Blight is very different, and planting excellent resistant varieties is the main measure to control Great Leaf Blight. In areas with frequent occurrence of Great Leaf Blight, disease resistance should be the first consideration in the selection of maize seeds, and attention should be paid to the reasonable collocation and rotation of varieties to avoid variety simplification. [6] Improve the culture environment. Implement crop rotation and stubble rotation in a planned way, avoid continuous cropping and plant in advance. In the form of planting, it is necessary to change equal spacing sowing into wide and narrow row planting, and change large area flat sowing into intercropping of high and short crops, improve the ventilation and light transmission conditions in the field, and promote the robust growth of corn. After corn harvest, no matter in Pingchuan or hilly and mountainous areas, efforts should be made to prevent the white stubble from overwintering, apply sufficient fertilizer, optimize formula fertilization, popularize plastic film mulching, and sow early in time, which can make the most dangerous susceptible period of corn avoid the high temperature rainy season, thus greatly reducing the harm of corn leaf blight and creating a good ecological environment for improving plant disease resistance. [6] Chemical control According to the condition, the yellow leaves and diseased leaves at the base of the plant should be removed first to reduce the source of reinfection and enhance the transparency of ventilation before spraying fungicides. Spraying control at the end of heart leaves to tasseling stage or early onset stage. Every day 10 day, 1 time, 2-3 times in a row. The medicament is 50% Haosujing wettable powder 1000 times, 80% Sukejing wettable powder 1000 times, 500 times of carbendazim wettable powder, 600 times of thiophanate-methyl wettable powder, 300 times of chlorothalonil wettable powder or 8000 times of benomyl 25% emulsifiable concentrate. You can also use 80% mancozeb wettable powder 50g/ha, or 70% thiophanate-methyl wettable powder 1.5kg/ha, or 50% carbendazim wettable powder 1.5kg/ha, or 75% chlorothalonil wettable powder 1.5kg/ha. Figure 4. Based on the local villagers' conversation and information search, Maggie Cheung learned about the morphological control methods of Spodoptera exigua and his understanding of corn leaf blight. ? At the end of the activity, Maggie Cheung's greatest feeling was that it was very important to identify and control pests and diseases. In the process of agricultural production, pests and diseases pose a great threat to agriculture, so how to control plant pests and diseases is the focus of current research. Nowadays, many people know little about the harm of pests and diseases, and even don't know how to solve this problem. Therefore, in this case, it is necessary to publicize the harm of plant diseases and insect pests and how to deal with them. So on July 10, Maggie Cheung made a publicity and explanation in the village, telling what she had learned before.