An in-depth analysis of the comprehensive management strategy of citrus canker in Ningyuan County

An in-depth analysis of the comprehensive management strategy of citrus canker in Ningyuan County

Zeng Xiayu and so on

Ningyuan County is located in the south of Hunan Province, which belongs to the central subtropical monsoon humid climate zone, with abundant sunshine, abundant heat and abundant rainfall. The annual average temperature of Ningyuan County is 17.0 ~ 18.4 °C, the extreme minimum temperature is -2.9 °C, the annual effective accumulated temperature is 5 800 °C, the annual frost-free period is as long as 320 days, the annual average precipitation is 1 250.0 ~ 2 048.3 mm, and the annual average sunshine time is 1 644 h. In 2023, the planting area of citrus in Ningyuan County will be about 7 280.00 hm 2, an increase of 266.67 hm 2 over 2022. Canker disease may occur during the growth of citrus due to the influence of the environment, planting techniques, pests and diseases, etc. Citrus canker is a quarantine disease caused by bacteria, which spreads rapidly and is difficult to control. In recent years, the scale of citrus production in Ningyuan County has gradually expanded, and the incidence of citrus canker has increased year by year, and the difficulty of prevention and control has increased. In actual production, citrus varieties such as Maogu mandarin, Gong mandarin, mandarin orange, mandarin orange, mandarin orange, and Nanfeng mandarin may be infected with canker disease. The incidence of citrus varieties is also different, the incidence of susceptible varieties is higher; the incidence degree of citrus of the same variety is also different when the tree is different, and the disease of citrus with poor growth is more serious; the incidence of citrus will also be different in different environments, the closer to the source of the disease, the more serious the disease, the farther away and milder, or even not at all. Therefore, it is of great significance to analyze the comprehensive prevention and control technology of citrus canker disease and the corresponding prevention and control countermeasures.

1 Pathogenesis and epidemiological features

The causative bacteria of canker disease are gram-negative bacteria, which are harmed by the invasion of leaves, new shoots or stomata and wounds of young fruits under suitable temperature and humidity conditions, and the impact time lasts from the young fruit stage to the ripening stage of citrus. Through the investigation results of citrus canker in Ningyuan County, it can be seen that April to November is the occurrence period of citrus canker, and if it is not properly controlled, it may lead to the rapid development of canker. From May to August, Ningyuan County enters the rainy season, when the rainfall is abundant, the temperature is 20~35 °C, which is conducive to the reproduction and spread of canker pathogens. In addition, wounds caused by pests such as leaf miners and aphids also exacerbate the development of the disease. In addition to the lack of awareness of the disease, the random transportation and extensive management of diseased fruits, the mixed cultivation of multiple varieties in recent years is also an important reason for the epidemic of the disease.

2. Comprehensive prevention and control technology

2.1 Clean up diseased leaves, branches and fruits regularly

Before planting, the seedlings need to be inspected one by one, and the seedlings with mild disease should be dealt with in time, such as the leaf damaged seedlings should be removed in time, and the damaged seedlings of the branches should be cut off with a knife and cut to the xylem; 1 ~ 3 years after planting, the canopy of citrus trees is small and easy to observe, which can strengthen the prevention and control of canker disease during this time period. From the fourth year after planting, the citrus canopy grows to a certain size and the yield increases, making it difficult to see each plant and leaf by leaf. During this period, the prevention and control of pesticides should be the mainstay, and combined with the removal of diseased branches and leaves, in order to obtain good control effects.

2.2 Reasonable fattening

In order to improve the disease resistance of citrus trees, Ningyuan County should promote the development of citrus planting industry in the direction of standardization and standardization, adhere to the standard cultivation technology formulated by the state, industry, local and enterprise management, and reasonably increase the application of organic fertilizer and potassium fertilizer. During the growth and development period of young trees, top dressing can be carried out 8 ~ 10 times a year, and urea and compound fertilizer can be applied alternately. It can be fertilized by opening a ditch, with a length of 80 ~ 120 cm, a width of 20 cm and a depth of 10 cm. From November to December, 5 ~ 8 kg·hm -2 tung dry cake was applied, and the length of the fertilization furrow was 100 ~ 120 cm, the width was 30 cm, and the depth was 30 cm. After 4 years or 4 years, 3 ~ 4 times of compound fertilizer [m(N)∶ m(P2O5)∶m(K2O)=1.0 ∶ 0.3 ∶ 0.4] in the citrus growing season, 250 ~ 500 g· tree-1 ; After the fruit is harvested, 8 ~ 10 kg·tree-1 of tung dry cake is applied, the length of the fertilization furrow is 120 ~ 200 cm, the width is 30 cm, and the depth is 30 cm, and the soil and fertilizer are completely mixed evenly.

2.3 Chemical control

Chemical control is also an important pest control technology. Spray twice at the beginning of the citrus shoot when the new shoots are 3 ~ 5 cm long and the fruit is at the beginning of the disease, and spray again once in the young leaf stage if there is heavy precipitation or typhoon and other weather, and then spray once 10 d, 30 d, and 50 d after flowering. In the prevention and control once a year, spraying copper preparations once from June to August, the available agents are 53.8% can kill dry powder suspension 600 times, 20% copper pine acid micro emulsifiable concentrate 600 times, 77% dorining wettable powder 600 times, 50% royal copper wettable powder 600 times, and the rest of the time can be alternately applied 3% biocontrol biocontrol powder wettable powder 1 000 times and 2% chunleimycin water 1 000 times.

3. Prevention and control measures

With the change of consumption concept, people have put forward higher requirements for the quality of citrus. At present, the citrus industry in Ningyuan County has entered a period of rapid development, and the market competition is becoming increasingly fierce. In order to ensure the quality of citrus, citrus growers in Ningyuan County should uphold the plant protection concept of "prevention first, early prevention and control", and actively apply green and efficient comprehensive control technology to achieve pollution-free and high-quality production of citrus. Based on the characteristics and prevention and control technology requirements of citrus canker in Ningyuan County, the author puts forward prevention and control measures from the following three aspects.

3.1 Pay attention to the application of green and long-term governance technologies

1) Strengthen the training of fruit farmers, enhance their understanding and prevention and control ability of canker disease, so that they can develop from blind prevention and control to scientific prevention and control, independent prevention and control to group prevention and treatment, and single chemical control to green comprehensive control.

2) In the process of citrus planting management, the management system of citrus seedlings should be further improved, open planting should be eliminated, a disease-free seedling facility breeding system should be constructed, and fruit farmers should be guided to choose non-toxic (large) seedlings, so as to curb the spread of canker disease from the root cause and improve the economic income of fruit farmers.

3) Choose citrus varieties with good disease resistance. At present, there is no effective prevention and control method for citrus canker. Cultivating and selecting fruit trees with better disease resistance varieties for planting can reduce the probability of citrus canker infection. New citrus varieties with low tolerance, high yield and good quality should be selected to meet the needs of hilly and mountainous areas, and new disease-resistant citrus varieties should be cultivated to reduce the adverse effects caused by canker.

4) Reasonable clearing of the garden. Fruit growers need to properly clean their citrus orchards regularly during the planting process to effectively reduce the incidence of diseases. After the fruit is harvested, the fallen leaves, fallen fruits, dead branches, etc. are collected and burned in a centralized manner. In winter and spring, prune diseased branches, long branches, weak branches, etc., and prune the autumn shoots with overwintering larvae or pupae of leaf miners. Spray the plants and ground in the whole area with 48% chlorpyrifos EC 500 times, 80% Bordeaux 600 times, and 99% mineral oil 150 times, leaving no dead spots. It is necessary to put the work of clearing the garden in the first place in accordance with the principle of first clearing the garden and then putting new shoots, especially in spring and autumn before the new shoots are extracted, collect diseased branches and leaves and burn them in a centralized manner.

5) Optimize cultivation management. In order to reduce the adverse effects of citrus canker, citrus planting needs to be carried out in strict accordance with the standardized production technical specifications formulated by the state, industry and locality, specifically from the following three aspects. (1) Rational application of fertilizer. Increase the application of commercial organic fertilizer, dry cake fertilizer, farmhouse fertilizer and other fertilizers to enhance the vitality of citrus trees and enhance their resistance to stress. (2) Proper management of trees. Erase early autumn shoots and properly thin branches to promote the neat growth of new shoots and reduce the possibility of disease transmission. (3) Create a windbreak wall. Block the source of pathogens, reduce the damage of typhoons and heavy rain to citrus, and prevent the invasion of pathogens. (4) Application of fast-growing and high-yield cultivation technology. The rational application of cultivation technologies such as dense planting, grass cultivation, protection of natural enemies, planting large seedlings, and integration of water, fertilizer and medicine can effectively alleviate the harm of citrus canker.

6) Rational application of lime for disease control. After spraying high concentration lime water, the surface of citrus leaves is alkaline, which is not conducive to the growth of pathogens, and can have the effect of sterilization or bacteriostasis. Spray once within 20 days of fruit picking, use 1 part of quicklime and 3 parts of water to mix lime slurry, filter and apply, the trunk and branches should be sprayed evenly, this time it can also play a role in whitening and anti-freezing. In mid to late May, quicklime is filtered with water and sprayed evenly on branches and fruits, and can be sprayed again within 3 days if it rains.

7) Scientific treatment of ulcers. Timely and scientific treatment of canker disease is the key to the prevention and control of this disease. Fruit growers should frequently inspect the orchard during the citrus planting process, and if they find diseased fruit in the newly built (disease-free) orchard, they should collect and burn it as soon as possible. At the same time, the surrounding robust seedlings are applied and the large seedlings that have not developed the disease are rejuvenated to create a good citrus planting environment and reduce the infection of canker.

8) Pay attention to the promotion of insect net technology. Insect netting places citrus in a relatively independent space, which can effectively reduce the number of pests, and at the same time can reduce the impact of storms and strong winds on fruit trees, which can effectively reduce the occurrence of citrus canker and other diseases. Therefore, fruit farmers can apply insect nets to citrus when planting them, which can effectively control and reduce the incidence of diseases such as canker.

3.2 Precise application of enhanced agents

1) Insect control and disease control. Citrus leafminers can bring citrus canker bacteria to citrus, and control of citrus leafminers can stop the spread of canker. At present, 10~11 generations of citrus leaf miner moth occur in Hunan Province a year, with the peak period from June to September. In this regard, fruit farmers should focus on spraying and protecting shoots in summer and autumn, and comprehensively apply comprehensive treatment measures such as sex pheromone inducement and control, bud wiping and control, and timely spraying to protect shoots.

2) Pay attention to the critical period of pesticide application and control. Through the accurate grasp of the incidence of citrus canker disease and the phenological period of new shoots and young fruits in each season, timely application of pesticides can effectively reduce the harm of the disease. According to the climatic characteristics of Ningyuan County, the germination time of citrus spring, summer and autumn shoots was April 15-20, May 25-30, and August 10-15, respectively, so the prevention and control of fruit canker should be applied the first time on May 15-20, and then sprayed 1 ~ 2 times according to the specific situation in the next 10 days, and 6 ~ 9 times a year (1 ~ 2 times for spring shoots, 2 ~ 3 times for summer shoots, 2 ~ 3 times for autumn shoots, and 2 ~ 3 times for fruit protection). Medical protection should be used before or after typhoon rain.

3.3 Seize the critical period of prevention and control

In the seedling growth period, it is necessary to do a good job of protecting the shoots. After the germination of new shoots, it is necessary to do the first spraying treatment within 15 days, and then spray once every 10 ~ 15 days, a total of 3 times. In addition, the frequency of spraying should be increased for seedlings or young trees, and the main control goal of fruiting trees should be to protect young fruits, supplemented by treetop protection. When the sprout is 2 ~ 3 cm, spray for the first time to protect the new shoots, spray 1 time every 10 ~ 12 days, spray 3 times in a row, until the leaves turn green, and strive to spray 3 times per shoot. At 20 d, 35 d, and 50 d after flowering, spraying treatment was used to protect young fruits, which also played an important role in the protection of young shoots. 77% copper hydroxide wettable powder, 30% thiazole zinc suspension and other agents can be used, but in the process of medication, it is necessary to pay attention to the mixing and rotation of agents.

4 Conclusion

Citrus is the most important agricultural cash crop in Ningyuan County, and it is a regional characteristic agricultural product. The citrus industry in mainland China is in a period of vigorous development, but due to the change of ecological environment and the continuous rise of temperature, the occurrence scope of citrus canker disease has expanded and the degree of harm has deepened, so it is urgent to study it systematically. In the process of comprehensive prevention and control of citrus canker, attention should be paid to the application of green control technology, and the corresponding pesticide prevention and control work should be carried out based on the growth characteristics of citrus canker, so as to reduce the harm caused by canker, realize the effective prevention and control of citrus canker, and improve the economic benefits of fruit farmers.