Resistance to vegetable diseases and insect pests and its control measures
Changchun Zhang (Institute of Ecological Environment, Wenzhou Academy of Sciences)
Liu Huazhou (Wenzhou National Agricultural Production Information Company)
The problem of drug resistance is a prominent issue in current vegetable production. The long-term single dependence on chemical control and unreasonable use of pesticides have exacerbated the formation and development of insecticide resistance in vegetables. This has not only brought great difficulties to the management of pests and diseases, but also aggravated the pollution of pesticides to the environment. Therefore, effective measures must be taken to control them. And prevent and delay the development of drug resistance. The following is a summary of the development of the basic essentials of vegetable pest resistance and its treatment strategies.
1 Resistance to insects and fleas
1.1 Drug resistance and its formation
In general, any pest or cockroach that has the ability to endure a certain pesticide significantly kills the doses of most individuals in its normal population and develops into a strain (match) can be said to be such a pest or cockroach. It has developed resistance to this type of pesticide. For agricultural pests and cockroaches, it is usually used as a lethal medium or lethal concentration of a pesticide or a suspected strain of cockroach to kill a pesticide. When the amount or concentration exceeds the third line by more than two times, the pests and cockroaches are considered to have drug resistance, and the greater the degree of multiplication, the higher the degree of resistance.
The formation of drug resistance is generally believed to be the prevention and control of certain pests and acarid populations in a certain area due to the long-term continuous use of the same pesticide, and the original resistance genes in the population according to the law of survival of the fittest. The individual survived. Under the influence of the selective pressure of pesticides, the induction of resistance by the pesticides is strengthened and the reproduction of the generations is expanded, gradually forming a resistant strain with markedly decreased control efficiency. Therefore, the resistance of pests and cockroaches refers to the characteristics of the population, not the result of individual changes, and drug resistance is heritable.
1.2 Classification of drug resistance
1.2.1 Single resistance refers to a kind of pests and cockroaches that only produce resistance to certain pesticides.
1.2.2 Cross-resistance. Refers to a pest, cricket that has developed resistance to an agent and is also resistant to certain agents that have not been used. For example, orange spider mites resistant to dimethoate are also resistant to eight organophosphorus pesticides such as marathon and trichlorfon. In terms of aviation, all agents with similar or similar mechanisms of action are more likely to produce cross-resistance. On the contrary, it is not easy to produce, but it is not absolute. For example, it has been reported that the population of brown rice borers against marathon or leafhoppers showed resistance 70-120 times that of permethrin.
1.2.3 Joint resistance. A single pest-resistant pest or aphid strain, due to the selective effect of another agent, not only maintains resistance to the former agent but also develops new resistance.
1.2.4 Negative cross-resistance. Pests and cockroaches that are resistant to an agent are more sensitive to another agent and are more likely to be killed. For example, Japan reported that the resistance to application of fast pyrethroids against marathon's rice leafhopper was 4.3 times higher than that of normal sensitive populations.
It should be noted that the resistance to pests and cockroaches must be carefully identified. To pass the test, the difference in control effect caused by environmental changes, different insect ages, different medication seasons, different time, the number of drugs used, and the quality of the pharmaceutical agents should be differentiated from the drug resistance.
1.3 Causes of Drug Resistance
1.3.1 In vivo detoxification enzyme enhancement. The multifunctional oxidases in pests and ticks can detoxify, hydroxylate, and oxidize the organophosphorus, organochlorines, carbamates, and pyrethroids and lose their toxicity. Some of these agents can also induce the enzyme. , increase its quantity and activity, thereby enhancing detoxification and drug resistance. In addition, amidase, glutathione transferase, dehydrochlorinase, carboxylesterase, phosphatase, etc., can also render some of the agents resistant to loss of toxicity.
1.3.2 Reduce the third degree of poisoning. For example, organophosphorus and carbamoyl esters are cholinesterols for poisoning of pests, while cholinesterases of resistant pests and cockroaches are less sensitive to poisoning.
1.3.3 Penetration of the medicament is reduced. The penetrants of pests, cockroaches and the protective sheath of the cockroach are changed in the permeability of the medicament, so that the medicament enters slowly or cannot reach the affected portion, resulting in the medicament being degraded in time to reduce the virulence or lose the virulence.
2 Resistance to pathogens
About nine-tenths of the resistance of pathogenic bacteria to fungicides occurs within the systemic fungicide, especially selective fungicides with strong specialization. The most common are benzoimidazole fungicides, followed by antibiotics.
The reason for the emergence of resistant strains: It is generally believed that the presence of resistant strains in the field is due to the selective pressure of the pesticides, which changes the proportion of sensitive strains and resistant strains. After a few generations of resistant strains predominated, the efficacy of their final performance was significantly reduced.
The main physiological and biochemical mechanisms of resistance are as follows: 1. The permeability of the bacteria to the drug is reduced. 2, enhance the ability of bacteria to detoxify and promote the decomposition of drugs. 3, reduce the affinity of the drug and bacterial sites. 4, rapid synthesis of poisoning enzyme (sensitive enzyme).
3 Status of Vegetable Pest Resistance
3.1 More prominent pests and diseases at home and abroad
At present, the most prominent pests and diseases of vegetables at home and abroad are: Plutella xylostella, Beet armyworm, Pieris rapae, Spodoptera litura, Brassica juncea, Bollworm, Bemisia tabaci, and greenhouse whitefly.
3.1.1 Plutella xylostella. According to reports, the insect has developed resistance in the Philippines, Japan, Malaysia, Taiwan and the United States. In China, in Shanghai, Guangzhou, Shenzhen, Wuhan, Kunming and Guizhou, diamondback moth has produced dozens of times more pesticides than organic pesticides, carbamates, organochlorines, pyrethroids, and Bacillus thuringiensis. Even thousand times more resistant. For example, in the Yangtze River Basin in 1995, the resistance index to fenvalerate and imidophos in the diamondback moth of the Yangtze River reached 1646.79 and 512.15 times, respectively. In the past, it was generally considered that insecticide resistant insect growth regulators were not readily available; in some areas, diamondback moth was abamectin. The sensitivity has decreased and even reached the level of mid-resistance. There are data that the resistance of the diamondback moth to avermectin is as high as 812.7 times after 27 generations.
3.1.2 Spodoptera litura. According to reports, this has long produced resistance to organochlorines, organophosphorus, pyrethroids, carbamates, and Bt pesticides. According to measurements in Shanghai, the resistance of Spodoptera litura to cypermethrin, deltamethrin, and fenvalerate was 43.9, 90.0, and 171.9 times; the resistance to dichlorvos and acephate was 29.7 and 33.6 times, respectively.
3.1.3 Spodoptera exigua. The use of cypermethrin, fenvalerate, and other pyrethroid pesticides in the Yangtze River Valley in 1986 was still 70%-86%, but it was virtually ineffective from 1993 to 1994; organophosphorus pesticides and methomyl (carbamic acid) Efficacy of conventional amounts of esters also declined rapidly around 1986; it was reported that the resistance to fenvalerate, deltamethrin, and acephate reached 238, 225.2, and 53.9 times, respectively, in 1994.
3.1.4 Other pests. According to reports, the whitefly in the greenhouse of Beijing Sijiqing. In 1998, the resistance to deltamethrin and fenvalerate malathion was increased by 6289.1, 1941.7, and 66.2 times, respectively, compared with 1983; in 1990, the green leaves of Beijing area were resistant to deltamethrin and fenvalerate. At about 100 times, the resistance of P. rapae in Shanghai to acetamiphos, trichlorfon, and fenvalerin enzymes was 8.5, 378, and 50 times, respectively; from 1991 to 1992 in Beijing, Peach pods were found in Dimethoate and Mara The resistances of parathion, quinoxa, fenthion, chlorpyrifos, deltamethrin, anti-indolin, and methomyl were 230, 32, 19, 123, 39, 114, 245, and 39 times, respectively; The new insecticides that have just begun to be applied in China, such as hi, chuchu, ray opera, Miman, and Anda, have been shown to have increased resistance to harmful insects in some areas and reflect a significant drop in efficacy.
3.2 Status of Resistance to Vegetable Pests and Diseases in Our City
The disease resistance of vegetable pests and diseases in our city developed rapidly, and the level of drug resistance was generally higher. The main reasons were the high multiple cropping index, multiple types of diseases and insect pests, high frequency of occurrence, large and frequent chemical control, and long-term single dependency on chemistry in production. Prevention and control, blindly increasing the concentration of the drug and increasing the frequency of drug use were common and serious. As a result, the frequency of medication and the amount of medication per unit area of ​​the vegetable field increased continuously and remained high. In many places, many of the original pesticides with good efficacy have been found for several years, and as a few months, the total efficacy has dropped significantly or is virtually ineffective. In addition, some newly-developed pesticides are first used in vegetables with good economic benefits because of high costs. Some diseases and insect pests have increased resistance to several new pesticides, and their efficacy has dropped significantly.
According to the author's experiments and investigations, the pests and diseases that are currently resistant to or exhibit resistance to one or more pesticides in vegetable production in the city mainly include: Plutella xylostella, Spodoptera litura, Spodoptera litura, and yellow song stripe. Bemisia tabaci, powdery mildew, downy mildew, and gray mold. Among them, the common pests of Plutella xylostella, Spodoptera litura, Spodoptera littoralis, Brassica juncea, Bemisia tabaci, and Thrips falciparum have been widely used to produce different levels of resistance to organophosphorus, pyrethroid, and carbamate pesticides. In some areas, Plutella xylostella has different degrees of resistance to avermectin and teriprofen, and low or moderate resistance to antibiotics and Bt pesticides. According to Wenzhou City Agricultural Science, the resistance index to abamectin was 6.28-22.15 times, and it was 6.80-41.81 times higher than that of the Chinese Academy of Agricultural Sciences. The conventional dose of Sitabao in the local area was found in the larvae of Spodoptera exigua and Spodoptera litura. The control effect is only 30%-40%, and the control effect of chlorfenadyl on the whitefly is only 20%-30% or even completely ineffective; The control effect of conventional doses on N. lugens decreased, and the conventional dose of fenvalerate had only 40% to 50% of the control effect against the yellow fleas; some local cinereas were resistant to fast keratin, chlorothalonil, and ten thousand. Three kinds of farmers, such as mold and spirit, have developed resistance to varying degrees, among which the resistance to pentetracycline is the most serious, followed by sucrokine and chlorothalonil; in the majority of areas, powdery mildew resistance to triadimefon shows resistance. The effect is only 20-40%; in some areas, the conventional doses of metalaxyl, chlorothalonil, and anti-mite have only 20%-50% efficacy against downy mildew.
4 Control measures against drug resistance
4.1 Main Measures for Preventing and Delaying the Production of Resistance to Pests and Earthworms
4.1.1 Make full use of various effective non-pesticide control measures. In the prevention and control of pests and cockroaches, priority should be given to adopting agricultural control techniques as much as possible, and active application of physical and biological control technologies should be used. Modest use of pesticides should be used only when necessary to minimize the frequency and dosage of medicines. Specific methods are: 1, as far as possible the use of high-quality, insect-resistant or insect-resistant varieties. 2. The rational distribution of crops and intercropping will worsen the nutrient and living conditions of pests and earthworms, destroy their normal life history, and suppress the occurrence of pests and cockroaches. 3, deep plowing farmland, summer exposure, winter irrigation, etc., destroy the living environment of underground pests. 4, rational close planting, timely cultivator, clean garden, scientific management of fertilizer, improve the crop's resistance to insects, cricket capacity and tolerance. 5. Use pest tropism, use light, color, taste, sex pheromone and attracting crops to monitor and trap pests. 6. Use artificial killing such as group moths of insect pests and high insect-egg masses. 7, to create conditions conducive to the survival and reproduction of natural enemies, to promote the development of natural enemies population, and enhance natural enemies against the natural inhibition of pests and cockroaches.
4.1.2 Alternating pesticides with different mechanisms of action. The alternative use of pesticides with different mechanisms of action is a crucial measure for preventing or delaying the development and development of pest resistance and resistance to insecticides. In general, the number of times that the same pesticide is applied to each vegetable should not exceed two times. Generally speaking, a pesticide can be used properly, can maintain an effective service life of about 15-20 years, and use an improper lifespan for only a few years, and the expiration time is shorter. For pests and cockroaches that have developed resistance to insecticides, effective pesticides with different mechanisms of action should be used for prevention and control. In principle, insecticides and pesticides that have produced drug resistance should be suspended.
4.1.3 Mix pesticides scientifically and rationally. Scientifically and rationally mixing, especially the scientific and rational use of pesticides with different mechanisms of action, can not only prevent or postpone the development of resistance, but also have both concurrent and synergistic effects. Some people used a marathon to deal with SBPH. After 13 consecutive generations of treatment, the median lethal dose increased by 110 times. However, with a marathon plus (1:1) mixture, the median lethal dose only increased after 15 consecutive generations of treatment. 2 times. However, pesticides used for temporary mixing should not be more than two in general, so as to reduce the occurrence of poisoning or reducing efficiency and wasting of pesticides.
4.1.4 Scientifically treat every medication. When implementing each pesticide control, it is necessary to choose the appropriate pharmaceutical or formula, strengthen the measurement and reporting, strictly control the appropriate period of control, control indicators and application of low-use concentration and other drug technologies. Blind use of drugs can easily accelerate the development and development of drug resistance.
4.1.5 Try to use eco-selective pesticides. In the implementation of chemical defense, the use of ecologically-selective pesticides that have a large number of pests and cockroaches and have a low impact on natural enemies should be used as far as possible to reduce the proportion of pests and natural enemies to a low balance.
4.1.6 Use of agents with negative cross-resistance
4.1.7 Add synergist. The synergist itself is non-toxic, but it can be used to counter the activity of detoxifying enzymes in the helminths. Therefore, combined with pesticides can improve the toxicity, such as the oxidation of pepper-based aldoximine, sesamin, piperine, safrole, etc. added in the carbaryl, the prevention and treatment of cotton aphids significant efficiency.
4.2 Main measures to prevent and delay the development of resistance to pathogens
Taking full advantage of various effective non-pesticide control and prevention techniques, minimizing the number of pathogenic bacteria and reducing the amount of pesticides applied, it is currently believed that fungicides with different mechanisms of rotation or alternate use are more effective.
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