What are the methods for pollution-free tea pest and disease control
How to control pests and diseases in pollution-free tea? Please guide. The development of integrated pest management technology has ensured high-quality and high-yield tea production, but there are still some problems that urgently need to be solved, especially the development of pollution-free tea production, which has put forward higher requirements for pest and disease control. Tea garden pest and disease flora changes...
How to control pests and diseases in pollution-free tea? Please guide
The development of integrated pest management technology has ensured high-quality and high-yield tea production, but there are still some problems that urgently need to be solved, especially the development of pollution-free tea production, which has put forward higher requirements for pest and disease control
Changes in tea garden pest and disease flora and their causes
1 Characteristics of pest and disease flora changes Over the past half century, the changing trends of tea plant pests and diseases in China have shown the following characteristics:
1) Succession from large-bodied pests toward small-bodied pests such as aphids, mites, scale insects, thrips, and leafhoppers;
2) Succession from chewing-mouthpart pests toward sap-sucking pests;
3) Succession from pests with few generations and low reproductive rates toward pests with many generations and high reproductive rates;
4) Succession from pests that cluster on leaf surfaces and are easily exposed to pesticides toward pests with hidden habitats such as leaf-rolling, leaf-mining, or protected by waxy shells or scale covers, which are not easily exposed to pesticides.
The changes in tea plant disease types are not as obvious as those of tea plant pests.
2 Analysis of the causes of flora succession
1) Adaptability to the ecological environment. Each organism has a certain stability in its long-term adaptation to its surrounding environment, but also has a certain degree of plasticity, so it can settle and reproduce in new areas. For example, due to the obvious synchronization between the peak hatching period of the 1st-2nd generation eggs of the tea geometrid and the unfolding period of tea buds, and its many generations per year, this pest, in addition to being an important pest in the history of Zhejiang Province, has now spread to Jiangsu, Anhui, Hunan and other provinces, with its occurrence range gradually expanding, which is related to the strong adaptability of this pest to the ecological environment.
2) Changes in cultivation techniques and measures. Changes in cultivation measures alter the habitat environment of the pest and disease flora, thus leading to changes in the pest and disease flora. For example, the development of tea gardens toward semi-mountainous and mountainous areas has allowed populations such as the small green leafhopper and tea white star disease to develop. The heavy use of nitrogen fertilizer has changed the amino acid composition in tea buds and leaves, causing the occurrence numbers of tea scale insects, mites, and tea leaf diseases to rise somewhat. The promotion of the leaf-retaining picking technique in the 1960s provided egg-laying sites for the tea leaf roller, causing this pest to occur in large numbers nationwide from the mid-1970s. The development of famous and high-quality tea in the 1990s required higher tenderness in picking, thus leaving the tender shoot stems bearing large numbers of small green leafhopper eggs on the trees, thereby intensifying the occurrence of leafhoppers.
3) Irrational use of chemical pesticides. The non-selective toxic effect of chemical pesticides means that when pesticides are used, they not only kill pests but also kill natural enemy insects, thus leading to rampant outbreaks of certain pests. For example, the rampant outbreak of scale insects in Chinese tea gardens in the mid-1960s was related to the heavy use of organochlorine pesticides (BHC and DDT) starting in the 1950s. Similarly, the widespread use of organophosphate pesticides from the early 1960s reduced the population numbers of scale insects sensitive to organophosphate pesticides, but because they have strong killing power against mite natural enemies and weak killing power against pest mites, especially very low activity against mite eggs, this in turn caused rampant outbreaks of tea pest mites nationwide from the late 1960s. These were 2 obvious population successions in China since the 1950s.
Current problems in tea plant pest and disease control
Judging from the current requirements for tea plant pest and disease control under the new situation, there are problems in the following aspects:
1 Several major tea plant pest and disease species still lack new effective control technologies. Although effective control technologies already exist for the major pest and disease species in tea gardens, enabling pest and disease populations to be basically controlled, as China is on the eve of joining the WTO, many developed countries have successively formulated new maximum residue limit (MRL, hereinafter referred to as) standards for pesticides in tea, which has restricted some technologies used for many years. For example, the currently most important pest species in tea production, the small green leafhopper, has long relied mainly on chemical control, and the long-used dimethoate has become increasingly less effective in many areas, while foreign MRLs for it also show a trend of gradual tightening. Fenvalerate is an important pesticide used in tea gardens to control the small green leafhopper since the 1980s, and since November 1999 it has been banned from use in tea production by order of the Ministry of Agriculture. The promotion of famous and high-quality tea has made picking standards increasingly tender, thus leaving more tender shoot stems on the trees; compared with the older picking standards of the past, which could pick off large numbers of leafhopper eggs, this actually weakens the strength of agricultural control of the small green leafhopper. The black citrus whitefly is a pest that has risen to a dominant position in many tea gardens since the 1990s; the long-promoted and applied buprofezin (Yoled, Pufuiling), because the new EU standard sets its MRL at 0.02 mg/kg, can only stop being used in tea gardens, even though it is very effective against the black citrus whitefly, and currently there is no pesticide that can completely replace it. The tea black tussock moth occurred only sporadically in local areas before the 1980s and generally caused little damage, but since the late 1990s its occurrence area has become larger and larger, and effective control measures are still lacking.
Besides tea plant pests, the control of tea bud and leaf diseases has long used chemical control methods. Because the MRL standards for commonly used fungicides are set very strictly, integrated control measures for tea bud and leaf diseases that reduce the amount of chemical pesticides need to be proposed as soon as possible.
2 The rate of pesticide MRL exceedance in tea is very high, affecting tea exports. The residue problems of the two pesticides DDT and BHC in Chinese tea were once serious problems affecting tea exports in the 1960s-1970s. With the attention of governments at all levels, safe and rational pesticide use and integrated pest management measures were implemented, so from the mid-1980s the pesticide residue problem in tea was fundamentally solved, with more than 98% of China's exported tea and more than 95% of domestically sold tea meeting international and domestic permitted standards, respectively. However, on the eve of China's joining the WTO, some developed countries, especially EU countries, successively expanded the scope of pesticide MRL testing in tea, from only 6 pesticides in the past to nearly 100 pesticides, while also greatly lowering MRL values. For example, the MRL of fenvalerate in tea implemented by the EU before July 1, 2000 was 10 mg/kg, but after July 1, 2000 it was changed to 0.1 mg/kg, and for many pesticides the minimum detection limit standard of 0.02 mg/kg was implemented. Thus in 2000 this caused a relatively high rate of pesticide residue exceedance in tea. It must be explained that this exceedance rate was calculated according to the EU's new standards; if calculated according to the standards promulgated by China, then the vast majority of tea still met the standards. From the test results, the highest exceedance rates were for 3 pesticides: fenvalerate, fenpropathrin, and Yoled. This exceedance phenomenon is clearly improving under the attention of governments at all levels.
3 Lack of technologies and pesticides suitable for pollution-free production use
With social progress and scientific and technological development, people have higher requirements for food safety. The production of pollution-free tea has become a government action in the new century and will become a market access standard in just a few years. At present, pollution-free tea production has become a hot topic in all tea-producing provinces across the country. However, many technical problems in pollution-free tea production remain unsolved, and it is urgent to solve how to use less or no pesticides in pest and disease control. It can be expected that biological control methods will be used more, adopting biological pesticides and botanical pesticides. But so far, these technologies and products, whether in quantity or quality, are far from meeting the needs of pollution-free tea production, and to date no biological pesticide formulation that can be mainly used for tea plant pest and disease control has been registered and approved.
Integrated control of tea plant pests and diseases in the new century
The Ministry of Agriculture proposed in 2000 that pollution-free products will be the goal and requirement of tea production, and also the market access standard for future tea products. Therefore, tea pest and disease control should also take this as the goal and propose ideas for integrated control. It should be considered from the overall balance of the tea garden ecosystem, not limited only to the control target; it is necessary to consider not only the pest and disease species at the time and place, but also the future and environmental protection; it is necessary to consider not only current interests and benefits, but even more the long-term impact and consequences. In terms of measures, it should be considered to use no or less chemical pesticides, and agricultural control and biological control should be strengthened. The following aspects should be especially strengthened.
1 Improve the tea garden environment and give play to the tea garden's natural regulatory capacity
The tea garden is the habitat for tea plant pest and beneficial organism populations. Maintaining a good ecological balance in the tea garden environment and paying attention to the ecological environment around the tea garden, in order to maintain and improve the dense canopy closure of the tea garden and the tree planting around the tea garden, can help the biodiversity of the tea garden ecosystem and give play to the tea garden's natural regulatory capacity, so as to achieve a balance of biological populations in the tea garden ecosystem. This is an indispensable external ecological condition for implementing good integrated control.
2 Take agricultural control as the foundation and strengthen ecological regulation Based on field cultivation management, agricultural control takes changing the habitat environment of the tea garden ecosystem as its main goal and is a mild regulatory measure, so in pollution-free tea production the control of harmful organisms will play an increasingly important role.
When developing new tea gardens, attention should be paid to selecting and matching different clonal varieties, and attention should be paid to selecting clonal varieties with higher resistance to local major pests and diseases. Picking can reduce the occurrence of the small green leafhopper, tea aphids, and tea mites. Fertilization is closely related to pest and disease occurrence. In Japan, ultra-high nitrogen fertilizer application over the past 20 years has caused tea anthracnose to become epidemic and root rot to occur severely. In addition, partial application of nitrogen fertilizer changes the amino acid composition in tea buds and leaves, increasing the proportion of acidic amino acids, which favors the occurrence of piercing-sucking mouthpart pests (such as scale insects and mites). The application of organic fertilizer can increase the content of neutral and basic amino acids, which is unfavorable to the occurrence of aphids, scale insects, and mites. It can thus be seen that using agricultural technical measures to improve ecosystem function, thereby controlling pest and disease occurrence, achieves twice the result with half the effort.
3 Strengthen biological control and protect and utilize natural enemy resources. Beneficial organisms are another trophic level in the tea garden ecosystem besides tea plants and harmful organisms. They have the characteristics of strong specificity and no environmental pollution, and are also a powerful means of ecological regulation of tea plant pests. In the production process of pollution-free tea, strengthening biological control and reducing the amount of chemical pesticides is of great significance. Biological control includes beneficial microorganisms, viruses, parasitic natural enemies, and predatory natural enemies. Among beneficial microorganisms, more than 20 kinds have been successful in tea plant pest and disease control, including Bacillus thuringiensis, Beauveria bassiana, aphid mold, Aegerita webberi, Aschersonia, etc. Aegerita webberi, isolated from the black citrus whitefly in the 1990s and successfully reproduced and applied, was the first Aegerita fungus used in pest control at home and abroad; after large-scale application in Fujian and Zhejiang, its field control efficacy was above 70%, with a persistence of at least 3 years. The application of insect viruses has achieved great success in the control of tea plant pests. China has isolated 63 insect viruses from more than 40 kinds of tea plant pests, including 38 nuclear polyhedrosis viruses, 17 granulosis viruses, 5 cytoplasmic polyhedrosis viruses, and 3 non-occluded viruses. Tea geometrid NPV virus and tea tussock moth NPV virus have reached the level of large-scale application in China. Parasitic insects used in tea plant pest control include Trichogramma (against eggs of the tea small leaf roller and tea tussock moth) and Apanteles (against tea geometrid larvae), etc. In addition, various predatory natural enemies (including ladybugs, lacewings, spiders, and predatory mites) play important natural control effects on various scale insects, tea aphids, and the small green leafhopper.
4 Rationally carry out chemical control to achieve pollution-free production. Chemical control has the characteristics of high efficiency and quick effect, but also has disadvantages such as environmental pollution, pesticide residues, formation of pesticide resistance, and pest resurgence. In the current calls for achieving pollution-free tea production, although the use of chemical pesticides is not completely excluded, higher requirements have also been put forward.
First, in the principles of pesticide use, emphasis should be placed on reducing the amount of chemical pesticides as much as possible. Pesticide requirements should not emphasize their "killing" effect, but should focus more on "regulation." Control should be carried out according to economic thresholds, and those below the threshold may not be sprayed for control.
Second, in the selection of pesticides, varieties with high efficiency, easy degradation, strong selectivity, and lower water solubility should be selected. Pesticides should be selected according to the maximum residue limit (MRL) standards for tea stipulated by the major tea-importing countries at present. The use of dicofol, fenvalerate, and methamidophos in tea production is prohibited, and the use of fenpropathrin, buprofezin, mie man ling, and acephate and other pesticides should be stopped. The use of biological pesticides such as Bacillus thuringiensis preparations (Tianba), Beauveria bassiana, and tea geometrid NPV virus, and botanical pesticides such as rotenone and matrine should be promoted, and lime sulfur mixture should be used rationally. According to the MRL standards currently stipulated by the EU, when chemical pesticides must be used, insecticides such as sedane, phoxim, malathion, bifenthrin, deltamethrin, cypermethrin, and imidacloprid, and acaricides such as propargite and clofentezine may be selected. Third, pesticides must be used strictly according to the stipulated dosage and pre-harvest interval standards, attention must be paid to application quality, and large losses of pesticides should be avoided. Rotation of pesticide use should be advocated. In organic tea gardens, except for biological pesticides and botanical pesticides, no chemically synthesized pesticides may be used.
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