Development and Application of Green Pest Control Technology in Tea Garden

Zongmao CHEN

Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310008, China

Abstract A discussion on the necessity of green control of tea pests in tea gardens was conducted on the basis of the development process from traditional control, chemical control to green and ecological control. The connotation of green control in tea gardens was analyzed, and physical control and chemo-ecological control, biological control and agricultural control respectively were introduced. Besides, the rational selection and precise use of pesticides were proposed and current problems in the green control of tea gardens in China were introduced.

Key words Tea pests; Green control; Reasonable use of pesticides

1 Introduction

Tea trees, native to southwest China, have been planted for more than 3 000 years. Tea is universally recognized as a drink beneficial to human health. With people’s continuous pursuit of quality of life, the requirements for tea quality and safety are also improving.

Compared with other crops, tea tree has the following characteristics. First, tea tree is a perennial evergreen plant, and the environmental pollutants will accumulate year by year in tea garden and tea trees. Due to the large leaf area of tea buds and leaves, there will be higher original deposition of pesticides or adsorption of higher concentration of environmental pollutants under the condition of using the same dose of pesticides and the same concentration of pollutants in the air. Second, compared with other crops, tea trees are picked several times a year, with short safety interval after pesticide application and little degradation time of pesticide. Third, tea leaves are immediately processed into dry tea after picking and soaked directly when drinking, and pesticide residues and other pollutants in tea leaves will be soaked in tea water more or less according to their solubility in water. Therefore, the ecological environment of tea garden and the quality and safety of tea have attracted more attention[1].

Pests have brought certain harm to tea industry. There are more than 800 species of pests on tea trees, more than 400 of which are common species. There are about 140 species of diseases on tea trees. In China, a total of 421 species of weeds have been reported in tea gardens. Pest control in tea garden is an important support to protect tea production safety, ensure tea quality safety and promote sustainable development of tea industry.

2 Development of pest control technology in China

Over the past 70 years since the founding of the People’s Republic of China, the succession of pests and application of control technology in tea gardens in China can be divided into the following stages.

2.1 Traditional control stageBefore the 1940s, tea gardens were scattered in China. There were relatively few disasters of pests in tea gardens, and the control technology was relatively backward. Since the founding of the People’s Republic of China, tea production had achieved rapid development, but the pest control of tea garden was still in the stage of agricultural control and the use of botanical pesticides. From the standard of ecology, although it was technically in the primitive stage of development at that time, the quantity of harmful and beneficial species in production was relatively balanced.

2.2 Chemical control stageThe invention of the insecticide DDT in 1938 ushered in the use of chemicals to control pests and diseases. Organochlorine pesticides were first used in tea production, followed by organophosphorus pesticides in the 1960s and pyrethroid pesticides in the middle and late 1970s, and neonicotinoid pesticides began to be popularized and applied in tea production in the early 21stcentury.

In the late 1960s, the toxicity of chemical pesticide residues and the resistance of pests to pesticides aroused people’s concern. The use of organochlorine pesticides and neonicotinoid pesticides had been banned and discontinued in tea gardens; organophosphorus pesticides were not widely used in general, while rogor, dichlorvos and quinalphos had been discontinued; pyrethroid pesticides were still in use except for fenvalerate, which had been banned.

Although chemical pesticides are still used in tea production, the overall trend is decreasing. For example, due to high water solubility, 80%-90% of neonicotinoid pesticide residues in tea leaves will be dissolved into tea water. Meantime, the use of neonicotinoid pesticides has reduced bee populations by 50%-60% in many countries, thereby reducing crop yields. European countries have proposed a Europe-wide ban on the use of 3 neonicotinoid pesticides (imidacloprid, thiamethoxam and dinotefuran) on any crops in the field and have set a very strict maximum residue limit (MRL) of 0.05 mg/kg in tea.

In general, although the widespread use of chemical pesticides in tea production improves the control effect of pests, it also causes the problem of pesticide residues and the risk of tea quality and safety, and leads to the decrease of beneficial insect population and the increase of pest population in some areas. From the 1960s to the 1990s, there were 5 large-scale pest population successions in China’s tea regions (Table 1), 3 of which were caused by the change of pesticide category[2].

Table 1 Factor analysis of 5 pest population successions in China’s tea gardens

From the late 1950s to the early 1960s, the promotion and application of organochlorine pesticides in tea regions once increased pesticide residues in tea, becoming a restricting factor for tea export. In the middle 1960s, the outbreak of scale pests such asLeucaspisjaponicaCockerell appeared in the tea regions of China, which was the first significant change of pest population succession in large area tea gardens in the tea regions of China.

From the 1960s to the early 1970s, organophosphorus pesticides were promoted in vast tea regions to replace organochlorine pesticides. Although scale pests on tea trees were sensitive to organophosphorus pesticides, organophosphorus pesticides had a strong lethality to the predators of various mites in tea gardens (such as ladybugs), but not to the eggs of various mites. Therefore, in the middle and late 1970s after the extensive use of organophosphorus pesticides, mites became another new group subsequent to scale pests, which was the second significant change of pest population succession in tea gardens in China.

In the middle 1970s, pyrethroid pesticides were widely applied in tea gardens. These pesticides had a long residual effect and had strong killing effect on the natural enemies of pests. Therefore, within the 5-10 years after pyrethroid pesticides were widely used, the prevalence and rampant occurrence ofAleurocanthusspiniferus(Quaintance), a piercing-sucking mouthpart pest, successively appeared in a wide range of tea regions in China. This was also the third significant change of pest population succession in tea gardens in China caused by pesticide application[2]. As for the fourth and fifth succession changes of pest populations, they were mainly caused by the changes in cultural practices.

2.3 Introduction of the concepts of green prevention and control and ecological regulationDuring the 50 years from the founding of the People’s Republic of China to the end of the 20thcentury, the composition, transition and succession of pest flora in tea gardens were actually the development and change process of "competition-balance-re-competition-rebalance" of pests and natural enemies in the tea garden ecosystem. Unfortunately, the succession of the above-mentioned tea pests all appeared in the process of management, and it was not what people expected or hoped.

The purpose of disease and pest control in tea garden is to avoid the economic loss of tea caused by pests. People gradually realize that in the process of control, it is necessary to consider the rampancy of secondary pests, the impact on beneficial organisms, and environmental pollution. Therefore, a review of the 50 years of pest control experience in tea gardens shows that people must attach importance to the principles of sustainable development and coordinated symbiosis, high efficiency and harmony while controlling pests[3]. The concept of ecological regulation should be used to replace the concept of eliminating pests when controlling pests. From the 1980s to the 1990s, ecological control techniques aimed at minimizing chemical pesticides had been successively proposed in the world.

3 Technical connotation and implementation of green prevention and control in tea garden

Generally speaking, the use of pesticides in tea production increases the quality and safety risks of tea, and may lead to excessive pesticide residues in exported tea. Moreover, heavy use of pesticides in tea gardens is easy to kill non-target organisms and destroy the balance of the ecosystem in tea gardens. In addition, pesticide application can lead to a rapid increase in pest resistance, thus increasing the pressure of field control. This series of problems warns that the reduction of chemical pesticides in tea production is an irresistable trend. Since the beginning of the 21stcentury, the concept of green prevention and control has gradually gained popular support.

In 2006, the Ministry of Agriculture put forward the concept of "public plant protection, green plant protection and scientific plant protection", in order to implement the national development strategy of "changing mode and adjusting structure" in the new era. Green prevention and control aims to promote agricultural safety and reduce the consumption of chemical pesticides, and controls the behavior of pests by adopting chemo-ecological control, agricultural control, biological control, physical control, scientific drug use and other environmentally friendly measures. From the perspective of tea as a healthy crop, green prevention and control technology can not only reduce the population quantity of pests in tea garden, but also control pesticide residues in tea and pollutants in tea garden environment, so as to improve the quality and safety of tea in China.

Since 2015, the tea plant pest control innovation team of Tea Research Institute, Chinese Academy of Agricultural Sciences began exploratory research on green prevention and control of pests in tea garden, and controlled tea garden pests by agricultural control, physical control, biological control, chemo-ecological control and other methods, so as to realize the purpose of controlling pest population without or with less consumption of pesticides, protecting population quantity of beneficial organisms and, ensuring the quality and safety of tea products.

3.1 Physical controlThe physical control technology is designed based on the principle of the tropism of insects to specific light waves, lights, and colors, and uses light trap and color board to trap and kill pests. At present, there are yellow and red sticky boards (trappingEmpoascaflavescensand various thrips in tea gardens), blue sticky boards (trapping various thrips) and green sticky boards (trapping leafhoppers) used in tea gardens. In recent years, the wide wave lamps have been changed to narrow wave lamps for targeted pests, which reduce the manslaughter of natural enemies.

3.2 Chemo-ecological control

3.2.1Pheromone control techniques. chemo-ecological is the generic terms of compounds that communicate chemically between organisms. In short, pheromone control technology is to trap, avoid or interfere with the behavior and mating of pests by using synthetic volatile substances, in order to achieve the purpose of prevention and control. For example, the sex pheromone control technology of inducing and killing pests is set up in fields by artificially simulating and synthesizing the compounds that female insects release to attract males of the same species. Since 2005, the Tea Research Institute of Chinese Academy of Agricultural Sciences has successively carried out analysis, identification, synthesis and field application of sex pheromones of tea pests, such asEctropisobliquahypulina,Ectropisgrisescens,Euproctispseudoconspersa,Caloptiliatheivora,Dasychirabaibarana,Prodenialitura,Andracabipunctata,etc.Now the promotion area has reached hundreds of thousands of hectares, and the technique is very popular with tea producers.

In addition to sex pheromones, there are aggregation pheromone prevention and control techniques. The use of some small pests such as thrips that will secrete aggregation pheromone and form population aggregation can also achieve the purpose of centralized control.

3.2.2Application of plant volatile attractant. Plant volatile is the "language" of plants[4]. Plants in different states will release different volatile components, to send different communication signals to other organisms. For example, when visiting the tea garden in early spring, people can feel the faint smell of tea, which is a signal of "good health" to the outside world after the tea trees have rested in winter. The tea trees will release volatile components if infected by diseases and pests, to send "help" signals to the outside world. Information exchange between organisms in nature has developed into a new discipline in modern science[5], so the application of information exchange in green prevention and control deserves attention. The Tea Research Institute of Chinese Academy of Agricultural Sciences had ever conducted tests at a test site in Shaoxing, Zhejiang Province; sinceAeolesthesindutaoccurred severely in local tea gardens, researchers developed a cheap attractant with volatile compounds of tea trees (namely 5-6-carbon alcohols and aldehydes), vinegar, yellow rice wine and sugar, which had good attractant effect onA.indutawhen putting in a basin in the tea garden. More than 330 000A.indutahad been trapped by this kind of pest attractant in tea gardens for consecutive 3 years, and further tests are under way. It can be expected that in the next 5-10 years, it will become an important chemo-ecological green prevention and control technology in tea gardens by utilizing the attractant effect of various volatiles[6].

3.3 Biological control

3.3.1Utilization of natural enemies. Natural enemies include predators and parasites. The parasites means that the natural enemy lays eggs in the eggs, larvae, pupae or adults of pests, resulting in the death of pests, such as various parasitic wasps and flies. The predators refer to those eliminate pests by hunting, such as ladybugs. The purpose of prevention and control can be realized by protecting, introducing and releasing natural enemies in tea gardens.

3.3.2Utilization of biopesticides. Biopesticides are preparations that use living organisms (fungi, bacteria, viruses) or their metabolites to kill pests. BT preparation,BeauveriabassianaandMetarhiziumanisopliaeare widely used in tea gardens, which are mainly used to control Lepidoptera defoliators (such asE.obliquahypulina,E.grisescens,E.pseudoconspersa,P.litura) and weevils. Botanical insecticide, such as pyrethrin, rotenone and virus preparations ofE.obliquahypulina, had been widely used in tea gardens in the 1980s. Since the 21stcentury, the virus preparations ofE.obliquahypulina, matrine, azadirachtin and veratrine have also been widely used in tea production.

3.4 Agricultural controlAgricultural prevention and control is an ecological control method based on improving the ecological environment of tea garden, taking agricultural measures as the leading and focusing on biological and ecological theories. This method will gradually develop into an important measure for pest control in tea gardens by improving the natural control ability to achieve a relative balance between the quantity of pests and natural enemies. Therefore, tea trees should be planted in mountainous regions with superior ecological conditions, and tea trees with strong resistance to diseases and pests are selected. In Japan, the Yabukita variety accounts for about 75% of the tea garden area, but it has weak resistance to anthracnose andPseudaulacaspispentagona. The widespread popularization of Yabukita led to the prevalence of anthracnose in tea gardens throughout Japan, which became a profound lesson in the history of the world tea industry[7-8].

Tea gardens can be surrounded by a protective forest of tall plants to prevent pests from entering and migrating. The author saw many tea gardens surrounded by tall tree species in Shandong Province, which had certain effect on reducing diseases and pests. In addition, some plants that attract natural enemies can also be planted between rows of tea gardens to create the habitat environment for natural enemies, so as to improve the diversity of natural enemies and achieve the purpose of pest control.

The results showed that high nitrogen fertilization would cause obvious changes in diseases and pests in tea gardens, and the occurrence of small pests would increase. Phosphorus and potassium fertilizer should be increased properly in tea gardens, which will increase the resistance of tea trees to pests, especially the pests with small piercing-sucking mouthparts and sucking mouthparts.

3.5 Rational selection and accurate use of pesticidesGreen prevention and control aims to adopt safe and effective measures for the comprehensive management of pests, without or with less consumption of chemical pesticides, focusing on reasonable selection and accurate application of pesticides. High toxic pesticides and water soluble pesticides should be forbidden in tea production.

Drinking tea is different from ingesting other foods. Generally, people only drink tea water and discard the tea residue completely. If there are pesticide residues in dry tea, when drinking the same amount of dry tea, the pesticide with high water solubility is dissolved into the tea water in a high amount, and is absorbed into the human body in a high amount. Some pesticides have high solubility in water, such as imidacloprid, acetamiprid, dinotefuran, thiamethoxam,etc.; 80%-90% of the residues of these pesticides in tea can be transferred from dry tea to tea water, resulting in safety risks, so they are not suitable for application in tea gardens. In addition, new scientific research has proved that several organophosphorus pesticides widely used in the past (such as rogor, fenitrothion,etc.) are very water-soluble and should be withdrawn from the tea industry from the perspective of safety. The Tea Research Institute of Chinese Academy of Agricultural Sciences had determined the tea samples randomly sampled from 6 kinds of tea in all the tea-producing provinces of China for consecutive 14 years, and the results showed that the water-soluble pesticides, imidacloprid and acetamiprid, had exceeded the standard. Although the situation has been improved in recent years, there is still a high detectable rate. Therefore, the author suggests that neonicotinoid pesticides and other pesticides with high solubility in water should not be used in tea gardens to ensure the safety and health of tea drinkers.

Recently, the tea plant pest control innovation team of Tea Research Institute, Chinese Academy of Agricultural Sciences selects a new pesticide "Sefina" produced by BASF cooperation, which is a new compound formed by soil microorganisms in artificial incubator. Studies found that "Sefina" sprayed at the dose of 25 mL/667 m2had good control effect onE.flavescens, and there were only 0.2-1.0 mg/kg of pesticide residues when fresh leaves were picked at 7 d post spraying and then processed into dry tea. The water solubility of the pesticide is only 25 mg/L, so there is almost no residue in tea water. The use of similar low water soluble pesticides in tea gardens is conducive to the safety of tea drinking.

4 Problems in green prevention and control of tea garden

In recent years, the promotion of green pest control in tea gardens has been intensified, and the promotion area has been expanding year by year. The green prevention and control technology has been promoted and applied in tea gardens of about 30 000 hm2in 9 provinces including Zhejiang, Fujian, Anhui, Sichuan, Hunan, Hubei, Jiangxi, Jiangsu and Hainan, and achieved good results. When the consumption of pesticides is reduced by 70%-100%, the yield of tea garden is increased by 15%. But from the implementation process of a few years, there are still several problems as follows.

4.1 Science and technology support at the national level is insufficientGreen prevention and control should be the direction of pest control for some time in the future, but the overall development level is not fast enough, because the investment in scientific research is not enough and there is insufficient support at the national level for long-term and continuous scientific and technological projects for green prevention and control. It is suggested that the state, ministry and province should support green prevention and control by crops and regions, establish several green prevention and control demonstration sites for each crop and promote for 3-5 consecutive years, and establish special funds to support innovation of new green prevention and control technologies.

4.2 Innovation in green prevention and control technologies is not strong enoughOverall, the innovation of green prevention and control technology in China is not enough. Innovation and research should be strengthened from the following three aspects: strengthen the research and development of biological control technology and biopesticides; strengthen the research of chemo-ecological technology, and use plant volatiles for pest population control from the study of background value of volatiles in tea garden; strengthen molecular biology research, to seek transgenic insect control technology.

4.3 Quality standardization of green prevention and control products needs to be strengthenedAt present, there are still many problems in the quality of green prevention and control products, and the quality of botanical pesticides as substitutes for chemical pesticides is uneven. According to the detection, some botanical pesticides are added with chemical pesticides, for example, many matrine products are added with chemical pesticides to improve the control effect, and some products have insufficient content of effective ingredients. It is suggested that the relevant government departments should strengthen the quality inspection and management of botanical pesticide products to ensure the quality of green prevention and control products.