Microecological Prevention and Control Technology of Facility Strawberry Continuous Cropping Diseases and Its Application Effects

Houjun HE, Jiexu HUANG, Xiaolin WANG, Yushan QIAO, Muxiang JI*

1. Jurong Heshan Family Farm Co., Ltd., Jurong 212400, China; 2. Zhenjiang Institute of Agricultural Sciences in Hilly Areas of Jiangsu, Jurong 212400, China; 3. Nanjing Agricultural University, Nanjing 212095, China

Abstract In order to actively develop green ecological strawberry, the authors have studied integrated microecological prevention and control technologies of strawberry continuous cropping diseases, including increasing soil biomass and solar high temperature disinfection during strawberry greenhouse leisure period in summer, biological fertilizer (agent) treatment before colonization, root irrigation treatment with biocontrol agent, as well as appropriate amount of fulvic acid and cytex after colonization, forming a supporting technical system for the microecological prevention and control of soil-borne diseases in facilities. The demonstration application in production shows that the technology has the functions of restoring and enhancing soil biological fertility, enriching beneficial microbial flora, antagonizing harmful bacteria, significantly promoting the growth and development of strawberry, reducing the incidence of soil-borne diseases, reducing the use of chemical fertilizers and pesticides, promoting the early ripening and high yield of strawberry, significantly improving the quality and flavor of strawberry, reducing the risk of pesticide residues, and boosting consumer confidence, which further improves the economic benefit, social benefit and ecological benefit, with good application prospect in production.

Key words Strawberry; Continuous cropping disease; Microecology; Prevention and control technology

1 Introduction

Since benefits are realized in the same year with high return and picking and sightseeing functions, strawberry has become an important characteristic economic pillar of modern agricultural development and rural revitalization in major producing areas in China. With the improvement of people’s living standard and the change of consumption concept, the majority of consumers’ demand for agricultural products has changed from "excellent quality and reasonable price" to "high quality and safety", so the development of strawberry industry is gradually turning to green and efficient production. In order to solve the problems of soil deterioration, environmental pollution, increased disease resistance, decreased fruit quality and pesticide residue caused by blind over-input of chemical fertilizers and pesticides in traditional strawberry production[1-2], scientific research institutes and government enterprises have developed and promoted a large number of green prevention and control technologies.

Continuous cropping of strawberry has gradually become the planting structure of strawberry main producing areas. Continuous cropping diseases of strawberry caused byFusariumoxysporum,Verticilliumdahliae,Phytophthoraspp. andPythiumspp. have posed serious threat to strawberry production, especiallyFusariumwilt, anthracnose, root rot and other soil-borne diseases are the main diseases in strawberry production. Pathogen-bearing soil and seedlings are important sources of disease infection. When the environmental conditions are suitable, the pathogens spread with the help of infected mother plants, soil, water and farm tools, and invade from wounds or directly from the epidermis and hair of young roots[3-4].

At present, prevention is still the major means against strawberry diseases caused by continuous cropping, and it is difficult to control the diseases once they occur. The prevention and control of strawberry continuous cropping diseases mainly rely on closed fumigation treatment of continuous cropping soil with agents such as dazomet, lime nitrogen and metham-sodium before planting. Although these agents have good effects on soil-borne diseases, it is difficult to improve the soil, and long-term improper use is easy to cause the damage of soil aggregate structure and the deterioration of soil properties such as compaction, and their use cost is high. In addition, root treatment with hymexazol, carbendazim and other chemical agents can also achieve certain control effects, but the development of pathogen resistance and environmental pollution make this control method difficult to meet the needs of sustainable development of strawberry production[5-6]. At present, the prevention and treatment of strawberry diseases by means of crop rotation, antagonistic soil microorganisms and VAM fungi (Vesicular-Arbuscular Mycorrhizae) have been extensively studied at home and abroad[7-8]. However, the effect of biological control is often unstable due to the difficulty of colonization of beneficial microorganisms in soil and improper use of technology. Solar high temperature disinfection is to kill pathogens in soil by high temperature closed shed[9], but due to complex soil environment, great differences in treatment methods and annual climate of different places and other reasons, the effects vary greatly. With the improvement of people’s requirements for the safety and quality of agricultural products and the enhancement of environmental awareness, it has become an inevitable trend of agricultural development to reduce the use of chemical fertilizers and pesticides and develop green ecological agriculture. According to the experiment and demonstration in recent years, the integrated application of microecological prevention and control technology for strawberry continuous cropping diseases has achieved good results, which is of great significance for promoting the healthy and sustainable development of strawberry industry.

2 Key technologies and application methods

2.1 Solar high temperature disinfection during strawberry greenhouse leisure period in summer

2.1.1Increased application of organic materials and functional microbial agents after clearing the shed and planting. In late April or early May, plants are pulled out immediately after strawberry harvesting, and ground covers such as black mulch are removed. The residual diseased plants of strawberry root rot and anthracnose should be removed, and healthy and disease-free plants are retained and plowed into the soil. It is recommended to broadcast corn or mustard seeds, and strengthen the management of water and fertilizer after proper shallow rotation. Generally before the middle of July, when corn plants grow to more than 1 m high or mustard plants are blooming, they should be smashed and ploughed into the soil in time, and supplemented with 1 000 kg/667 m2high-quality livestock and poultry manure or 200 kg/667 m2vegetable cake (or 300-500 kg/667 m2rice bran), which will have a better fertilizing effect. If corn or mustard has not been planted, 1 000-2 000 kg/667 m2mushroom residue or vinegar residue can be applied, supplemented with 1 000 kg/667 m2high-quality livestock and poultry manure, or 200 kg/667 m2vegetable cake, or 300-500 kg/667 m2rice bran. Special bacterial agent for closed shed resistant to high temperature can be evenly broadcasted at the dose of 20-30 kg/667 m2, and ploughed into the soil by mechanical or artificial methods, while residual healthy plants and high-quality organic materials are stirred into the soil.

2.1.2Moisturizing and sealing shed, solar high temperature and high humidity treatment. Agricultural films are covered on the ground surface inside the shed, and the furrows inside and around the shed are irrigated with sufficient water. The greenhouses are tightly covered with film and compacted with soil to prevent air from entering. The organic matter fermentation consumes oxygen in the soil, so that the soil is in a state of anoxia for a long time. Combined with solar high temperature treatment in summer, the soil temperature can reach up to 50-60 ℃, and the soil can be reduced and disinfected at high temperature to kill pathogens and compost organic materials in continuous cropping field. Continuous high temperature reduction and disinfection treatment lasts 20-30 d.

2.1.3Removing the film covering the greenhouses and the ground. After high temperature reduction and disinfection treatment is fully carried out, the film covering the greenhouses and the ground surface is uncovered as soon as possible, so that the reduced soil can mature and oxidize as soon as possible to restore the vitality.

2.2 Application of biological fertilizer (agent) before and after colonization

2.2.1Biological fertilizer (agent) treatment when ridging before colonization. From the end of August to the beginning of September, generally 5-8 d before colonization, fully decomposed organic fertilizers are supplemented when ditching and ridging according to the soil capacity and other conditions. In addition to appropriate calcium magnesium phosphate or superphosphate, and slow-release fertilizer, it is necessary to increase the application of biological fertilizer (such as 80-120 kg/667 m2biological fertilizer containing ≥ 200 million cfu/gBacillussubtilisandB.mucilaginosus), combined with 200 million spores/gTrichodermaWP (dose 2-3 kg/667 m2), or 5 kg/667 m2compound microbial agent (such as EM bacteria), and evenly broadcasted in fine soil or organic fertilizer. The moisture of ridge surface is kept at a certain level, and the shed is covered with 50% sunshade net, which is conducive to colonization and multiplication of microbial bacteria in the soil, enhances soil biological fertility, and antagonizes harmful bacteria in the soil.

2.2.2Root treatment with biocontrol agents. During colonization, 100 billion live spores/gB.subtilis200-300 times dilution, or 200 million live spores/gTrichoderma30-50 times dilution, or 1×106live spores/gPythiumoligandrum500 times dilution can be selected. The roots of suspected infected strawberry seedlings can be dipped in appropriate concentration of low-toxic chemical agents such as pyraclostrobin or fludioxonil·metalaxyl-M for 10 min before transplanting.

2.2.3Root irrigation with biocontrol agents After colonization for 5-7 d, 500 million CFU/gPaenibacilluspolymyxaAS 200-300 times dilution, or 200 million spores/gTrichodermaWP 300-500 times dilution, or 100 billion CFU/gB.subtilisWP 500-1 000 times dilution, or EM biological agent 500 times dilution, or Ningdun 2 biocontrol agent 200-300 times dilution, or 1×106spores/gP.oligandrum5 000-7 000 times dilution, combined with appropriate amount of mineral fulvic acid, potassium, seaweed fertilizer (dose 3-5 kg/667 m2) can be used to irrigate or flush the roots for 2-3 times with an interval of 15 d, 100-200 mL water each plant.

3 Application effects and discussion

3.1 Application effectsIn the past two years, the microecological prevention and control technology of strawberry continuous cropping diseases in Jurong strawberry production area of Jiangsu Province was compared with the conventional production shed. The results showed that in demonstration shed for microecological prevention and control of strawberry continuous cropping diseases, soil compaction, acidification and salinization were alleviated; the seedling mortality caused by soil-borne diseases was reduced by 30%-40%; the fertilizer and pesticide consumption was reduced by 35%-45%; and the application frequency was reduced by 30%-40%. The yield of commercial strawberry fruit increased by more than 20% on average, among which the proportion of high-quality fruit with single fruit weight of 20 g or more increased by 15%-20%. Due to excellent quality of fresh fruit, good flavor and greatly reduced pesticide residues, it increased consumption demand, and promoted the development of agricultural tourism and sightseeing picking. The average price of strawberries in demonstration sheds was 40-60 yuan/kg, which was 10-20 yuan/kg higher than that in conventional production shed. The quality and efficiency was increased by 20%-30%. The technology not only realized high economic, social and ecological benefits, but also promoted the green transformation and upgrading of strawberry industry in this region.

3.2 DiscussionWith the increase of strawberry continuous cropping years, the species and quantity of harmful fungi in soil have increased significantly, and the microbial flora in soil is the main driving force of crop metabolism. The increase of harmful pathogens causes various diseases of strawberry. Yin Xiaominetal.[10]put forward that diseases play a dominant role in all continuous cropping obstacles, especially soil-borne diseases, and some harmful fungi that have never been found will also have adverse effects on strawberry roots. Zhu Jiehuaetal.[11]proposed that the pathogenic fungi causing strawberry continuous cropping obstacle mainly includeFusarium,Rhizoctonia,Verticillium,Phytophthora,Pythium,PestalotiopsisandColletotrichum. Zhang Meishenetal.[12]suggested that continuous cropping of the same crop could enrich some specific microbial communities, especially plant pathogenic fungi, which was not conducive to the balance of microbial populations in soil, but provided a good hotbed for the occurrence of plant root diseases. Wu Jiazhietal.[13]held that heavy application of pesticides resulted in the destruction of crop growth environment, which had a great adverse impact on microbial population in soil and beneficial microorganisms such as azotobacter, rhizobium and organic-decomposing bacteria in soil. In addition, excessive application of chemical fertilizer in strawberry facility cultivation also led to the reduction of pathogen antagonism in soil, thus promoting the propagation of pathogenic bacteria and aggravating the occurrence of soil-borne diseases[14]. In recent years, micro-ecological prevention and control technologies of strawberry continuous cropping diseases have been integrated, including increasing soil biomass and solar high temperature disinfection during strawberry greenhouse leisure period in summer, biological fertilizer (agent) treatment before colonization, root irrigation treatment with biocontrol agent, as well as appropriate amount of fulvic acid and cytex after colonization, forming a supporting technical system for the prevention and control of soil-borne diseases in facilities. The demonstration application in production shows that the technology has the functions of restoring and enhancing soil biological fertility, enriching beneficial microbial flora, "activating" soil, antagonizing harmful bacteria, greatly reducing the seedling mortality of strawberry, promoting the growth and development of strawberry, reducing the use of chemical fertilizers and pesticides, promoting the early ripening and high yield of strawberry, significantly improving the quality and flavor of strawberry, reducing the risk of pesticide residues, and boosting consumer confidence, so it has good application prospect in production.