Sun Dongwen,Geng Bo,Kong Fuling,Wang Peilei,Feng Yizhe,Yang Tianyi,Zhang Haijuan

Zibo Vegetable Office,Zibo 255036,China

Abstract Based on years of experience in prevention and control of vegetable diseases and insect pests,three characteristics of infectious diseases of vegetables,including complex symptoms,fast propagation and severe damage,are summarized.The host place,infection way,infection process and prevalence conditions of pathogens are analyzed,and comprehensive,ecological,efficiency principles for the prevention and control of infectious diseases are put forward.Eventually,integrated prevention and control techniques of infectious diseases of vegetables are put forward from five aspects of plant quarantine,agricultural control,physical control,biological control and chemical control.

Keywords Vegetable;Infectious diseases;Control;Technique

Infectious diseases of vegetables lead to abnormal phenomena in internal tissues and external morphology of vegetables due to the infection of pathogenic microorganisms during the growth and development of vegetables.Infectious diseases directly affect the growth and development of vegetables,and further influence the yield and quality of vegetables[1].The main infectious diseases of vegetables are fungal diseases,bacterial diseases,viral diseases and nematode diseases[2].Fungal diseases are the most common diseases,accounting for more than 70% of infectious diseases,while viral diseases are the most difficult to be controlled.

1 Occurrence Characteristics

1.1 Complex symptoms Different vegetable diseases have relatively stable symptoms and certain characteristics,but the same vegetable disease often shows different symptoms due to differences in variety resistance,pathogenic sites,and growth periods of vegetables.Sometimes different diseases show the same symptom,which brings certain difficulties to the diagnosis of vegetable diseases.

1.2 Fast propagation With the upgrade of vegetable varieties and the increase of vegetable seed rearrangement in different regions,the rate at which vegetable diseases are spread by seeds is accelerated.In addition,the demand for water is relatively large during the growth and development of vegetables,which leads to the increase of soil moisture and air humidity in the vegetable field,providing suitable conditions for the occurrence and spread of diseases.

1.3 Severe damage The economic value of vegetables is high.Intensive cultivation of vegetables by farmers improves the nutrition level of vegetable plants,but aggravates the damage of diseases.Moreover,high multiple crop index in vegetable fields provides good environmental conditions for large proliferation and accumulation of viruses,and also aggravates the damage of pathogens to vegetables.

2 Occurrence Regularity

2.1 Parasitic site of pathogens The parasitic sites of vegetable pathogens mainly include soil,manure,seedlings,residual plants.

2.1.1 Soil.Soil is the site for many pathogens to survive winter and summer,and resting spores of some pathogens can survive in the soil for a long time.Generally,low soil temperature and dry environment tend to maintain the dormant state of pathogens and prolong the survival time.

2.1.2 Manure.Pathogens may enter into manure with diseased vegetable plants.In the case of unripe manure,pathogens can be kept alive and brought to the fields as the primary source of infection.

2.1.3 Seedlings.Vegetable seeds are good hosts for pathogens,and asexual reproductive organs often carry pathogens.Pathogens can also go through winter or summer in epidermis,cracks and subcutaneous tissues of vegetable seedlings.

2.1.4 Residual plants.Diseased plant of vegetable is the main place where pathogens directly infect,parasitize and hibernate.Most fungi and bacteria can live in diseased plants for a period of time.

2.2 Propagation mode of pathogens The first is seed and seedling propagation,namely transmission by pathogen-carrying seeds and seedlings.The second is airborne transmission,namely transmission by the movement of air.The third is water transmission, namely transmission by rainfall and watering.The fourth is insect transmission,namely transmission by insects.The fifth is seed propagation;with the rapid expansion and promotion of intensive vegetable breeding,seedlings have become the main vector for long-distance transmission of pathogens.The sixth is mech-anical transmission;with the large-scale application of mechanized operation in the field,machinery has become one of the important ways to spread diseases among different plots.

2.3 Infection process of pathogens The infection of vegetable pathogens can be divided into four stages:contact stage,from the contact of pathogen and vegetable in the infective part to the stage of invasion;invasion stage,from the contact between pathogen and vegetable to the stage of invasion and establishment of parasitic relationship;incubation period,from parasitic relationship between pathogens and vegetables to the stage with obvious symptoms;incidence stage,from the occurrence of harmful symptoms to the end of the whole growth period.

2.4 Prevalence conditions

2.4.1 Host.The hosts mainly are susceptible vegetables with poor disease resistance.Besides,large scale cultivation with high planting density easily results in poor vegetable growth and poor health.

2.4.2 Pathogen.Pathogens have strong pathogenicity and large quantity.

2.4.3 Environmental condition.Climatic conditions,soil environment,biological environment are conducive to the infection and reproduction of pathogens,but not conducive to the growth and development of vegetables and their disease resistance.

3 Control Principles

The prevention and control of infectious diseases of vegetables should adhere to the concept of ecological sustainable development,considering both the economic loss caused by diseases and the negative impact of prevention and control on the environment.Therefore,a variety of factors should be taken into comprehensive consideration in the process of prevention and control,and various governance measures should be adopted to maximize the overall effect and control the damage of pathogens below the economic threshold level.

3.1 Comprehensive principle In order to effectively control the losses caused by diseases,agricultural,physical,biological and chemical control measures should be integrated to control the diseases.

3.2 Ecological principle Taking vegetable base as an ecosystem,the correlation among various ecological factors is comprehensively analyzed according to the mutual relationship between pathogen,vegetable and environment,and the overall situation between ecological balance and control effect is weighed to guide disease control.

3.3 Principle of efficiency Economic,ecological and social benefits should be comprehensively considered to control the occurrence and damage of vegetable diseases with minimum human and material input and obtain maximum economic benefits.Meanwhile,it is also necessary to maintain ecological balance and avoid the harm to consumers caused by pesticide application.

4 Integrated control technique

4.1 Plant quarantine It is an important measure to ensure safe production of vegetables by quarantining vegetable seeds and seedlings and controlling the spread of dangerous diseases.The importation of dangerous diseases with vegetable seeds and seedlings from other places should be prohibited.The dangerous diseases occurred locally should be blocked in a certain area to prevent their expansion and spread,and active measures are taken to extinguish these diseases.When dangerous diseases are introduced into a new area,they must be eradicated completely by forces from all sides.

4.2 Agricultural control According to the relationship between vegetable field environment and pathogens,some target factors are changed to control the occurrence and damage of diseases,so as to achieve the purpose of controlling diseases and protecting vegetable production.

4.2.1 Selecting disease-resistant varieties.Planting disease-resistant vegetables is the most effective way to prevent and control diseases[3],and it is also the most economical and effective method,especially for some vegetable diseases that are difficult to control.

4.2.2 Cleaning gardens.The residual plants in vegetable fields are removed to destroy the environment for pathogen reproduction and overwintering.Field weeds,especially perennial weeds,are the sources of primary infection of some vegetable pathogens,so it is necessary to eradicate field weeds in a timely manner.

4.2.3 Crop rotation.Crop rotation can make balanced use of soil nutrients,improve soil performance and fertility,and control disease at the same time.Water and drought rotation has good control effect against some soil-borne diseases,such as blight of solanaceous and melon vegetables.

4.2.4 Ploughing.Ploughing affects the living environment of pathogens.Deep tillage and soil improvement have good effect on controlling soil-borne diseases.Ploughing will turn pathogens originally under the soil layer to the surface.Due to the changes in light,temperature and humidity,resting body of pathogens will lose the favorable conditions for germination and infection once exposed to the soil surface.Meantime,pathogens carried by diseased vegetable residues in the ploughed soil are easily decomposed by saprophytic bacteria.4.3 Physical control Vegetable diseases are controlled by changing environmental conditions to inhibit or kill pathogens.For example,bed-planting and plastic film mulching can reduce the field humidity and control the occurrence of diseases;high temperature tightly greenhouse in summer can kill pathogens in the soil.

4.4 Biological control Antagonism and cross protection between microorganisms are mainly utilized in biological control.Antagonism is to kill or inhibit the occurrence and damage of pathogens through antagonistic mechanisms of antibiosis,parasitism and competition.Cross protection is to induce disease resistance of vegetables and even protect the vegetables from invasion of pathogens by inoculating pathogens with low pathogenicity.

4.5 Chemical control Chemical control is featured by quick and effective effect,and it can not be replaced by other prevention and control measures.However,chemical control also has great limitations.For example,chemical control will pollute the environment and bring pesticide residues,thus affecting people’s health.The following aspects should be paid attention in chemical control:pesticides with high efficiency,low toxicity and low residue are used,while pesticides banned by the state in the production of vegetables are strictly prohibited;chemical pesticides should be rotated to improve their prevention efficiency;safety interval must be paid attention when applying pesticides.