Plant Disease Epidemiology & Tree Diagnosis PDF

DMMMSU-CAFF PLANT DISEASE EPIDEMIOLOGY 1 Reymark P. Rivera, RPF Faculty, CAFF EPIDEMIC When a pathogen spreads to and affects many individual; within a certain area and within a relatively short time, this type of phenomenon is called an epidemic. Any in...

DMMMSU-CAFF PLANT DISEASE EPIDEMIOLOGY 1 Reymark P. Rivera, RPF Faculty, CAFF EPIDEMIC When a pathogen spreads to and affects many individual; within a certain area and within a relatively short time, this type of phenomenon is called an epidemic. Any increase of disease population. 2 the dynamics of change in plant disease in time and space 01 An epidemic has been defined as any increase of disease in a plant population.  EPIDEMIOLOGY The study of epidemics and of the factors that influence them. It deals with the interaction of host, pathogen and environmental factors that leads to an epidemic disease. study of the occurrence and cause of 3 infectious diseases, their origin, and their distribution in space and time within a population. 01  EPIDEMIOLOGY Plant disease epidemics sometimes called epiphytotic, occur annually on most crops in many parts of the word. Most epidemics are more or less localized and cause minor to moderate losses. Epidemiology is concerned simultaneously 4 a. populations of pathogens b. host plants c. environment ELEMENTS/COMPONENT OF AN EPIDEMIC Plant disease epidemics develop as a rusult of the timely combination of the elements that result in plant disease: 1. In fungal & bacterial diseases Susceptible host plants A virulent pathogen Favourable environmental conditions over a fairly 5 long period of time. Human may unwittingly help to initiate and develop epidemic through some of their activties (e.g. by topping or pruning in wet weather). ELEMENTS/COMPONENT OF AN EPIDEMIC 2. In virus & virus like diseases The virus The host The vector Environment 6 Factors effecting the development of disease epidemic 1. Host factors 2. Pathogen factors 3. Environmental 4. Effect human cultural practices and control measures (human activities) 5. Time factors 7 8 Host factors 1. Level of genetic resistance or susceptibility of host 2. Degree of genetic uniformity of host plants\ 3. Type of crop 4. Age of host plants 5. Population density and structure 6. General plant health9 7. Introduction of new host 8. Introduction of new alternate host Host factors 1. Level of genetic resistance or susceptibility of host  Highly resistant  Moderately resistant  Susceptible  Vertical resistance (monogenic, host specific)  Horizontal resistance (polygenic, more durable) 10 Host factors 2. Degree of genetic uniformity of host plants  Monoculture  New strains are developed 11 Host factors 3. Type of crop  Annual crops  Perennial crops  Annual crops and foliar or fruit disease develop much more rapidly (in weeks)  perennial woody diseases take longer time to develop (in years) 12 Host factors 4. Age of host plants  Plants change it resistance and susceptibility with age  Some plants are susceptible only during growth period and become resistant during mature period  The change of resistance with age is known as ontogenic resistance 13 Host factors 5. Population density and structure  Large number of host to the pathogen  Large area to reproduce 6. General plant health  Weaker the plant disease will be more 14 Host factors 7. Introduction of new host  Source of primary inoculum to the next crop  Determine the course and intensity of n epidemic 8. Introduction of new alternate host 15 Pathogen factors 1. Presence of pathogen 2. Levels of virulence 3. Quantity of inoculums near hosts 4. Type of reproduction of the pathogen 5. Ecology of the pathogen 6. Mode of spread of the pathogen 7. Introduction of new pathogen 16 8. High birth and low death rate 9. adaptability Pathogen factors 1. Levels of virulence a. Highly aggressive  High level of virulence more inoculum  Disease epidemic faster b. Moderately aggressive (disease spread moderately) 17 c. Poorly aggressive  Lesser inoculum  Disease in several years Pathogen factors Quantity of inoculums near hosts  Greater the number of propagules greater will be the rate of disease  Greater the inoculum greater will be the disease  Inoculum is less in quantity then the disease never occurs 18 Pathogen factors Type of reproduction of the pathogen a. Based on reproductive cycle  Polycyclic – cause sever epidemics; produce many generations in a single growing season; more inoculum production  Monocyclic – takes many of years to develop in epidemic; produce only one generation in a year; 19 complete only one cycle in one year or growing season b. Based on type of reproduction  Sexual(oospores, ascopores)  Asexual (conidia, zoospores) Pathogen factors Ecology of the pathogen a. Depends on the type of pathogen  Ectoparasites – inoculum produce on the aerial parts of the host; spores and seeds disperse with ease over a range of distance and cause epidemics.  Endoparasites – pathogen can be systemic in 20 nature produce inoculum in the system of host; spread of pathogen is rare without vectors. Pathogen factors Mode of spread of the pathogen  Survival efficiency - air borne - soil-borne - vector-bornes  Dispersal efficiency - passive dispersal (in km) (field tool and 21 instruments, air, wind, irrigation water, soil etc.), - active dispersal (in cm) Environmental factors 1. Aerial environment 2. Edaphic environment 3. Some other factors  wind  Air pollution  Herbicide damage 22 Environmental factors 1. Aerial environment  Temperature  Moisture (dominant factor in diseases caused by oomycetes, fungi, bacteria and nematodes 2. Edaphic  Soil temperature 23  Soil ph  Soil water content  Soil fertility  Soil organic matter content Human Activities 1. Have a direct or indirect effect on disease epidemics. 2. Favorable and unfavorable for a disease epidemic 3. Some of the are:  Site selection and preparation  Selection of propagative material  Cultural practices 24 Human Activities  Site selection and preparation The following types of soil or fields are favorable for the development of epidemics.  Low-lying soil  Poorly drained soil  Poorly aerated field  Field near the infected field 25 Human Activities Selection of propagative materials  Use of infected seeds  Infected nursery stock  Infected rootstock and scion  Diseased suckers  Diseased cuttings 26 Human Activities Cultural Practices Cultural practices that increase the possibility and severity of epidemics, are:  Continues monoculturing  Higher degree of uniformity  No –till culture  Dense planting 27  Overhead irrigation  Injury by herbicide application  Poor sanitation Time Factors 1. Season of the year 2. Duration & frequency of favorable temperature and rains 3. Appearance of vectors 28 Measurement of plant disease & yield loss 1. Disease incidence  Number of plants units that are diseased in relation to  Total number of units examined  Commonly used to measure the spread of a disease 29 FORMS OF EPIDEMIC Based on occurence, mode of spread and severity of infection, the epidemic may be defined in various ways: Local - epidemic occurs in a particular area. Regional - occurs over a wide areas or regions. Endemic - an epidemic which has established in 30 a particular area for a long term and more or less appears constantly from year to year. FORMS OF EPIDEMIC Based on occurrence, mode of spread and severity of infection, the epidemic may be defined in various ways: 4. Pandemic - when an epidemic occurs over most of a continent and causes mass mortality: e.g. late blight of potato caused by Phytophthora 31 infestans (Irish famine of 1845) FORMS OF EPIDEMIC Based on occurence, mode of spread and severity of infection, the epidemic may be defined in various ways: 5. Sporadic - an epidemic that occurs over a large area with irregular intervals and location, and in relatively fewer populations. 32 6. Cyclic - an epidemic which appears periodically after certain intervals of time in a particular area. 04 FACTORS FAVORING THE DEVELOPMENT OF EPIPHYTOTICS c et ce To an tal nd , a EN EN o bu fc c e OG V IR on eas len TH ON di s dit The Disease iru PA ME i on Triangle DISEAS N sf T e 33 fv E av lo o ri ta ng To Total of conditions favoring susceptibility HOST DMMMSU-CAFF DIAGNOSIS OF TREE DISEASES 34 Reymark P. Rivera, RPF Faculty, CAFF Tree Diagnosis art of recognize a disease from its symptom. it is a visual inspection of the foliage, trunk and stems of the symptomatic tree for evidence of disease. 35 06 Importance of Tree Disease Diagnosis To provide treatment. To start timely management and minimize losses. Improve the effectiveness of treatment and avoid long-term complications of the infected trees. 36 To prevent or stop outbreak. Create database of insecticides for respective and disease. 06 When making a tree or plant diagnosis: Accurately identify the plant Look for a pattern of abnormality Carefully examine the landscape Examine the roots Check the trunk and branches Note the position and appearance of affected 37 leaves. 06 Principles of Plant Disease Management Avoidance Exclusion Eradication Protection Resistant varieties Therapy 38 06 Principles of Plant Disease Management Avoidance - avoiding disease by altering planting time, or planting in areas where inoculum is ineffective due to environmental conditoon or rare or absent. Exclusion - preventing the inoculum from entering 39 or establishing in the field or area where it does not exist. 06 Principles of Plant Disease Management Eradication - aims at elimimating a pathogen after it is introduced into an area before it has become well established or widely spread. Eradication can be done by: Destroying weeds that are reservoirs of various pathogens or insect vectors of disease. 40 Biological control of plant pathogen. Crop rotation Soil treatment 06 heat and chemical treatment Principles of Plant Disease Management Protection - preventing infectiob by creating a checmical toxic barrier between the plant surface and pathogens. Chemical treatment Chemical control of insect vector Modification of environment or environment 41 condition Modification of host nutrition 06