Here is an elaborated discussion on integrated disease management, highlighting:- 1. Meaning of Integrated Disease Management 2. IDM Progress 3. Central Idea 4. Phases 5. Strategies Adopted 6. Integrated Management of Diseases in Crop Harvest 7. Decision Support Systems.
Contents:
- Meaning of Integrated Disease Management
- Progress of IDM
- Central Idea of IDM
- Phases of IDM
- Strategies Adopted for IDM
- Integrated Management of Diseases in Crop Harvest
- Decision Support Systems of IDM
1. Meaning of Integrated Disease Management:
Plant diseases cause enormous economic losses, both quantitatively and qualitatively. According to, conservative estimate, pre- and post-harvest diseases result in more than 30% losses in the developing countries. Consequently, man has developed variety of control devices to combat plant diseases so that he can obtain increased quantity and improved quality of plant products.
But, protecting the crops from diseases is encountering many problems, such as emergence of new virulent strains of pathogens causing dramatic failure in chemical application, environmental hazards, etc. These problems mainly result in due to a ‘quick fix’ mentality in which there is continuous and indiscriminate application of fungicides, and the ignorance of cultural and biological means.
Moreover, the complete destruction of pathogens under field conditions within a growing season using different control devices separately is not only impossible but also economically impractical. One has to repeat the control operation in each crop season to ward off the disease.
What is required is a more lasting solution, using a combination of different disease management strategies, with overall aim to develop sustainable systems of disease management based on a sound understanding of the whole crop ecosystem.
This approach is called integrated disease management (IDM), which, as is considered, will not only maintain the efficacy of host resistance and agrochemicals, but also bring other benefits such as reduced environmental impacts, and lower control costs.
2. Progress of IDM:
Much of the early progress towards an integrated approach was made by entomologists attempting to manage insects’ pests. The concept arose largely from problems with insecticides, including the rapid development of resistance, and a growing awareness of the environmental hazards associated with their use. Also, it was realized that chemicals used to control pests often affected non-target species, including natural enemies of the pest.
However, there was less emphasis until recently on integrated disease management to control plant pathogens for a number of reasons. Initially, at least, there were fewer problems with fungicides than with insecticides. Host genetic resistance to pathogens was a relatively successful strategy, albeit short-lived in certain cases.
Also, there were fewer obvious biological options available to control plant pathogens, such as directly acting predators. Current pressures to adopt a more carefully coordinated approach to disease management derive as much from the need to reduce input costs and environmental impacts, as from the short comings of any individual control strategy.
To date, there are comparatively few examples of fully integrated systems, which combine cultural, chemical, biological, and host genetic factors to control plant pathogens. Nevertheless, progress is being made by putting together packages of measures, which offer significant advantages to growers as well as reducing reliance on chemical agents. It is worth mentioning here that the age of blanket treatment of a crop with a single chemical to control specific disease is to a larger extent over.
Chemicals are increasingly viewed as only one element in an integrated disease management system aimed at maximizing output, while reducing inputs. It is of interest that many agro-chemical companies, have now merged with, or bought stakes in, seed companies marketing particular crop cultivars.
This is part of the trend towards offering the grower an integrated control package, including host genetic resistance. Simultaneously, a number of large agro-chemical companies are investing in plant biotechnology, in the expectation that novel approaches to control, for instance, using transgenic crops (genetically engineered novel disease-resistant crops), will provide additional options alongside their portfolio of chemicals.
3. Central Idea of IDM:
Integrated disease management (IDM) aims at prevention or reduction in the incidence or severity of the disease incited by the plant pathogen. Hence the central idea revolves around the tactical management of the host, the pathogen, and the environment (the three factors of a disease triangle) so as to keep the damage or loss below the economic threshold level.
The strategy utilizes host-plant resistance together with other possible tactics in harmony with the natural regulatory factors of the ecosystem to keep the disease inciting pathogens below the economic threshold level.
Management of the host involves the practices directed to improve plant vigour and host resistance through nutrition, induction of genetic resistance through conventional plant breeding and through genetic engineering, and providing protection against attack by chemical means.
Management of the pathogen involves avoiding contact between the pathogen and the host, eradication, and protective application of chemicals to prevent infection. Management of the environment involves water management, soil management, and crop management.
Criteria of Priority:
The Food and Agriculture Organization of the United Nations has been interested in developing integrated pest/disease management since 1963 and has developed and implemented several field projects in different parts of the world. This organization recommended for global programme to be undertaken on the basis of programme priority. Criteria of programme priority have been ascertained that point out the necessity of IPM/IDM.
These criteria are the following:
1. Crop must be of vital national and regional importance.
2. Serious losses are caused by pests/pathogens.
3. Inadequate control by use of organic pesticides.
4. Use of pesticide is generating more problems, but the same cannot be given up otherwise food production will not be stepped up.
5. An integrated approach can be developed, which will yield desirable results and be acceptable to growers.
Emphasis has been laid on major crops namely, rice, maize, sorghum, cotton, etc. Potato, sugarcane, grain legumes, tapioca, coconut, etc., have also been considered as second order of priority.
4. Phases of IDM:
Integrated disease management is a system approach and consists of following important phases, which significantly contribute in the development of a complete IDM system.
They are:
i. Single Tactic Phase:
In the initial stage, the best method for tackling or managing a disease is found out.
ii. Multiple Tactic Phase:
In this phase, all the available methods — cultural, biological, chemical, and use of resistant varieties are worked out in relation to ecology, inoculum density, and damages. This phase is the most critical one and needs careful work out.
iii. Biological Monitoring Phase:
After the multiple tactics have been decided, they are to be carefully monitored, particularly biological ones, in relation to beneficial organisms and host plants so that management measures may be suitably timed and phased out.
iv. Modeling Phase:
Data obtained from phases 1, 2, and 3 require to be very carefully worked out so that a model can be developed pointing out the major steps that need to be taken regarding the application of management measures and the critical stages in the host plant. The entire approach has to be systematized through critical analysis of data.
v. Management Phase:
After the different models of disease management have been worked out in an integrated manner, the entire process has to be incorporated into the overall production techniques of the crop concerned.
vi. Acceptance Phase:
The most critical stage is the development of system approach acceptable to growers. The approach has to be technologically sound, economically viable, and not too cumbersome for adaptation by growers.
5. Strategies Adopted for IDM:
Integrated disease management (IDM) systems are being developed with their main goals to:
(1) Eliminate or reduce the initial inoculum,
(2) Reduce the effectiveness of initial inoculum,
(3) Increase the resistance of the host,
(4) Delay the onset of disease, and
(5) Slow the secondary cycles of the disease.
These systems therefore combine cultural, chemical, biological, and host genetic factors to combat plant diseases. Nevertheless, progress is being made by putting together packages of measures, which offer significant advantages to growers as well as reducing reliance on chemical agents.
1. Growers are advised to grow healthy, certified, and treated seeds. They should periodically remove and monitor diseased seedlings so that initial inoculum could be checked without further spread in main field.
2. Crop rotation of cereals, paddy, sugarcane, and coarse millets with vegetable crops substantially reduces the soil-borne disease.
3. Crop residues, rotted fruits, infected plant parts, and weeds should be periodically removed. This reduces pathogen perpetuation and also pathogen inoculum.
4. In vegetable crops, sowing time and transplanting pattern particularly ridge sowing reduces water stagnation, root rot, and wilt incidence. Plant spacing should be adjusted keeping plant canopy in view to avoid easy disease spread in dense crop.
5. Disinfection of agricultural implements, tools, plant support materials are advised particularly for viral disease management.
6. Lower, older, and senescent leaves should be removed. This reduces infection site by various facultative pathogens.
7. Maximum use of organic supplement, alternate year green manuring for augmentation of antagonistic microbial population, and biological control.
8. Integration of fungicides with host resistance, and integration of cultural and biological measures should be followed.
9. There should be strict legislation for pesticide dealers so that they do not sale spurious chemicals and cannot misguide the growers by giving so many pesticide, growth regulators, etc. for use at a time without its real need.
10. The use of trap crop, border/barrier crop, disease escape varieties, etc. proves to be effective in reduction of disease.
11. In vegetables, allelopathic crop, which produces toxic root exudates for pathogen, must be encountered.
12. Postharvest practices should be used to avoid any rotting and seed infection during storage and transportation.
13. Growers should be essentially trained for correct diagnosis of the disease to apply different measures of integrated disease management at critical period.
6. Integrated Management of Diseases in Crop Harvest:
Integrated Management of Diseases in an Annual Crop:
A single annual crop may be attacked by many diseases in a growing season but all such diseases may not occur simultaneously or concurrently in a particular locality. The possibility of occurrence of any one or more of them in the field during the growing season does exist. An integrated management programme of an annual crop, such as potato crop, is taken here for instance.
In Indian subcontinent and elsewhere, late and early blight diseases, black scurf/stem canker, bacterial wilt and brown rot, root knot, and mosaic and leaf curl are quite common diseases of this crop. Due to nature of propagation of the crop all the diseases are mainly seed (tuber) borne. Some of them are soil-borne also. Spread by soil, insects, water, and wind is common.
Therefore, in this crop the improvement of quality and quantity of the yield through disease control can be brought about by adopting a schedule prepared on the following lines:
The first step is the proper selection of the field for potato. Fields in which there has been serious incidence of soil-borne diseases of potato during last some growing seasons should be avoided. Also, the selected field must have proper drainage and high level of fertility.
The second step in the selection of resistant varieties for those areas where late blight regularly occurs every year even if they do not yield as much as a susceptible but high yielding variety.
The third step in the selection of seed. Potato tuber seed may carry variety of pathogens (e.g., several viruses, bacteria, fungi, nematodes) on or within it and may introduce the pathogen in the field. Therefore, use of clean and disease-free seed is of paramount importance. Such seeds should be obtained from sources, which guarantee seed- certification.
Certified seed is usually produced under strict quarantine and inspection rules that guarantee seed free of pathogens. In absence of such an arrangement, seed tubers can be obtained from a field where necessary steps for management of diseases (rouging, spraying, etc.) have been taken and tubers for seed have not been collected from diseased plants.
The fourth step is the additional precautions in the form of chemical treatment of seeds. Additional precautions should be taken by treating the seed tubers with fungicides such as Areton, Agallol, Benlet, etc., which helps eradicating residual inoculum and protects it during germination and emergence.
The fifth step is the date of planting. The latter should be decided according to prevailing soil temperature and moisture. High soil temperature and moisture should be avoided.
The sixth step is the protection of plants from infection. A few weeks after young plants have emerged, under conditions of stress or high moisture, they become susceptible to attack by early blight (Alternaria solani) or late blight (Phytophthora infestans). If these diseases occur regularly year after year in that area, the grower should start spraying with fungicides such as Zineb, Mancozeb, Copper oxychloride, etc.
Other fungicides such as Dithane Z-78, Dithane M-45, Lonacol, Difoltan, Blitox-50, etc. should be sprayed in normal conditions when the crop is about 6 inch high and the sprayings be repeated at 10-12 day intervals depending upon occurrence of the foliar diseases in the neighbourhood and upon weather.
The seventh step is the destruction of infected plant debris before harvesting. Infected plant debris must be destroyed before harvesting so that the pathogen inoculum could not come in contact with the tubers when they are dug up.
The eighth step is to protect tubers from being wounded. Tubers must be harvested carefully to avoid wounding that would allow storage-rot fungi such as Fusarium and Pythium, and bacteria such as Erwinia carotovora, to gain entrance into the tuber. Wounded tubers, if any, must be sorted out and discorded.
The ninth step is the proper storage. Healthy tubers should be stored at about 15°C for healing of wounds and then at about 10°C to prevent development of fungus rot in storage.
Integrated Management of Diseases in a Perennial Crop:
In an integrated disease management programme of an orchard crop like apple, peach, citrus, etc., one must first consider the nursery stock to be used and location where the saplings will be planted.
In case the trees of the concerned orchard are known to be susceptible to viruses, phytoplasmas (= MLOs), crown-gall bacterium, or nematodes, the nursery stock (both the root- stock and scion) must be free from these agents. Even after obtaining the saplings from a nursery where they were scientifically inspected and certified, the stock must be appropriately treated with fumigants, especially to eliminate nematodes.
The next step is selection of appropriate planting sites. Variety of pathogens, e.g., Armillaria, Fusarium, Phytophthora, etc., and several nematodes are known to survive in soil. If the experience and history suggest their presence in selected soil, the soil should be treated with suitable pesticide, particularly with fumigants before planting.
As far as possible, rootstock resistant to these pathogens should be preferred. The drainage of the location should be checked and improved, if necessary. Finally, the young trees should be avoided from being planted between or next to heavily infected old trees with canker fungi and bacteria, insect-transmitted viruses and MLO, pollen transmitted viruses, or with other pathogens.
Once the trees have established and until they begin to bear fruits, they should be fertilized, irrigated, pruned, and sprayed for the most common insects and diseases. As a result, they will grow vigorously and remain free of infections. Any tree that develops symptoms of a disease caused by a systemic pathogen should be removed and destroyed at the earliest. Later on when trees bear fruits, the utmost care should be taken to control diseases that affect them.
The following step-wise treatments ensure healthy crop of fruits if carefully employed:
i. Removal through pruning and destruction of dead twigs, branches, and fruits. This ensures reduced amount of initial inoculum of the pathogens that initiate infection.
ii. Pruning shears and saws should be disinfected before moving to new trees so that the spread of the inoculum should be avoided.
iii. A dormant spray containing a fungicide-bactericide (e.g., Bordeaux mixture) or a plain fungicide plus a acaricide-insecticide (e.g., Superior oil), should be applied before bud break.
iv. After the buds open, blossoms and leaves must be protected with fungicide and/or a bactericide sprays and, possibly, an insecticide and/or acaricide that does not harm bees.
v. Young fruits appear when blossoming is over. If the young fruits are infected, appropriate chemical sprays should be undertaken.
vi. Usually the fruits become susceptible to several fruit-rotting fungi at early maturity through harvest and storage. Therefore, fruits must be sprayed at 15 day intervals with chemicals that will control these pathogens till harvest. Most fruit rots begin at wounds made by insects, and, therefore, insect control must continue.
vii. Also, wounding of fruits during harvesting and handling must be avoided so that any fungus infection should be avoided.
viii. Harvested fruits should be washed in a water solution containing a fungicide to further protect the fruits during storage and transit. During packing, infected fruits must be sorted out and discarded.
7. Decision Support Systems of IDM:
If a farmer wants reduced or no loss of his crop from diseases, he has to take decisions such as which variety to sow, and when or whether to apply agrochemicals or some other control measure. His decision should be accurate because accuracy of decision is an important aspect of integrated disease management. Although the decision may be usually simple in case of a destructive disease outbreak (e.g., late blight of potato), but it may not be simple in case of many diseases the critical factors of which may not be obvious.
There is, therefore, always a need for additional informations on which to base a decision followed with a course of action. The additional informations can only be provided by decision support systems to help farmers to make the correct choices for integrated disease management. Such support systems derive from long established principles of disease forecasting, but differ in the scale and complexity of data they can handle, and the active participation of farmer in decision making process.
A typical decision support system consists of certain basic components. While each support system varies in its design and purpose, most combine information from databases with simulation models and expert systems. The key resource of a support system is usually a database that holds very large sets of information regarding incidence patterns of a disease in the past, and its responses to then applied chemical treatments.
The simulation models calculate particular processes (e.g., epidemic development or the multiplication of disease vectors) taking the help of existing data and any new information input by the user.
As such estimates integrate many factors and handle large amounts of data, they require the speed and power of modern computers to function effectively. The expert system functions as an interactive interface which requests information from the user, and then provides estimates of disease risk as well as suitable options for disease management.
Most decision support systems, at present, are based on incomplete databases and relatively simple model systems, and are at an experimental stage. Such systems are under constant refinements to improve the accuracy of disease risk estimates, and also to provide more precise, site-specific recommendations that take local climatic variations, topography, soil, etc. into account. Nevertheless, the decision support systems are being used in USA and Europe.
Fig. 19.2 shows the relative need for fungicide treatments to control three foliar diseases of wheat in Denmark during 1991 and 1992 seasons. It was found during 1991 season that there was little need for control of yellow stripe rust, a fairly constant risk of mildew, and a high risk of Septoria. The story was changed during 1992 season. In this season, there was estimated little risk of damage from any of these diseases, and the application of fungicides would have been a waste investment.
No comments yet.