There are mainly six (6) principles of plant disease management that protect crops from both quality and quantity losses. So in this article, we will explore the basic 6 principles of plant disease management.
The goal of plant disease management is to reduce the economic and aesthetic damage caused by plant diseases. Plant disease management practices rely on anticipating the occurrence of disease and attacking vulnerable points in the disease cycle. Therefore, a correct diagnosis of a disease is necessary to identify the pathogen, which is the real target of any disease management program.
Plant diseases are considered an important biotic constraint of crop production, which leads to significant crop losses throughout the world both quantitatively and qualitatively. The list of pathogens harmful to crops is large and extremely diverse.
Principles of plant disease management:
There are many principles of plant disease management described as given below:
1. Avoidance of pathogen
2. Exclusion of pathogen
3. Eradication of pathogen
4. Protection of crop
5. Disease resistance in the host
6. Therapy of host plants
1. Avoidance of pathogen
This is a principles of plant disease management where effort is made to avoid the pathogen by growing the crops when inoculum is rarely absent or ineffective due to unfavorable environmental conditions. Avoidance of the pathogen can be achieved by
(1) Choice of geographic area
(ii) Proper selection of field
(iii) Adjusting the time of sowing
(iv) Growing disease-escaping varieties
(v) Selection of seed and planting stock
(vi) Modification of cultural practices
(i) Choice of geographic area:
The main idea in the choice of geographical area is to grow crops in areas where the environmental condition is unfavorable for the pathogen and favorable for the crop. Many fungal and bacterial diseases are more severe in wet areas than in dry areas.
For example, smut (Tolyposporium penicillariae) and ergot (Claviceps microcephala) of finger millet are more serious in wet conditions. Thus growing finger millet in dry areas with irrigation facilities is helpful to avoid diseases.
(ii) Proper selection of field:
Some diseases such as many soil-borne diseases become more serious year after year if the same crop is grown continuously due to the build-up of more inoculums. In such conditions, the selection of fields is more important to grow the crop. If such fields are cultivated with some other non-host crop (crop rotation) of the pathogen the disease can be avoided.
The Red rot disease of sugarcane (Colltotrichum falcatum), Bacterial wilt disease of solanaceous crops (Ralstonia solanecearum), Root-knot nematode (Meloidogyne spp) ete can be reduced by changing the field of cultivation.
(iii) Adjusting time of sowing:
In this coincidence, the susceptible stage of crop and environment favorable for the pathogen is avoided and disease incidence is reduced. Alteration of the date of sowing can help in the avoidance of favorable conditions for pathogens.
For example, Rhizoctonia root rot of red gram is more severe in the crop sown immediately after the rains. Delayed sowing will help in reducing the incidence of disease. Again, stem rust of wheat (Puccinia graminis tritici) is more severe in late sown crops. Therefore, early sowing of wheat helps in reducing the stem rust incidence.
(iv) Growing disease-escaping varieties:
Certain varieties of crops escape disease damage because of their growth characteristics. The disease-escaping qualities of the varieties are due to characteristics of growth and time of maturity. Early maturing varieties of wheat or pea escape the damage due to black rust (Puccinia graminis tritici) and Powdery mildew (Erysiphe polygoni) respectively. So, the growers can effectively utilize these varieties to minimize the disease incidence.
(v) Selection of seed and planting stock:
Most of the pathogens can be carried in or on the seed and planting materials. Pathogen-causing bean anthracnose(Colletotrichum lindemuthianum), and bacterial blight of beans (Xanthomonas phaseoli and Pseudomonas phaseolicola) are transmitted by seed.
Diseases like the bunchy top of banana (Banana Bunchy Top Virus), Citrus tristeza disease (Citrus Tristiza Virus), Panama wilt of banana (Fusarinen oxysporum f.sp. cubense) etc are carried with the planting materials. Therefore, seed and planting materials free from pathogen infection must be obtained from disease-free areas to reduce the disease incidence.
(vi) Modification of cultural practices:
Modification of cultural practices like changes in time and area of planting, plant density, amount and type of fertilizers, cropping pattern (mixed crop, trap crop, intercrop), change in variety, etc. plays an important role in avoiding the incidence of plant diseases.
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2. Exclusion of pathogen
In this principle, attempts are made to prevent the inoculum from entering or establishing in the field or area where it does not exist. The basic strategy assumes that most pathogens can travel only short distances without the aid of some other agent such as humans or other vectors.
Different methods of exclusion are:
(1) Seed treatment
(ii) Inspection and certification
(iii) Quarantine
(iv) Control of insect vectors
(i) Seed treatment:
Treating seeds before planting is very effective in removing the pathogen inoculums that may be carried externally or internally in the seed. This practice also helps in preventing the entry of a new pathogen from entering an area where that does not exist.
(ii) Inspection and Certification:
This is an important and practical strategy for excluding pathogens by producing pathogen-free seed or planting stock through certification programs for seeds and vegetatively propagated plant materials such as potatoes, grapes, tree fruits, etc. These programs utilize technologies that include isolation of production areas, and field inspections. and removal of suspect plants to produce and maintain pathogen-free stocks.
(iii) Quarantine:
Plant quarantine is the legal restriction on the movement of agricultural commodities for exclusion, preventing, or delaying the spread of plant pests and diseases in uninfected areas. When new pathogens are introduced in an area in which they did not exist previously, may cause much more damage than do the previously existing pathogens. Keeping this in view, to keep foreign plant pathogens out of the farms to protect the crops, the Plant Quarantine Act was enacted in the USA in 1912.
Much before that, Plant quarantine laws were first enacted in France in 1660. Similar to the USA, the Destructive Insect Pest Act was enacted in India in the year 1914.
Under this act, various quarantine stations are established in the major entry points like land frontier, seaports, and airports. Seed and planting materials immediately after their arrival, scientific staff engaged in these quarantine stations follow various steps like inspection of the materials, growing of plants under observation for a certain period, etc. Before they are released to the importers no unwanted foreign pathogens enter to the country. Likewise, within a country, there is Domestic Quarantine which is the legal restriction of movements of seed and planting materials from one state where a pathogen has prevailed in endemic form to another state where it is absent.
In India, the movement of potato tubers from the Darjeeling areas of West Bengal to other states is restricted to prevent the spread of wart disease of potatoes. Likewise, the movement of banana suckers from Kerala, Assam, Bihar, West Bengal, and Orissa is restricted to prevent the spread of Banana Bunchy Top Virus (BBTV) to other states of India.
(iv) Control of insect vectors:
Vectors are the transmitters of disease-causing organisms; that is, they carry pathogens from one host to another. Vector-borne plant diseases, including several newly recognized pathogens, reduce agricultural productivity and disrupt ecosystems throughout the world.
Among the different types of plant disease vectors, the insects carry more than 80 percent of the plant virus diseases. Therefore, insect vector-borne plant disease can be effectively managed by controlling the insect vectors. The insect vectors can be controlled by different methods, like cultural control, and physical and mechanical control. Pheromone traps, biological control, and chemical control.
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3. Eradication of Plant Pathogens
This plant disease management principle aims at eliminating a pathogen after it has been introduced into an area but before it has become well-established or widely spread. This is accomplished by taking various measures like- crop sanitation, summer plowing, Removal of alternate and collateral hosts, Soil fumigation, rouging of infected plants, crop rotation, etc.
4. Protection of crop
This principles of plant disease management where infection is prevented by creating a chemical toxic barrier between the plant and the pathogen. This is achieved by
(i) Chemical treatment:
Fungicides, bactericides (antibiotics), and nematicides have been used in the crop production system to protect the plants from infection by fungi, bacteria, and nematodes respectively. Fungicides have been used for more than a hundred years and new fungicides continue to be developed.
Earlier Bordeaux mixture was the extensively used fungicides which are followed by sulphur fungicides. The development and use of organic fungicides such as thiram, captan, and the bisdithiocarbamates as broad-spectrum, contact, or protectant fungicides resulted in the control of a wide range of fungal diseases. The systemic fungicides finally gave the highest opportunity to control infectious pathogens
(ii) Control of insect vectors:
Effort is made to reduce or minimize the spread the insect-borne diseases by controlling the insect vectors. The insect vectors can be controlled by different methods like physical or mechanical means, biological control by releasing predators and pathogens, biopesticides, pheromone traps, and by applying chemical insecticides
(iii) Modification of growing environments:
This is a strategy for disease management that often involves alteration/modification of some of the cultural practices such as tillage. drainage, irrigation, or altering soil pH, etc. that lead to the modification of the crop environment.
It may also involve alteration of plant spacing, changing the date of sowing/planting, pruning, and thinning, or other practices that allow plants to escape infection or reduce the severity of disease Growing crops especially the seedlings in raised beds ensures good aeration and soil water drainage is an important modification of cultural practices which ultimately leads to the modification of crop growing environment for protecting crops from plant diseases such as damping off, root and stem rots.
5. Resistant varieties
In this method, the focus is mainly given to planting disease-resistant varieties. Resistance in the host plant is achieved by altering the genetic system of the host to make it less susceptible to the disease organism. The use of disease-resistant plants eliminates the need for additional efforts to reduce disease losses unless other diseases are additionally present.
There are two types of resistance used in plant disease management. Vertical resistance provides a very high level of resistance, or immunity, to specific strains of disease organisms. Horizontal resistance is a lower level of resistance, or tolerance, to many more strains of disease organisms.
Vertical disease resistance is conferred by a single major gene which is sometimes called specific or qualitative resistance and is race-specific. This type of resistance is often unstable, and the emergence of a pathogenic race that can attack that genotype can completely overcome this type of resistance.
Horizontal resistance quantitative resistance or general resistance is derived from many different minor genes for resistance which gives additive effects to provide more stable (or durable) resistance to pathogens. Both types of resistance are used in the development of agricultural crop plants.
6. Therapy of the host plant
Therapy is the reducing severity of disease in an infected individual. Generally, heat or chemical treatment is applied to vegetative planting materials such as bulbs, corms, and woody cuttings to eliminate fungi, bacteria, nematodes, or viruses that are established within the planting material.
Chemotherapy is the application of chemicals to an infected or diseased plant that stops (ie., eradicates) the infection. When heat (hot water or hot air treatment) is applied to the planting materials to eradicate the infection it is called heat therapy. The removal of the infected portion/infected stem of the plant to reduce disease incidence is called tree surgery etc, are the principles of plant disease management.
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