Principles of Plant Disease Control

Dr. Sanjeev Kumar

Assistant Professor/Scientist Plant Pathology JNKVV-Jabalpur

[email protected]

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Principles of Plant Disease Control

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Techniques used in disease management mainly based on two principles 1. Prevention or Prophylaxis 2. Cure

1.Prevention or Prophylaxis • Disease management tactics applied before infection. • Plant is protected from disease. • Includes: avoidance, exclusion, eradication, resistant & protection. 2. Cure • Functions with any measure applied after the plant is infected . • Plant is treated for the disease. • Includes therapy

Principles of plant disease control Prophylaxis Avoidance

Curative

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Prevent disease by selecting a time of the year or a site where there is no inoculum or where the environment is not favorable for infection

Exclusion

Prevent the introduction of inoculum

Eradication

Eliminate, destroy or inactivate the inoculum

Protection

Prevent infection by means of a toxicant or some other barrier to infection

Resistance

Utilize cultivars that are resistant to or tolerant of infection Cure plants that are already infected

Therapy

Avoidance of pathogen

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Avoiding disease by planting at times when or where inoculum is absent or ineffective due to unfavorable environment conditions. • Choice of geographic area • Selection of field • Choice of time of sowing • Disease escaping varieties • Selection of seed and planting stock • Modification of cultural practices

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Exclusion of inoculum Preventing the inoculum from entering or establishing in the field or area where it does not exist. 1. Seed treatment 2. Inspection and certification 3. Quarantine 4. Eradication of insect vectors

Eradication of Pathogens

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Reducing, inactivating, eliminating or destroying inoculum at the source, either from a region or from an individual plant in which it is already established. 1. Biological control of plant pathogen 2. Crop rotation 3. Removal or destruction of diseased plant organs 4. Rouging 5. Eradication of alternate and collateral hosts 6. Sanitation 7. Heat and chemical treatment of disease plants 8. Soil treatments

Immunization/Disease resistance

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It involves the modification of certain physical or physiological character(s) of the host such that it can repel infection or can reduce disease development or can minimize damage caused by the pathogen. Methods used are 1. Use of resistant varieties 2. Cross-protection Cross protection refers to the protection of a plant by use of a mild strain of a pathogen against a virulent strain of the same pathogen that can cause more severe symptoms and damage.The method is generally used for viral disease management. Disease resistance: Altering the effectiveness of the pathogen by selection or introduction of resistance genes in the plant. 1. Selection and hybridization for disease resistance 2. Resistance through chemotherapy

Protection measures

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Preventing infection by creating a chemical toxic barrier between the plant and the pathogen is comes under protection measures 1. Chemical treatment 2. Chemical control of insect vectors 3. Modification of environments

Therapy

Reducing severity of disease in an infected individual

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1. Chemotherapy: • Application of chemicals to an infected or diseased plant that stops the infection. • Examples: heat or chemical treatment of vegetative material such as bulbs, corms, and woody cuttings to eliminate fungi, bacteria, nematodes or viruses that are established within the plant material. 2. Heat therapy: • Hot water treatment of rice seed at51-53oC for 15 min after dipping for 1 d in cool water for management of white tip disaesce caused by Aphlenchoides besseyi 3.Tree surgery: 1. Use of chaubatia paste after pruning of diseasesd parts in horticultural crops.

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While these principles are valid today In the context of modern concepts of plant disease management,

they have some critical shortcomings

Critical Shortcomings

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1. Principles of plant disease control are stated in absolute terms like exclude, prevent and eliminate that imply a goal of zero disease. 2. Plant disease control in this sense in not practical, and in most cases is note even possible. 3. Indeed, we need not eliminate a disease; we merely need to reduce progress and keep disease development below an acceptable level. 4. Instead of plant disease control, we need to think in terms of plant disease management. 5. These principles donot take consideration the dynamics of plant disease, that is the changes in the incidence and severity of disease in time and space. 6. We need some means of assessing quantitatively the effects of various control measures, singly and in combination on the progress of disease. 7. Finally, these principles of plant disease control tend to emphasize tactics without fitting them into an adequate overall strategy. Does this mean that we should abandon the traditional principles ? Of course not We merely have to fit them into an appropriate overall strategy

Strategies versus Tactics

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• Dictionary definitions of the two terms are similar. • Strategies : An overall plan for reaching a particular objectives is called strategy, • Tactics: Specific means for implementing a given strategy are called tactics. • What is a strategy at one level of focus could be called a tactic at another level of focus

Strategy of Disease Management

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I. Complete eradication of a pathogen from the earth of the ecosystem is very difficult and against the law of nature. II. Therefore, the strategy for disease management should be to reduce the population of pathogen below permissible level so they do not cause damage. III. Keeping this in mind, the strategy of disease management should integrate all known methods taking into account the following factors. 1. 2. 3. 4. 5.

Pathogen inhibition Tolerable losses Economical control Long term control Collective approach

Strategy of Disease Management (Conti.)

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1. Pathogen inhibition

• As complete eradication of a pathogen is not possible,. • More emphasis should be on to develop a technology which maintain their population below the damaging level. 2.Tolerable losses • Tolerate the level of disease that do not harm economically. • For example, in crops raised for seed two per cent disease infection is permissible, whereas in crops raised for consumption the permissible limit is 5 per cent. 3. Economical control • Strategy for disease management should be implemented after considering the cost benefit ratio.T • Return per unit of money spent must be sufficiently high. 4. Long term control 1. Utilize methods which have a long term effect so as to reduce the expenses and pollution of the environment. 5. Collective approach • Disease control cannot be achieved by a single farmer since pathogen can move from field to field. • Hence, collective area wise approach is necessary for effective control.

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