Practical 13 & 14: Control Measure of Plant Disease

INTRODUCTION

In general, a plant becomes diseased when it is continuously disturbed by some causal agent that results in an abnormal physiological process that disrupts the plant’s normal structure, growth, function, or other activities. This interference with one or more of a plant’s essential physiological or biochemical systems elicits characteristic pathological conditions or symptoms.

Plant diseases can be broadly classified according to the nature of their primary causal agent, either infectious or noninfectious. Infectious plant diseases are caused by a pathogenic organism such as a fungus, bacterium, mycoplasma, virus, viroid, nematode, or parasitic flowering plant. An infectious agent is capable of reproducing within or on its host and spreading from one susceptible host to another. Noninfectious plant diseases are caused by unfavourable growing conditions, including extremes of temperature, disadvantageous relationships between moisture and oxygen, toxic substances in the soil or atmosphere, and an excess or deficiency of an essential mineral. Because noninfectious causal agents are not organisms capable of reproducing within a host, they are not transmissible.

There are six main methods to control plant diseases :

1. Regulatory and quarantine

Plant quarantine regulations are promulgated by the national and the state governments to prevent the introduction and spread of harmful pests and pathogens. Plant quarantine will be justified only when the pest has no natural means of spread and when they are based on biological considerations only, for example pest or pathogen introduction risks and the available safeguards. In general, risks are more with the introduction of vegetative propagules than with true seed. In case of true seed, risks are more with deep-seated infections than with the surface borne contamination of pests or pathogens. Again, risks are far greater with pathogens like viruses, downy mildews, smuts and many bacteria carried inside the seed without any external symptoms. When vegetative propagules are introduced, rooted plants, and other underground plant parts like rhizomes, suckers, runners, etc. carry higher risks than budwood, scions and unrooted cuttings. In any case, bulk introductions are always risky as thorough examination and treatment in such cases is very difficult and planting area is far too large to prevent the establishment and spread of the introduced pest or disease.

2. Cultural control

Cultural control is usually associated with farming systems, although some elements are relevant to landscape and bushcare practices. It largely involves manipulating farming practices to suppress weed growth and production, while promoting the development of the desired plant. The principles and techniques used to prevent weed spread are relevant to cultural control methods to limit the spread of weeds between different land areas.

3. Physical control

From hand pulling, to soil solarization, to benthic barriers, each physical method requires different application tactics and has advantages and disadvantages. In general, controlling invasive plant populations successfully with physical methods depends on selecting a physical method that is compatible with the target species and the management area, and applying the method at the optimal time and intensity to achieve desired outcomes.

4. Biological control

Biological control or biocontrol is a method of controlling pests such as insects, mites, weeds and plant diseases using other organisms.

5.   Chemical control

 Study exhibit on pesticides used to control plant diseases :

1. Fungicides

2. Nematicide

3. Antibiotic/ Bactericides

6. Resistant varieties

Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Relative to a susceptible plant, disease resistance is the reduction of pathogen growth on or in the plant, while the term disease tolerance describes plants that exhibit little disease damage despite substantial pathogen levels.

OUTCOMES

Based on this practise, we can differentiate the function of fungicide, nematicide and bactericide. To control plant disease, there are six methods that can be applied based on types of disease that attack the hosts.