Ministry of Education Secondary Engagement Programme November 2020
Ministry of Education Secondary Engagement Programme November 2020 Grade 9 Agricultural Science Week 8 Lesson # 2 Topic: Crop Protection Subtopic: Diseases of plants 1
Diseases of plants • An abnormal condition in the growth and development of a crop plant is called disease. Symptoms of Diseases • • • Discoloration Necrosis Dwarfing of plants or plant parts Swelling of plant parts Dropping of leaves , blossoms or fruits Roughening of fruits or stem surfaces Deformed fruits Complete distortion of some of the plant organs Death of infected plants before maturity 2
Disease causing Organisms 3
Methods of Control • • • Cultural Use of resistant varieties Quarantine Biological Chemical Integrated Pest Management (I P M) 4
Cultural Control • It is the modification of ordinary farm operations to enables the crop to escape pest attack • The methods are in expensive and can be carried out as a part of the routine operation in crop production. • § § § These methods are : Early or late Ploughing or planting Deep Ploughing Field hygiene or farm sanitation Weed removal Crop rotation Resistant variety • Some variety of crop plants pose difficulty to pests and diseases • The prevent the organisms from attacking them • The resistance may be due to inherited characteristics (Genetic or physical ones) • This method has been successful in eliminating the damage caused by some insect pests 5
Quarantine • Most countries have law which permit the importation ad distribution of pest – free plants or plant part only • This aims at preventing the introduction of new pests in to a country or area or preventing the spread of already existing pests to other areas in the country which have been free of the pest • Some of the pests that are prohibited from entering countries are Colorado beetle, fruit flies, grape phylloxera (aphid). Biological Control • This measure utilizes natural enemies of pests, e. g. predators (ladybird beetle, lacewing), parasites(wasps , Amazon fly), and pathogens(some fungi , bacteria and viruses). These natural enemies may be either locally present and need to be increased by creating an environment conducive to their multiplication and spread, or deliberately introduced from countries of their origin and multiplied and released in pest infested areas. • It is a promising method to keep some insects pest population at a low level. It has been successful in the control of many pests introduced into a country unaccompanied by their natural enemies. The larvae of Braconid wasps are used to control pests belonging to the class Lepidoptera (butterflies and moths). 6
• Chemical Control Pests may be killed by exposing them to toxic substances • These chemicals are generally called pesticides. the include insecticides and ascaricides used against insect and mites pests and herbicides (Weedicides) against weeds • The different pesticides may be grouped according to their mode of action. Integrated Pest Management (I P M) • This emphasizes the use of biological, cultural and mechanical methods before chemical control • It involves the best combination of cultural biological mechanical and chemical measures • It yields the most cost –effective, environmentally sound and socially acceptable forms of pest 7
Exercises 1) (a) List three common symptoms of disease attack in plants (b) Name two common plant diseases caused by each of the following 2) List three reasons for discouraging the use of chemicals in the control of diseases 3) State the benefits of the use of quarantine, biological and integrated pest management for the control of crop diseases 8
References • Sahadeo Ragoonanan (2011) ‘Agriculture for CSEC Revision course’ New Edition, Caribbean Educational Publisher Ltd, Trinidad, WI • Fitzroy Weever et al (2014) Agricultural Science for Secondary Schools in Guyana, Book 3, Ministry on Education NCERD, Georgetown, Guyana • Sahadeo Ragoonanan (1991) CXC Agriculture- A Revision Course, Caribbean Educational Publisher Ltd, Trinidad, WI 9
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