Lesson Notes By Weeks and Term v4 - SHS 2
HEALTH ISSUES IN CROP PRODUCTION
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HEALTH ISSUES IN CROP PRODUCTION
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Agriculture
Class: SHS 2
Term: 2nd Term
Week: 6
Grade code: 2.4.1.LI.2
Strand code: 4
Sub-strand code: 1
Content standard code: 2.4.1.CS.1
Indicator code: 2.4.1.LI.2
Theme: AGRICULTURE AND HEALTH
Subtheme: HEALTH ISSUES IN CROP PRODUCTION
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This lesson introduces the critical concepts of crop pests and diseases, which are major challenges to farming in Ghana. Every year, our hardworking farmers lose a significant portion of their harvest to these problems, affecting their income, our food supply (e.g., the price of maize or tomatoes in the market), and the nation's economy (e.g., cocoa exports). By understanding how to classify pests and diseases, we take the first step towards identifying them correctly and managing them effectively. This knowledge is not just for future farmers but for anyone who wants to understand our food systems, run a backyard garden, or contribute to Ghana's food security.
A. Fundamental Definitions Crop Pest: A crop pest is any organism (usually an animal) that causes physical damage or economic harm to crops. Pests can be insects, mites, nematodes, rodents (like rats), or even birds. They harm plants by eating them, sucking their sap, boring into them, or transmitting diseases. *Simple Analogy:* Think of a pest as a thief that comes to steal the plant's food and damage its 'body'. Crop Disease: A crop disease is a condition where the normal functioning of a plant is disrupted by a pathogenic organism (like a fungus, bacterium, or virus) or an environmental factor. This leads to the development of symptoms. *Simple Analogy:* Think of a disease as an illness that makes the plant sick from the inside, showing symptoms on the outside, just like a person with malaria shows fever. B. Classification of Crop Pests
We can classify pests in several ways, but a very practical method for farmers is by their feeding habits, which is determined by their mouthparts. Classification Based on Feeding Habits (Mouthparts) Biting and Chewing Pests: Description: These pests have strong mouthparts (mandibles) that they use to bite, tear, and chew plant tissues. Damage Caused: You will see holes in leaves, skeletonized leaves (only veins are left), eaten-away edges of leaves, bored fruits, or cut stems at the base. Ghanaian Examples: Grasshoppers & Locusts: Eat the leaves of maize, rice, and vegetables. Armyworms: Caterpillars that destroy large fields of maize overnight. Yam Beetle (`Heteroligus meles`): Bores large, ugly holes in yam tubers, reducing their market value. Cabbage Looper: A caterpillar that eats large, irregular holes in cabbage leaves. Piercing and Sucking Pests: Description: These pests have sharp, needle-like mouthparts (a proboscis or stylet) which they use to pierce the plant's skin (epidermis) and suck out the nutrient-rich sap from the phloem. Damage Caused: Their damage is often less obvious initially. It includes yellowing of leaves (chlorosis), stunted growth, wilting, leaf curling, and the presence of a sticky substance called "honeydew," which can lead to a black fungus called sooty mould. Crucially, many are vectors that transmit viral diseases. Ghanaian Examples: Aphids: Small, soft-bodied insects found on the underside of leaves of crops like cowpea and garden eggs. Cocoa Capsids (Mirids): A major pest of cocoa. They suck sap from young pods and shoots, causing black spots and die-back ("capsid blast"). Whiteflies: Tiny white insects that attack tomato and cassava, transmitting devastating viral diseases like Tomato Yellow Leaf Curl Virus and Cassava Mosaic Disease. Mealybugs: Attack cassava, citrus, and pineapple, causing stunted growth. Boring Pests (Borers): Description: These are typically the larval (caterpillar) stage of moths or beetles. They bore or tunnel into stems, fruits, seeds, or roots. Damage Caused: Tunnels inside plant parts, entry/exit holes, wilting of the plant part above the boring point, and internal rotting of fruits. The damage is often hidden until it is too late. Ghanaian Examples: Maize Stem Borer: The larva tunnels into the maize stem, causing the central shoot to die ("deadheart") and the stem to break easily. Bean Weevil: The larva bores into and destroys stored cowpea seeds. Fruit Borers: Caterpillars that tunnel into tomatoes or garden eggs, causing them to rot. C. Classification of Crop Diseases
The most scientific way to classify diseases is by the type of pathogen that causes them. Classification Based on Causative Agent (Pathogen) Fungal Diseases: Description: Caused by fungi. This is the most common group of plant diseases. Fungi reproduce by spores, which can be spread by wind, water, or contact. Common Symptoms: Leaf spots, blights (rapid browning/death of tissue), rusts (orange/brown powdery spots), smuts (black, dusty masses, especially on grains), rots (decay of fruits, stems, or roots), and wilting. Ghanaian Examples: Cocoa Black Pod Disease (`Phytophthora palmivora`): Causes black, rotting patches on cocoa pods, leading to huge yield losses. Maize Rust: Appears as small, reddish-brown pustules on maize leaves. Yam Rot: Fungi like `Aspergillus niger` cause yams to rot in storage. Bacterial Diseases: Description: Caused by single-celled organisms called bacteria. They often enter the plant through natural openings (like stomata) or wounds. Common Symptoms: Leaf spots (often with a yellow halo), wilts (by blocking water-conducting vessels), soft rots (causing tissues to become mushy and smelly), and cankers. Ghanaian Examples: Bacterial Wilt of Tomato: The entire tomato plant suddenly wilts and dies, even with enough water. Citrus Canker: Causes raised, corky lesions on citrus leaves, stems, and fruits. Viral Diseases: Description: Caused by viruses, which are tiny infectious agents that can only replicate inside the living cells of other organisms. They are systemic, meaning they spread throughout the entire plant. They are usually transmitted by vectors (like aphids and whiteflies). Common Symptoms: Mosaic (patches of light green/yellow on leaves), mottling (blotchy patterns), leaf curling, yellowing, and severe stunting of the plant. Ghanaian Examples: Cassava Mosaic Disease (CMD): Transmitted by the whitefly. Causes distorted, yellow-patched leaves and reduces tuber yield drastically. A major threat to gari and fufu production. Maize Streak Virus (MSV): Transmitted by leafhoppers. Causes long, broken yellow streaks along the veins of maize leaves. Tomato Yellow Leaf Curl Virus (TYLCV): Transmitted by whiteflies. Stunts tomato plants and causes leaves to become yellow and curled upwards. Nematode Diseases: Description: Caused by microscopic roundworms called nematodes that live in the soil and attack plant roots. Common Symptoms: Galls or knots on roots (root-knot nematodes), stunted growth, yellowing, and wilting, as the plant cannot absorb water and nutrients properly. Ghanaian Examples: Root-knot Nematodes: Attack the roots of many vegetables like tomato, okro, and garden eggs, causing swollen, lumpy roots. D. Classification of Diseases by Mode of Transmission
This explains *how* the disease spreads. Soil-borne: The pathogen lives in the soil and infects the plant through the roots (e.g., Bacterial Wilt). Air-borne: Pathogen spores are carried by the wind (e.g., Maize Rust). Water-borne: Pathogen is spread through splashing rain or irrigation water (e.g., Black Pod spores splashing from soil to pods). Seed-borne: The pathogen is carried inside or on the surface of seeds (e.g., some bean viruses). Vector-borne: An insect or other pest carries the pathogen from a sick plant to a healthy one (e.g., Whitefly transmitting Cassava Mosaic Virus). Guided Practice (With Solutions)