Agri Pest Contorl
Organic Pest and Disease Management
Prevention practices and monitoring
Plant health and pest and disease ecology helps the farmer to choose effective preventive crop protection measures.
Some important preventive crop protection measures are the following ones:
1) Selection of adapted and resistant varieties:
Choose varieties which are well adapted to the local environmental conditions (temperature, nutrient supply, pests and disease pressure), as it allows them to grow healthy and makes them stronger against infections of pests and diseases.
2) Selection of clean seed and planting material :
- Use safe seeds which have been inspected for pathogens and weeds at all stages of production.
- Use planting material from safe sources.
3) Use of suitable cropping systems
- Mixed cropping systems: can limit pest and disease pressure as the pest has less host plants to feed on and more beneficial insect life in a diverse system.
- Crop rotation: reduces the chances of soil borne diseases and increases soil fertility.
- Green manuring and cover crops: increases the biological activity in the soil and can enhance the presence of beneficial organisms
4) Use of balanced nutrient management :
- Moderate fertilization: steady growth makes a plant less vulnerable to infection. Too much fertilization may result in salt damage to roots, opening the way for secondary infections.
- Balanced potassium supply contributes to the prevention of fungi and bacterial infections
5) Input of organic matter:
- Increases micro-organism density and activity in the soil, thus decreasing population densities of pathogenic and soil borne fungi.
- Stabilises soil structure and thus improves aeration and infiltration of water.
- Supplies substances which strengthen the plant‘s own protection mechanisms.
6) Application of suitable soil cultivation methods:
- Facilitates the decomposition of infected plant parts.
- Regulates weeds which serve as hosts for pests and diseases.
- Protects the micro-organisms which regulate soil borne diseases.
7) Use of good water management:
- No water logging: causes stress to the plant, which encourages pathogens infections.
- Avoid water on the foliage, as water borne disease spread with droplets and fungal disease germinate in water.
8) Conservation and promotion of natural enemies:
- Provide an ideal habitat for natural enemies to grow and reproduce.
- Avoid using products which harm natural enemies.
9) Selection of optimum planting time and spacing:
- Most pests or diseases attack the plant only in a certain life stage; therefore it’s crucial that this vulnerable life stage doesn’t correspond with the period of high pest density and thus that the optimal planting time is chosen.
- Sufficient distance between the plants reduces the spread of a disease.
- Good aeration of the plants allows leaves to dry off faster, which hinders pathogen development and infection.
10) Use of proper sanitation measures:
- Remove infected plant parts (leaves, fruits) from the ground to prevent the disease from spreading.
- Eliminate residues of infected plants after harvesting.
Regular monitoring of pests, diseases and weeds is the basis for effective management.
a) Typical signs of pest attacks on crop plants
Most crop pests belong to the insects, mites and nematodes.
Insect damage can be categorized by biting and chewing (e.g. caterpillars, weevils), piercing and sucking (e.g. aphids, psyllids) and boring (e.g. borer, leaf miner) species. Some are slow moving (e.g. caterpillars), fast moving (e.g. fruit flies), hidden (e.g. stem borer), or easy to observe (e.g. caterpillars, weevils).
Pest damage is often species-specific: leaves with holes or missing parts is an indication of caterpillar or weevil damage; curled leaves is an indication of aphids; damaged or rotten fruits are often caused by larvae of fruit flies; withering plants can also be caused by larvae of noctuids or the stem borer; and branches or trunks with holes may be an attack by lignivorous insects.
Mites are very small and cannot be seen with the naked eye. However, some mite species (spider mites) weave a typical tissue on attacked plant parts and can, therefore, easily be detected. If mites are present on plants, leaves and fruits become yellowish.
Nematodes are also very small and therefore, they are not easy to observe with the naked eye. They mostly attack plant roots; plants become yellow, wither and die.
b) Typical signs of disease attacks on crop plants
Fungi cause the great majority, estimated at two-thirds, of infectious plant diseases. They include all white and true rusts, smuts, needle casts, leaf curls, mildew, sooty moulds and anthracnose. In addition, they are responsible for most leaf, fruit, and flower spots, cankers, blights, wilts, scabs, and root, stem, fruit, wood rots among many others.
Bacteria cause any of the four following main problems. Some bacteria produce enzymes that breakdown the cell walls of plants anywhere in the plant. This causes parts of the plant to start rotting (known as ‘rot’). Some bacteria produce toxins that are generally damaging to plant tissues, usually causing early death of the plant. Others produce large amounts of very sticky sugars; as they travel through the plant, they block the narrow channels preventing water getting from the plant roots up to the shoots and leaves, again causing rapid death of the plant. Finally, other bacteria produce proteins that mimic plant hormones. These lead to overgrowth of plant tissue and form tumours.
Viruses mostly cause systemic diseases. Generally, leaves show chlorosis or change in colour of leaves and other green parts. Light green or yellow patches of various shades, shapes and sizes appear in affected leaves. These patches may form characteristic mosaic patterns, resulting in general reduction in growth and vigour of the plant.