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Crop Diseases: How to Identify, Control, and Prevent
Diseases of Crop Plants
Our environment contains a variety of pathogens. When they get favourable conditions for their growth and propagation, they spread and infest the crop plants causing diseases.
Depending upon their mode of occurrence, crop diseases are of the following four main types:
1. Seed-borne Diseases: These diseases spread through seeds, e.g., “ergot of bajra” or of pearl millet; “leaf spot of rice”; “loose smut of wheat”; red rot of sugarcane; – all are caused by fungi.
2. Soil-borne Diseases: These diseases spread through the soil and mostly affect the roots and stems of crop plants, e.g., “smut of bajra,” “tikka disease of groundnut”.
3. Air-borne Diseases: These crop diseases are transmitted by the air, e.g., “rust of wheat”, “blast of rice”, etc.
Airborne diseases attack all aerial parts of the plants, e.g., leaf, flower, and fruits.
4. Water-borne Diseases: Pathogens of these crop diseases are transmitted by the water, e.g., “bacterial blight of rice”.
Control of Crop Diseases
All the seed-borne and soil-borne diseases can be controlled by treating the seed or soil. Airborne diseases are controlled by spraying fungicide solutions on infested parts. Diseases of the major crops and their control measures have been given in Table.
Diseases of Major Crops, Their Symptoms, and Control Measures
| Name of the Crop | Disease | Pathogen | Symptoms | Control Measures |
| 1. Rice (Paddy) | Blast | Fungus, Pyricularis oryzae | Brown boat-shaped lesions (spots) appear on the margins of leaves. | 1. Seed treatment with Thiram 2.5 g/kg seed. 2. Spray Bavistin (1 g/l water) at 10 days intervals. |
| 2. Wheat | Rust | Fungus, Puccinia graminis | Yellow, brown or black elongated spots appear on leaves and straws. | Spray Dithane M45 at 2 g/l water at 10 days intervals. |
| 3. Chickpea | Wilt | Fungus | The leaves become yellow and dry up.
Roots turn black and decompose. |
Deep sowing at 8-10 cm depth in the light soils. |
| 4. Pigeon pea | Stem rot | Fungus | Development of brown to dark brown lesions on the stem near the soil surface. These lesions girdle the stem and the plant dies. | 1. Grow sorghum and pigeon pea mixed cropping. 2. Avoid water logging. |
| 5. Mustard | 1. White Rust | Fungus | White or cream-yellow scattered pustules appear on the lower surface of leaves. | Spray Dithane Z.78 or Dithane M45 at 2g/l water. |
| 2. Downy mildew | Fungus | Yellow irregular spots appear on the leaves. In severe infection, the inflorescence is malformed, twisted, and covered with white powder. | Spray the crop with 0.2% Ziram or Maneb |