Cercospora Leaf Spot of Groundnut
Cercospora leaf spot of Peanut also known as Tikka disease is one of the most important diseases of this crop. All parts of the host plant above soil level are attacked by the disease. The first visible symptoms appear on the leaflets of lower leaves as dark brown spots which at a later stage, are surrounded by yellow rings. These are called Cercospora early leaf spot. Cercospora late leaf spot is recognized by circular black spots without yellow hallo. As the disease progresses the spots enlarge until the entire leaf is affected. Due to excessive spotting of leaves there is defoliation and weakening of plant resulting in fewer and smaller sized pods and loss in yield. Tikka disease is caused by two fungi, Cercosporadium personatum and Cercospora arachidicola both mostly occurring on the same leaves. The former appears about 30 days earlier than the later. However, Cercosporadium personatum is more dangerous than Cercospora arachidicola because it produces many more spots and its rate of progress is so much more rapid than that of Cercospora arachidicola that it becomes the major factor in the severe epidemic. Thus Cercosporadium personatum by causing defoliation affects size and quality of nuts.
- Crop rotation with millets, sorghum or other kharif crops minimize disease incidence in next season,
- Burning of previous year’s diseased plant debris will, to a great extent, reduce the source of primary infection.
- Disease resistant/ tolerant variety mostly approved varieties are tolerant leaf spot disease.
- Chemical control: Application of mancozeb as protectant is very suitable.
2. Crown Rot
Pathogen of this disease attacks peanut plant at three stages of plant growth: 1. Before emergence 2. At seedling stage and 3. Adult plant stage. Pathogen conidia attached to seed or present in soil attack seed before emergence and cause rotting of seed. Pathogen produce black mass of spores and seed become soft and watery. The pathogen attacks young seedling and produce circular brown spots on cotyledons When pathogen attacks young seedling. The symptoms spread up and downward stem and root. Brown symptoms appear on crown region with profuse growth of fungal conidia. The affected portion become soft, rotten and some time show shredding symptoms. The disease when appears in adult plants show crown rot symptoms. Large lesions develop on the stem below the soil and spread upwards along the branches causing drooping of leaves and wilting of plant.
Carbendazim when used as seed treatment gives more than 75% disease control. This fungicide gives more than 90% disease control when it is applied as drenching in root zone at initial stage of disease. Initial stage of disease may be diagnosed by closed leaves in early hours. Groundnut plant closes its terminal leaves at noon during hot summer but diseased plants show this symptom in early hours. An observer may detect these symptoms by keeping sun on his back and diseased plant will show slivery closed leaves and such plants may treated with fungicide.