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BROWN SPOT DISEASE OF PADDY
Brown spot disease, also called Sesame leaf spot, helminthosporiose, or fungal blight, is a major fungal disease of paddy.
The disease causes damage to the crop in many ways like :
Poor germination of seeds. Destruction of leaves, affecting the photosynthetic efficiency of the plant. Shrivelling and poor setting of seeds, reducing the market value of the produce.
Symptoms :- The disease affects both seedlings and mature rice plants. In seedlings, it causes blight.
In mature plants, the symptoms of the disease appear on leaves, leaf sheaths and glumes. Common symptoms include :- small, brown, and circular to oval spots on leaves. They take the form of long streaks in advanced stage.
The causal organism :- The disease is caused by the fungus Helminthosporium oryzae. Its mycelium consists of prostrate hyphae and erect conidiophores. The mycelium develops to a greyish brown or dark brown mat on plant parts. Conidiophores arise in tufts through the stomata. Helminthsporium oryzae produces a toxin, called cochlibolin.
Powdery mildew of rubber is very common in India and other rubber-growing countries. The disease appears predominantly on newly formed tender leaves during the refoliation period of rubber plants (during January to March). In India, the disease is severe in Kanyakumari, Idukki and Wayanad districts of South India, and also in the North-Eastern States. Cloudy days with light rains, or misty nights with dew formation during refoliation, favour serious disease outbreaks.
POWDERY MILDEW OF RUBBER
Symptoms :- An ashy powdery coating on leaves is a characteristic symptom. The leaves with ashy coating curl, crinkle, and their edges roll inwards. On older leaves, white patches later appear, causing localized necrotic spots or lesions, this reduces the photosynthetic efficiency. Infected flowers and tender fruits shed, affecting production. The clones RRIL 105, RRIL 118, RRIL 300, PB 217, PB 235, PB 280, PB 311 and 261 are highly susceptible to the disease. But, some clones, such as PB 86, RRII 208 and PB 310, show some tolerance.
Wettable sulphur (Carbendazim 2.5 g/l) is also effective in nurseries, and also for young plants as a spray. Bavistin 0.05% spraying is more effective than sulphur for nurseries and young rubber. Alternate use of Bavistin and sulphur is recommended to avoid resistance problem.
One of the worst diseases of tapioca. It is a viral disease, caused by tapioca mosaic virus which is transmitted by white fly ( Bemisia tabaci ). Symptoms :- The disease is characterised by a mosaic pattern on leaves, with light-green, yellow or white spots or patches on the green background of the leaves.
TAPIOCA MOSAIC DISEASE
In severe infection, the discolouration of the leaves may take striped, mottled, and circular patterns, with vein-clearing, vein-banding, and vein-thickening.
Initially, the affected leaves may show mosaic mottling.
Among the major diseases affecting black pepper, foot rot (quick wilt) is the most harmful one. Foot rot is caused by Phytophthora palmivora and is characterized by sudden rotting of collar, root & leaf, die back of twigs, spike shedding, & ultimate death of the plant.
QUICK WILT (FOOT ROT) OF PEPPER
The disease incidence is generally high when relative humidity is high and temperature is low. Piper colubrinum , P. obliquum , and P. guinense are reported to be resistant to the pathogen.
This disease is more prevalent during the monsoon season. The veins of the affected leaves may get discoloured and decayed, and often the entire branch may detach and fall. The veins of the basal portion are severely affected, leading to the rotting of that region. For this reason, the disease is also called 'foot rot of pepper’. Vein rotting seriously interferes with the conduction of nutrients with the result that the leaves turn yellow and finally they fall off and the plant becomes defoliated.
PREPARATION OF FUNGICIDES
Bordeaux mixture is an extensively used copper fungicide, commonly applied to control fungal diseases in plantation crops. It is a mixture of mainly copper sulphate and calcium hydroxide (quick Iime). Bordeaux mixture achieves its effectiveness by means of the copper ions (Cu2+) of the mixture. These ions affect enzymes in the fungal spores and prevent spore germination. This means that Bordeaux mixture must be used before the fungal disease has struck.
Preparation of bordeaux mixture (0.5 % or 1 : 1 : 100) Dissolve 50 g of powdered copper sulphate in 5 litres of water in a plastic bucket. Prepare milk of lime in another plastic bucket by dissolving 50 g of quick lime
in 5 litres of water. Pour the copper sulphate solution and the milk of lime from the above two vessels into a third one by gently stirring the mixture all the while. This will give a final volume of 10 litres of 0.5 % strength. The mixture is to be tested before use for the presence of free copper, which is toxic to the plant. Dip a polished knife in the mixture. If its blade shows a reddish colour add lime to the mixture till the blade does not show staining on dipping.
Tobacco decoction is a biopesticide, which is very effective for controlling aphids and other soft-bodied insects. It contains nicotine which acts as a contact poison to kill insects. Tobacco decoction can be prepared by boiling 500 g of tobacco wastes /leaves
