Control Measures:Following measures should be taken to control this disease:
- The seed grains should be treated with organomercury disinfectants before sowing.
- -lot water treatment should be given to the seeds. The grains should be sub-merged for 10 minutes in water at a temperature vtween 52°C and 54°C. The temperature should be kept within these narrow limits. Below 52°C the fungus is no: killed. Whereas above 54°C the embryo of the seed is injured.
- Sun treatment: This is a modification of the above method. This s practiced where the summer temperature is very high. The suspected seeds are soaked in water and exposed to thc heat of he summer sun for 4 hours (from 8A.M. to 12 noon).
- Copper dust and sulphur dust should be sprayed on plant
- Grow the resistant varieties of wheat and other plants.
Downy mildew (Grapes, Bajra)
Causative agent: Plasmophara vilicola (Grapes)„Meracporci graninicola (Bajra)
AlTicted plants: Grapes and Bajra
Syn. ptoms: The early symptom of the disease is the appearance of sma.I greenish yellow oily spots on the dorsal surface of tin leaves. The spots gradually increase in size. They fuse and become brown. The sporangiophores of downy mildew appear on the !owe; surface of ti e leaves. The infected leaves dry up. They become brittle and fall AT. The disease spreads to other parts of the plant. The berries shou brown patches with downy growth. Their colour turns to grayish brown or dark-brown.
Environmental Relationship: Moist weather is suitable for the attack of this disease. But this disease disappears in dry hot weather. Hos ...parasite Relationship: Downy mildew is an obligate parasite. Its mycelium is intercellular. It sends haustoria into the host cells. Disease cycle: The fungus survives as oospore in the dead plant. Or its mycelium survives in the perennial hosts. The sporangiophore coin :s out through stomata. The sporangia produce zoospores. Zoospore dispersed by wind. The zoospores enter through the storr ata.
Control measures: Bordeaux mixture should be sprayed on the plan for controlling this disease.
Powdery mildew (Grapes, Barely, wheat)
Causal agent: Uncinula necator (Grapes), Etysiphe graminis (wheat barely)
Symptoms: This diseases cause malformation and discoloration of leaves. It forms whitish-grey patches on the upper or under surface. The affected parts of the stem are at first whitish-grey. But later they turn dark brown. The berries or grains become irregular in dmpe. It is reduced in size and develops cracks. The plant shows dwarfed appearance.
Host-parasite Relationship: The mycelium spreads over the host i.e., stern, leaves and fruits. The hyphae are attached by aspersoria. Aspmsoria sends haustoria into the epidermal cells of the host to abscrb food. The superficial mycelium gives the plains dusty powered appearance.
Environmental Relationship: Wind, dry weather, low hum dity and cloudiness promote the disease.
Dist ase-cycle: The disease is air-borne. The conidia and asimspores are carried by the wind to other hosts.
Control measures: The plants should be dusted with fine sulphur at regular intervals to control this disease. All diseases plants should be dest tayed. Applications of copper containing spray also control this disease.
Damping off disease (Tobacco)
Causative Agent: Pythium de Baryanum, P. myriotylum.
Affected plant: Tobacco
Sym ptoms: Diseased plants turn pale-green. They show a girdle of brown colour near the surface of the soil in the region of hypocotyls. The:’ collapse due to the weakening of tissue at the base of the stem. Environmental Relationship: Disease spreads in poorly aerated and watt r-logged soils at high temperature.
Disease cycle: The pathogen survives in the soil as oospore. Oospore germinates to produce zoospores. The zoospores attack fir:. young seedling. The host shows disease symptoms in the region of hypocotyl near the ground level.
Control measures: Soil should be sterilized. Good drairage and proper aeration of the soil retard this disease. The seeds should be treated with copper carbonate, copper chloride and formalin.