Gray Leaf Spot
About the Disease: The gray leaf spot is characterized by graying of leaves and the appearance of black colored specks throughout the foliage.
Symptoms: Numerous lesions are formed on the leaves. Thus the leaves can completely turn yellow and then brown and fall off. These lesions will not coalesce. Since there are no leaves to provide shade to the plant, the fruits in the plant will be completely burnt. The plant will become totally unfit for usage. This kind of a gray leaf spot is commonly seen in plants like tomato. Excessive defoliation is the predominant feature.
Along with the leaves, the petiole and the stem regions can also get affected rarely. Lesions may form even in the stems. In this case fruits will not get affected. Both the older as well as the newly formed will develop brown spots throughout the layer of the leaf (both upwards and underneath). Initially lesions form and they gradually increase in size, till it reaches 2 mm and forms large spot across the leaf surface. IT is called the gray leaf spot, since these spots have a central gray area. This will be encompassed by a yellow colored region. In some severe cases, the gray spots will fall off, leaving a small hole in the center of each spot.
Pathogen Involved: The main pathogens that are involved in causing this disease includes the Stemphylium solani and S. lycopersici.
Time of Occurrence: This mainly occurs when there is a very long period of rainy season. When the dew settle on the plants for a very long time and when the temperature is around 20 degrees in Celsius, the disease can occur.
Conditions Favoring Disease: The pathogens can easily thrive on the dead plants or on other hosts like Brinjal plant, weeds or solanaceous plants. Pepper plants can also serve as a host. The spores of the fungus will get dispersed by wind. Young seedlings will get affected first. Temperature of 20 to 30 degrees and excessive rain are favorable condition for this disease. If you practice overhead spraying of water instead of furrow irrigation, the plants will surely get affected by this disease.
Disease Management: The plants need to be inspected regularly for fungal growth. Fungicides have to be applied regularly. Shady areas need to be avoided for plant growth. There must be proper ventilation and raised seedbeds can be used. There must be proper crop rotation. The same solanaceous must not be continuously cultivated in an area. It must be exchanged with other crops.