Late Blight – Symptoms, Prevention and Treatment

Brownish-green spots appear on the leaf margins and leaf tops. Later, large areas of the leaves turn brown completely. During wet weather, lesions on the lower side of the leaves may be covered with a gray to white mouldy growth, making it easier to distinguish healthy from dead leaf tissue. As the disease progresses, the foliage runs brown, curls and dries. In some cases, the sharply delimited brown spots and the white covering also appear on the stems, branches, and petioles. Greyish-green to dirty-brown and wrinkled stains appear on the fruits. At these spots, the fruit flesh is hardened.

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Causes

The risk of infection is highest in midsummer. The fungus enters the plant via wounds and rips in the skin. Temperature and moisture are the most important environmental factors affecting the development of the disease. Late blight fungi grow best in high relative humidity (around 90%) and in temperature ranges of 18 to 26°C. Warm and dry summer weather can bring the spread of the disease to a halt.

Hosts 

Prevention

• Purchase healthy seeds from reliable retailers.
• Plant more resilient varieties.
• Tomatoes and potatoes should not be cultivated next to each other.
• Try to keep plants dry through good drainage and ventilation of your cultures.
• Install a simple transparent rain shelter with the help of a tarpaulin and wooden stakes.
• Use plant fortifier for general strengthening of the plants.
• Crop rotation of two to three years with non-host crops is recommended.
• Silicate-containing fertilizers may increase the resistance to the fungus, especially in the seedling stage.
• Avoid irrigation late in the day and irrigate plants at ground level.
• Disinfect field equipment and tools.

Treatment