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Tomato Late Blight

Tomato Late Blight

Phytophthora infestans

fungi

In a Nutshell

    Brown spots grow from the leaf marginsWhite covering on the underside of leavesGrey or brown wrinkled stains on fruitsHardened fruit flesh and fruit decay

Hosts: %1$s

· Tomato

Symptoms

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 moldy 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.

Trigger

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 humidities (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.

Biological Control

At this point, there is no biological control of known efficacy against late blight. To avoid spreading, remove and destroy plants around the infected spot immediately and do not compost infected plant material.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Use fungicide sprays based on mandipropamid, chlorothalonil, fluazinam, triphenyltin, mancozeb to combat late blight.

Preventive Measures

    Purchase healthy seeds from reliable retailersPlant more resilient varietiesTry to keep plants dry though good drainage and ventilation of your culturesInstalling simple transparent rain shelter with the help of a tarpaulin and wooden stakes might helpAvoid irrigation late in the day and irrigate plants at ground levelCrop rotation of two to three years with non-host crops is recommendedTomatoes and potatoes should not be cultivated next to each otherSilicate-containing fertilizers may increase the resistance to the fungus, especially in the seedling stageDisinfect field equipment and toolsUse plant fortifier for general strengthening of the plants