Stake tomato plants to keep them off the soil, mulch to reduce water splashes, and remove or deeply dig in old crops after harvest. Cultural techniques can help to reduce the risk of late blight outbreaks. At this point, there is no biological control of known efficacy for use in suppressing late blight. The most important way of controlling late blight is to prevent its spread. If Irish potatoes have been grown in a field, infected tubers remaining in the soil after harvest can be a source of the disease for crops that follow.Ĭontrolling blight once it has taken over is very difficult. Splashes of water can transfer the spores from plant to plant and wind can carry the spores greater distances. Spores are the mechanism for the rapid and devastating spread of late blight when conditions are cool and moist. As infected tubers and perennial weeds germinate and grow, the fungus becomes active and reproduces on the young plants. The fungus can also survive in perennial weeds, such as nightshade. The late blight fungus survives in infected potato tubers in the ground or in cull piles and in infected tomato fruits and crop debris. The fungus becomes inactive during dry periods. Daytime temperatures between 15 - 21° C, night temperatures between 10 - 15☌, and relative humidity near 100% create ideal conditions for infection and spread of the disease. The disease can spread rapidly during cool, rainy weather, killing plants within a few days. Although late blight can occur at any time during the growing season, it is more likely to be seen during cool wet seasons. Late blight of potato and tomato is caused by the fungus Phytophthora infestans. Patches of infected plants have a characteristic odour as a result of the rapid breakdown of plant material. Active late blight spots are not zonate and typically do not have definite concentric rings. Early blight symptoms are more circular, larger and darker than late blight marking and have a definite concentric ( zonate) margins. Late blight is sometimes confused with early blight ( Alternaria solani). Late blight symptoms can be mistaken for several other diseases. Infected potato tubers exhibit wet and dry rots. In moist weather, a white downy fungal growth may appear on the affected fruit-rot surface. On tomato fruit, grey green watery spots can develop on the upper half of the fruit, which later spread and turn greasy brown and bumpy. Note scorched appearance of leaves, stems and fruits. Stems can also develop elongated, greyish watery brown lesions. In dry weather, affected foliar parts may appear dry and shrivelled. In moist conditions, a downy white greyish mould usually develops near the margin of leaf spots on the underside of leaves. The spots may enlarge rapidly until entire leaflets are killed. Leaf spot margins often are pale green or water-soaked. On leaves, pale green to brown spots, sometimes with a purplish tinge, appear on the upper surface of leaves. In potatoes, tubers can also be infected. Late blight symptoms can develop on leaves, stems, branches, and in case of tomatoes on both green and ripe fruits. When conditions favour development of late blight and there are no steps taken to suppress the disease, it can completely destroy the above-ground parts of plants (stems, leaves, tomato fruits) and can also affect potato tubers. It is known as the most devastating disease of potatoes. Late blight of potatoes or tomatoes can be devastating with dramatic and disastrous economic consequences. Late blight is a fungal disease that can affect many vegetables of the Solanum species, mainly potatoes and tomatoes, but also eggplants.
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