Late blight — Tomato

Symptoms

All aboveground plant parts may be affected. Leaves develop small to moderately sized, irregular pale-brown patches, approximately 2–10 mm initially, sometimes with a purplish tinge. Lesion margins are pale green or water-soaked. Lesions enlarge and merge rapidly, potentially killing entire leaflets. Under moist or humid conditions, white, downy fungal growth appears near the lesion margins on the lower leaf surface. Disease progression can be extremely rapid, resulting in severe defoliation across entire fields within approximately two weeks under favourable conditions. In dry weather, affected plants may appear scorched, with shrivelled foliage, although disease progression slows or stops. Stem and petiole lesions are dark brown and water-soaked; fungal growth may occur on them. Stem lesions may kill entire sections of the plant or remain superficial and dry out. Fruits may be infected at any stage of development, often beginning near the stem end. Fruit lesions are olive-brown with a rough, leathery surface and may spread until the entire fruit is affected. Infected fruits initially remain firm, with uneven discoloration of internal tissues. White fungal growth may develop on affected fruit surfaces under humid conditions. Secondary organisms may invade the lesions, causing soft rot.