Entire leaves die and infections quickly spread to petioles and young stems.
Late blight is found when humid conditions coincide with mild temperatures for prolonged periods. If conditions are ideal for disease development, disease development is rapid and losses can be severe. Spores of the fungus are easily spread by wind to other plants. Disc tomato fields in fall to eliminate a winter reservoir for the fungus. Avoid sprinkler irrigation, if possible, because it favors the development of late blight.