Late blight infection at the base of the stem initiated by infected seed. This symptom looks similar to blackleg (see page 87). (In humid weather, no white mycelium develops on plants infected with blackleg.)
Late blight symptoms on stems are irregular, dark-brown to black lesions. Under humid conditions, fungal mycelium and spores develop on infected areas.
Stem lesions expand rapidly in humid weather and can cover most of the stem.
Infected stems are brittle and break easily.
Seed ball infected with late blight
The right half of the field was killed by late blight.
Note the regrowth of healthy shoots after the
infected plants died.
The tender growing point is an easy target for late blight because
moisture persists there after a heavy dew, rain or irrigation.