Final diagnosis


Marginal necrosis (tipburn)

Several moist, blackish lesions formed on the periphery of the leaf blades of several heart leaves of this lettuce. (<b>marginal necrosis</b>)
Detail of a rather extensive brown lesion, located at the edge of the leaf blade of a lettuce leaf; note the browning of the small veins present nearby. (<b>marginal necrosis</b>)
Marginal necrosis can lead to the formation of wide fringes of necrotic tissue at the edge of the limbus; these will dry out if weather conditions permit.
Brownish to necrotic lesions have formed along the lower leaf margins of this lettuce, rendering it unmarketable. (<b>marginal necrosis</b>)