June 2009. Leaf spots on lettuce from ?Kenya; what is it and how could it be controlled?

It was difficult to say much from the photo, but if the spots are zonate, it is possible that they are an
Alternaria species. Look for velvety brown growth on the back of the spots.

The University of Florida sight says: Symptoms: Small circular spots are formed, the centers of which gradually dry and turn black. Production of spores increases the black appearance of the spots. Leaf lesions often exhibit a zonate appearance.

Rarely an economic problem in Florida; however, the use of maneb fungicides to control downy mildew on lettuce or endive will aid in control of this disease.

http://edis.ifas.ufl.edu/PG048

It does not look like Septoria blight. If it were you should be able to see black fruiting bodies of the fungus.

www.umassvegetable.org/soil_crop_pest_mgt/disease_mgt/lettuce_septoria_blight.html