Definition

A marginal leaf blight is is sudden, severe, and extensive spotting, discoloration, wilting, or destruction of leaves starting at leaf margins.

Above: Xanthomonas marginal leaf blight of Syngonium podophyllum.

Discussion

Natural leaf openings at leaf margins, i.e., hydathodes, can serve as a point of entry for some plant pathogens, especially bacterial cells of the genus Xanthomonas, leading to marginal leaf blight. 

However, marginal leaf blight symptoms can be an indication of a number of plant health problems, including severe nutritional deficiency (e.g. potassium), root rot, phytotoxicity or fertilizer burn, vascular disease, and/or drought.