Disease dissemination is by wind and infected seed. The spread of
inoculum can be by pathogen contaminating corncobs, corn ears, corn debris
and/or alternate hosts. Following spore attachment and germination on the host
surface, the emerging germ tube remarked from spore polar develops to hyphae
and produce one or multiple appressoria. The infection peg develops from the
appressorium then penetrates directly through the cuticle and epidermis of the
leaf not often found through stomata (Martin, 2011, Knox-Davis, 1974). The
infection period occurs within 6 - 18h after spore attachment to plant leaves
(Lipps and Mills, 2002). In addition, the earliest detected disease symptom
appears 3 d after infection. The spindle shaped lesions are light brown to dark
brown, with a width of about 1.5-15.0 cm and are parallel to the midrib. The
symptoms first occur in the lower leaves and spread to the upper leaves. In
susceptible cultivars, many lesions are found and coalesce leading to severe
blight and death of plants. The disease spreads very quickly during warm
weather (24-30o C) and damp conditions (high relative humidity 80-100%). The
NCLB fungus can survive between seasons by mycelium and chlamydospores
in humus, leaves and corn seed (Abebe and Singburaudom, 2006).