As the lesions enlarge, they become dark brown and the centers turn grayish-white in color as tiny brown pycnidia develop within them. The fungi survive on wheat stubble and other wheat residues and volunteer wheat plants. These fungi survive from one crop to the next as mycelium in living, volunteer plants or as pycnidia on wheat residues. The fungi can survive up to three years in wheat stubble on the soil surface. S. nodorum infects seed and is thus seed borne.
Seed borne inoculum can be sufficient to initiate epidemics.
Septoria nodorum leaf blotch. Note oval lesions with dark centers and yellow halos. Infections require 6 hours or more of leaf wetness. The wheat plant is more susceptible to infection by S. nodorum at later growth stages, usually during and after heading, whereas S. tritici is more common on plants earlier in the spring during stem elongation to flag leaf emergence. Spread of both fungi is favored by wet, windy weather.