When no leaf moisture is present, infection sites quickly dry out and develop yellow margins that later turn red brown. Older lesions will develop ashen gray centers with small black specks, which are the pycnidia. The pycnidia harbor spores that disperse with splashing raindrops spreading the disease to healthy plant tissue. These black specks are visible to the eye and serve as a good diagnostic tool. See photo 34 .
Spring wheat is susceptible to tan spot while barley is a poor host.
Tan spot develops initially as yellow-tan flecks on both upper and lower leaf surfaces. The lesions expand into lens-shaped tan blotches with yellow borders. A characteristic of tan spot is a small, dark brown center. Lesions may coalesce and form larger ones. See photo 35 .