Tan Spot (also known as yellow leaf spot) spores spread by wind from overwintering structures in crop residue. Small, dark brown to black spots first appear on lower leaves. Tan, oval-shaped lesions develop along the veins and a central dark spot with a light halo is often present. Tan spot reduces the photosynthetic area of the leaves and may cause yield loss, particularly when upper leaves are affected. Conidia are produced on old lesions on wet leaves and becomes air borne as the leaves dry. The fungus requires six hours of leaf wetness to infect and colonize new leaf tissue. Don’t confuse tan spot and Septoria symptoms, which look very similar. Remember tan spot lesions never develop pycnidia (fruiting bodies). Wheat grown in Canada is susceptible to both tan spot and Septoria, so rotation to non-host crops - canola, flax, corn, soybeans, potatoes or alfalfa can help.