Leaves of seedlings and tillering wheat plants can become severely diseased during warm wet springs, however, farmers may not notice tan spot until flag leaf emergence or early heading. Seed infection is also favoured by wet weather during grain filling if large numbers of air-borne spores are present. Conditions favourable for seed infection and red smudge development do not occur every year. Tan spot can infect crested and intermediate wheatgrass, Russian and Altai ryegrass, bromegrass, and other grass hosts. Rye and barley can also be infected, however, the disease does not develop significantly enough to affect yields.
Oats are immune to tan spot infections.
The impact of alternative hosts as sources of inoculum on disease outbreaks in wheat grown in Saskatchewan has not been determined. Disease Management Seed Planting seed containing large numbers of red smudge kernels can result in reduced emergence, poor establishment and vigor of infected plants and should be avoided. Planting red smudge kernels does not necessarily affect the severity of tan spot on the wheat seedlings. Tillage Conservation tillage practices retain soil moisture but can leave large quantities of tan spot infested stubble and straw on the soil. Leaf spotting diseases caused by stubble-borne pathogens tend to be more severe under conservation than conventional tillage systems when environmental conditions favour disease development.