Tan spot (Pyrenophora tritici-repentis)

Tan Spot

Tan spot: biology

The pathogen overwinters on crop residue and produces airborne spores in the spring which are carried to young plants. Early infections lead to further sporulation and spread during the growing season. The development of the disease is inhibited by hot dry weather, hence why fields with severe infections in the spring show little to no tan spot on the upper leaves at the end of the season. Seed infection is not important for disease spread.

Tan spot: damage description

Tan spot lesion

Tan spot lesion

Tan-brown spots on leaves

Tan-brown spots on leaves

Initially small tan-brown spots develop on leaves. These expand to tan, oval to irregularly shaped, lesions with a dark brown centre surrounded by a yellow zone. Spots can coalesce killing the leaf. Tan spot is easily confused with Septoria leaf spot but tan spot usually involves lesions with a brownish centre and no black dots. The pathogen can attack the head and infect kernels causing pink seed. However, pink seed can have other causes.

Conditions which favor good crop growth also favor disease development. Losses are due to shriveled seed and reduced seed yield.

Tan spot: management

Allow several years between susceptible crops. If available, use resistant varieties; common wheat is less susceptible than durum. Burying crop residue may reduce disease severity. Foliar-applied fungicides will reduce losses but crops should be monitored closely around flag leaf emergence and sprayed when only small spots are present on upper leaves.

Recommended solution

Quilt®

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