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Tan Spot


© Kansas State University, Department of Plant Pathology

Pathogen(s) causing disease:

Helminthosporium tritici-repentis (Drechslera tritici-repentis, Pyrenophora tritici-repentis)

Symptoms:

Tan-brown, flecks on upper and lower leaf surfaces expanding to blotches 12 mm long (often with yellow borders). Fungal fruiting bodies (pseudothecia) are visible as dark raised specks on wheat straw.

Conditions:

The tan spot fungus oversummers and overwinters in old wheat residue. Very small (approximately 1/64"), raised, black fungal fruiting bodies are often abundant on old residue. These fruiting bodies produce ascospores in early March that are shot a short distance (less than 6") from the fruiting body during spring rains.

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© Purdue University, Plant and Pest Diagnostic Laboratory
If the ascospores land on a young wheat leaf, they germinate and initiate primary infections. Infection requires a moist period ranging from 6 to 48 hours, depending on temperature. Severe infections are usually limited to continuous wheat fields with lots of wheat straw on the soil surface. Rye and several species of bromegrass and wheatgrass are alternative hosts of the tan spot fungus.

Management:

Crop rotation, tolerant or resistant varieties, destruction of wheat stubble, fungicides.

Sources:

Kansas State University
Purdue University

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