Plant Diseases
Wheat Diseases in Arkansas
Tan Spot
Tan spot, caused by the fungus, Pyrenophora tritici-repentis, is a relatively
new disease in Arkansas and not very widespread. Symptoms on the leaves first
appear as tan-brown spots that expand into oval tan blotches with yellow
borders. Several lesions may grow together to kill large areas of a leaf, and
the lesions become darker as they mature because of the production of dark brown
spores. Symptoms on leaves can be confused with Septoria leaf blotch, but no
pycnidia are produced in tan spot lesions.
Initial inoculum comes from sexual spores produced in fruiting bodies on
infected stems from the previous wheat crop. These fruiting bodies are large,
black and feel like rough sandpaper if one slides an infected stem between one's
fingers. Finding these fruiting bodies on the crop debris is a good means of
diagnosis because these should be evident if tan spot is a problem in a field.
Tan spot is readily controlled by crop rotation and tillage to bury and
decompose the crop debris. Resistance levels of commercial varieties is not
known. Tilt foliar fungicide is effective against tan spot.
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