Tan spot of wheat

C/O: Pyrenophora tritici-repentis

Symptoms:

• Small, oval to diamond-shaped spots.
• These spots will enlarge and turn tan, often with a yellow border, and have a small dark brown spot resembling an “eyespot” near the center.
• Eyespot symptom is best observed when holding the leaf up to the sunlight.
• Infected kernels can develop a reddish discoloration on the seed coat, which commonly is called “red smudge”.

Etiology:

• Conidiophores are erect, simple (not branched), have a swollen base, and are olive-black in color.
• Conidia are hyaline (non-pigmented) to light brown, cylindrical, and have one to nine transverse septa.

Favorable condition:

• Wet periods (24 hours or greater), large numbers of conidia form in the disease spots, and conidia may be blown onto other wheat leaves to form new infections.

Survive and spread:

• Survive: black pinhead-sized fruiting structures (pseudothecia), conidia also previous season crop.
• Spread: spores are dispersed by wind.

Management:

• Resistance cultivar
• Foliar spray fungicide: pyraclostrobin, metconazole, propiconazole, prothioconazole, tebuconazole, prothioconazole + tebuconazole, metconazole + pyraclostrobin, propiconazole + azoxystrobin, and propiconazole + trifloxystrobin.
• Seed treated fungicide: thiram, triticonazole, and carboxin.