Septoria tritici blotch of wheat

Septoria tritici blotch is a common disease of wheat, often occurring alongside other foliar diseases. It is also known as Septoria leaf spot and is caused by Zymoseptoria tritici. Elliptical, tan-brown lesions that often have yellowish halos first appear on seedling leaves. Lesion centers die and dark fruiting bodies are produced, giving the lesion a characteristic speckled appearance. Subsequent lesions on higher leaves generally follow leaf veins, having straight edges and no yellow margins. When humid, a translucent, curling thread of whitish ooze may appear from fruiting bodies. This ooze is visible with a hand lens, and disperses when contacted by rain or dew. Symptoms can be observed from tillering stages through ripening. Septoria tritici blotch lesions generally do not have pronounced chlorotic halos like Stagonospora leaf and glume blotch and tan spot, and lesions are more elongated with rougher edges.

Elliptical, tan-brown lesions of Septoria tritici blotch. Image: M. Burrows. 
Foliar symptoms of Septoria tritici blotch. Image: C. Grau.

The fungus overwinters on seed, residue, and overwintering cereals. Cool, wet weather favors infection. During spring, spores are produced and infect other leaves by rain-splash. Disease will progress through infection cycles as long as the weather remains cool, wet, and rainy.

Plant varieties less susceptible to Septoria tritici blotch. Practices that encourage residue decomposition and crop rotation can be effective disease management strategies. Fungicides are labeled for management of Septoria tritici blotch. Scout and consider factors such as varietal susceptibility, forecasted weather, length of rotation away from wheat, and yield potential prior to fungicide application.

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Gallery images: C. Grau and M. Burrows.