Septoria tritici blotch (STB) or speckled leaf blotch, caused by Mycosphaerella graminicola (anamorph Septoria tritici), is one of the most important foliar diseases of wheat worldwide. Losses to STB can reach 50% in disease-conductive climates. Infection by M. graminicola requires cool temperatures (15-25°C) with humid conditions. In the developing world, STB can be severe in North Africa, parts of South America, and Central and West Asia. The presence of wheat stubble, volunteer wheat, and susceptible grasses sustains the survival of the disease from year to year.