Yellow leaf spot [Drechslera tritici-repentis]
Wheat, durum wheat, triticale, rye.
Pattern of damage
The primary infection, originating from straw and stubble residues, causes rounded, pale brown spots on the leaves close to the ground. The secondary infection leads to the formation of the typical dark brown infection spots surrounded by a chlorotic corona. Irregularly shaped leaf spots develop, that later grow together. The dark initial infection spots can still be recognized for a long time. Yellow leaf spot can only be clearly distinguished through its stromata, which stand individually on the leaf surface. At least 30 times magnification is required to distinguish it from Septoria nodorum, sooty mold and Alternaria.
Incorporate straw and stubble residues well. Promote soil organisms. Cultivation of more tolerant varieties.
Fungicide application ES 32-37 at the first visible sporulation. With high level of infection: a program of 2 applications at 3-week interval is required.
Spread/Transmission: The sexual reproduction stage survives on straw and stubble residues in the form of spherical brown pseudothecia. The life-cycles completed from the fall until the spring, whereby the peak of the ascospore ejection takes place in March/April since it requires humidity. It only spreads over a few centimeters or decimeters. Asexually formed conidiospores can be spread by the wind over greater distances. Temperatures above 20 °C promote epidemic spreading. Spore formation takes place on warm and humid nights, and spreading takes place by the wind on warm, dry days. Older leaves are more susceptible than younger ones.