Water-soaked and small chlorotic lesions appear on the lower leaves of the plant. The disease emerges from the lower leaves up to the flag leaf. Later, the lesions become tan-brown, oval- or irregular-shaped leaf blotches with yellow margins. As the disease progresses, tiny brown fruiting bodies in the enlarged gray lesions can be seen using a magnifier or a microscope. Badly affected leaves die back from the tip as the blotches converge. After flowering, wet weather can lead to lesion development on the glumes. Symptoms often start at the tip, but whole areas may be covered with dark brown to dark purple lesions with ash gray areas ( “glume blotch”). Severe infections may result in lightweight, shriveled kernels. Infected seeds show irregular emergence and seedlings have brown shoot tips.
This foliar disease is caused by the fungus Parastagonospora nodorum, which survives on wheat straw, infested seeds or on alternative host crops. The fungus is dispersed through water and requires about 12 to 18 hours of leaf wetness for infection. Older leaves near the soil are the first affected. Then, the fungus is dispersed via wind or rain-splashes to the upper parts of the plant and to neighboring crops. Late season infections could lead to glume blotch if the disease is moving up the canopy. It causes shriveled grains and reduces yield. Spores are spread by wind and can cover long distances to infect the seedlings in other fields later in the season. This leads to earlier infection of the following crops and to irregular emergence. The life cycle of the fungus is stopped at temperatures below 7°C. Optimal growth range is between 20°C and 27°C.
Sorry, we don't know of any alternative treatment against Phaeosphaeria nodorum . Please get in touch with us in case you know of something that might help to fight this disease. Looking forward to hearing from you.
Chemical treatment of the disease may be effective to reduce the risk of an outbreak but may be inviable in smaller farms. If fungicides are needed, products containing difenoconazol, triadimenol or fluquinconazol can be applied. The application method varies depending on time of occurrence and cultivation type.