Septoria Tritici Blotch

Symptoms usually begin as small chlorotic (yellowing) flecks that develop into irregular, tan-to-brown blotches with a somewhat angular outline, often bounded by leaf veins. As the lesions age, numerous small dark pycnidia become visible within the dead tissue, giving it a speckled or peppered appearance that is the most reliable field diagnostic feature.

Zymoseptoria tritici survives between crops on infected wheat residue and on volunteer plants. From this residue it produces wind-dispersed sexual spores (ascospores) that can initiate infections over distance, while asexual spores (pycnidiospores) formed in pycnidia are moved shorter distances by rain splash within and between plants, driving the disease up the canopy.

• Infected crop residue and volunteer wheat carry the fungus between seasons
• Wind-dispersed ascospores can start new infections across a region
• Rain-splashed pycnidiospores move the disease from lower to upper leaves
• A long latent period allows infection to build before symptoms appear

Wheat is the principal host, with triticale also affected to a lesser degree. Disease pressure is greatest in cool, humid regions where rainfall keeps the canopy wet and provides the splash events the pathogen needs to spread upward. Early sowing, dense canopies, and susceptible varieties all tend to increase risk.

• Cool, wet, humid weather with frequent rainfall and prolonged leaf wetness
• Early autumn sowing that exposes crops to more infection cycles
• Dense, lush canopies that stay wet and favour splash dispersal
• Susceptible varieties and short rotations that keep inoculum high

Management is built on integrated tactics that reduce inoculum and slow the disease reaching the upper leaves, rather than on any single measure. Resistant varieties are the foundation, supported by cultural practices and, where justified, protection of the upper canopy under locally authorized guidance.

• Choose varieties with good resistance ratings for the local region
• Use crop rotation and residue management to reduce carry-over inoculum
• Consider later sowing where agronomically suitable to reduce early infection
• Avoid excessive nitrogen that produces dense, humid canopies
• Monitor upper leaves closely from stem elongation through heading