Net blotch of barley

Systematic position and type of pathogen: Pyrenophora teres (anamorph: Drechslera teres) is a filamentous fungus belonging to the Ascomycota division. It is the primary causative agent of net blotch, a globally significant disease affecting barley crops worldwide, which leads to substantial losses in cereal production.

Diseases and crops: The pathogen primarily targets barley (Hordeum vulgare). The disease manifests in two distinct forms: the net form, characterized by dark brown longitudinal and transverse stripes forming a mesh-like pattern, and the spot form, which appears as dark blotches surrounded by chlorotic halos. These symptoms primarily occur on leaf blades but can also affect glumes and awns.

Biology and life cycle: The fungus overwinters as mycelium and conidia on infected crop residues, stubble, and occasionally on seeds. In spring, primary infection occurs when conidia are dispersed by wind or rain splashes. Throughout the growing season, multiple cycles of conidial production allow the pathogen to spread rapidly across fields, especially under frequent rainfall conditions.

Conditions for development and harmfulness: Development is highly favored by moderate temperatures ranging from 15 °C to 25 °C and extended periods of high leaf wetness. The harmfulness of the disease lies in the destruction of leaf tissue, which drastically reduces photosynthesis. This leads to reduced grain filling, lower test weights, and significant yield losses that can exceed 30% in highly susceptible varieties.

Protection and control measures: Effective management of net blotch requires an integrated strategy to minimize inoculum pressure:

• Planting resistant or moderately resistant barley cultivars.
• Implementing crop rotation to break the survival cycle of the pathogen.
• Management of crop debris through tillage to accelerate decomposition.
• Utilization of certified, fungicide-treated seeds.
• Foliar fungicide applications during critical growth stages (flag leaf emergence) when environmental conditions promote disease spread.