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Barley net spot
Barley net blotch is a fungal disease primarily affecting the leaves and leaf sheaths, with less frequent infection of the stems. In seedlings, lesions typically appear more than 1-2 cm from the leaf tip, while in adult plants, symptoms often begin at the base of the leaves, causing the leaf tips to turn yellow. The brown spots on the affected areas have an unclear boundary, and they form a network-like pattern in both vertical and horizontal directions. As the number of lesions increases, they may merge into stripe-like patterns and produce a small amount of spores. Infected glumes develop irregular brown spots.
The pathogen responsible for this disease is *Drechslera teres* (Sacc.) Shoem., also known as *Helminthosporium teres* Sacc. Its sexual stage is *Pyrenophora teres* (Died.) Drechs. This fungus belongs to the Ascomycota subphylum. The conidia are pale olive in color, cylindrical, and range from 30 to 175 μm in length with 1–10 septa. They are usually found singly or in groups of 2–3, straight, with only a slight bend at the top. Ascostromata form on infected plant tissues. These structures are dark brown and nearly elliptical, measuring 430–800 × 300–600 μm. The ascospores are colorless, rod-shaped, and contain 8 or sometimes 4 ascospores. They are brownish-brown, nearly elliptical, and measure 40–62.5 × 17.5–27.5 μm.
The disease spreads through several pathways. Mycelium can remain latent within the seed coat, and spores can attach to the surface of seeds, serving as primary infection sources. Additionally, ascospores produced on diseased plant parts can infect new hosts. Seed-borne pathogens cause seedling diseases, and spores released from infected tissues can reinfect via wind and rain, potentially damaging the flower parts and leading to seed contamination. Once mature, the fungus forms ascospore-containing structures on infected materials such as wheat hulls. The pathogen can survive for up to 7 years in soil or crop residues. Spore germination occurs best at temperatures between 20–25°C, with 100% relative humidity promoting rapid infection. Cool temperatures, low light, and high humidity conditions are favorable for disease development. Winter barley is particularly susceptible, with higher incidence rates observed in winter-sown crops.
To manage the disease, several control methods are recommended. First, planting disease-resistant barley varieties such as Early Maturing No. 7, Liang Erling, and Zhe Nong 8 can significantly reduce the risk. Timely sowing is important to avoid continuous cropping and reduce disease buildup. For chemical control, soaking seeds with TH88 (2 ml per 20 kg of water) and treating 10 kg of barley seeds for 24 hours is effective. It is important to conduct this process indoors or under controlled lighting to prevent photolysis. Other seed treatments can be applied as needed. In the early stages of disease, spraying 50% carbendazim WP diluted at 800 times, 60% anti-mildew WP at 1000–1500 times, or 70% mancozeb WP at 500 times can help manage the infection effectively.