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Barley net spot
Barley net blotch, caused by *Drechslera teres* (Sacc.) Shoem. = *Helminthosporium teres* Sacc., is a common fungal disease that primarily affects the leaves and leaf sheaths of barley plants. In seedlings, lesions typically appear more than 1-2 cm from the tip, while in adult plants, the disease usually starts at the base of the leaves, with the tips turning yellow. The brown spots on the leaves have an unclear boundary, and under close inspection, a reticular pattern can be observed both vertically and horizontally. As the number of lesions increases, they may merge into stripe-like patterns and produce a small amount of spores. The glumes of infected grains often show irregular brown spots.
The pathogen belongs to the *Ascomycota* phylum, with its sexual stage being *Pyrenophora teres* (Died.) Dreyers. The conidia are pale olive in color, cylindrical, and range in size from 30–175 × 15–22.5 μm, with 1–10 septa. They are mostly produced singly but can also occur in small clusters of 2–3. The conidia are straight, with only a slight bend at the top. The ascostromata form on infected plant tissues, and the asci are dark brown, nearly elliptical, measuring approximately 430–800 × 300–600 μm. Each ascus contains 8 ascospores, sometimes 4, which are colorless, stick-shaped, and brownish-brown, with dimensions of 40–62.5 × 17.5–27.5 μm.
The disease spreads through several pathways. The primary infection sources include mycelium latent in seed coats and spores attached to the seed surface. Additionally, ascospores from diseased plant parts can infect new hosts. Seed-borne pathogens can cause seedling diseases, and spores produced on infected tissues spread via wind and rain, leading to further infections. During grain development, ascospore structures form on infected husks, and the pathogen can survive for up to seven years in the soil. Spore germination occurs optimally between 20–25°C, with 100% relative humidity significantly increasing disease incidence. Low temperatures, low light intensity, and high humidity conditions are favorable for disease development. Winter barley crops tend to experience higher disease pressure.
To manage this disease, several control methods are recommended. First, planting resistant barley varieties such as Early Maturing No. 7, Liang Erling, and Zhe Nong 8 can help reduce damage. Timely sowing is also important to avoid continuous cropping and reduce disease buildup. For chemical control, soaking seeds with a solution of TH88 (2 ml per 20 kg water) and soaking 10 kg of barley seeds for 24 hours is effective. This treatment should be done indoors or under controlled light conditions to prevent photolysis. Other seed treatments are available for managing similar diseases like barley stripe rust. In the early stages of the disease, spraying with 50% carbendazim WP diluted 800 times, 60% anti-mildew WP diluted 1000–1500 times, or 70% mancozeb WP diluted 500 times can provide good protection.