The symptoms are also called spot blotch. Distributed in Shandong, Northeast China, Hebei, Xinjiang, Guizhou, Taiwan, etc. The main damage leaves. At the beginning, the veins in the beginning are polygonal or irregular to elliptic yellow-white hazel to gray-brown lesions, size 2-5mm, sometimes with brownish halos around, and late diseased parts give rise to small black spots, ie conidia of pathogens 1. When the disease is severe, the lesions merge and cause the leaves to fall early. The pathogen Septoria cannabis (Lasch.) Sacc. said hemp shell spore (Helium cannabinoidus), a subgenus fungus sporozoite conifer black, spherical, about 90 μm in diameter, scattered or aggregated on both sides of the leaf, buried Break through the skin after birth. The conidia are colorless, with needles, straight or curved, and pointed at the top, with 2-5 membranes, 3 membranes, and 45-552-2.5 (μm) in size. The optimum temperature for hypha development is 25°C, and the optimum pH is 5.2. N95 Mask,Coronavirus Mask,COVID-19 Mask,Face mask Hebei Abiding Co.Ltd , https://www.hebeiabiding.com
Transmission routes and pathogenic conditions The pathogens overwinter on contaminated bodies of contaminated or contaminated soil on the remaining surface of the ground. After the late spring and wet season, the mature conidia escaped from the orifices with a large number of conidia, which were transmitted by wind and rain. After the initial infection, the diseased department continues to produce spores for reinfection. Poorly drained wet or wet plots or partial application, over-application of nitrogen fertilizer and excessive dense planting of hemp fields are heavy.
Prevention and control methods mainly adopt agricultural technology control measures to control their damage. (1) Select high-drying plots to plant marijuana, timely drainage in the rainy season to prevent moisture retention. (2) Apply sufficient ripe organic fertilizer, increase phosphorus and potassium fertilizer, do not apply excessive nitrogen fertilizer. Properly dense planting, maintaining ventilation and light in the field, enabling healthy growth of cannabis and enhancing resistance to disease. (3) If necessary, spraying 1:20060-fold Bordeaux mixture or 14% complex ammonia bronze solution 300 times, 60% potassium copper phosphate wettable powder 500-fold solution, 50% formazan in the early stage of disease. Wettable powder 600-800 times, 50% benomyl wettable powder 1500 times.