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What are the control methods for arrowhead brown spot?

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1. Symptoms Arrowhead brown spot mainly damages leaves and leaf stalks. Leaf spots are dark brown and slightly round, later turning grayish-white in the center, with a clear boundary between diseased and healthy tissue. When the disease is severe, the spots are densely packed and merge into patches, causing the leaves to turn yellow and wither. Leaf stalk spots are nearly spindle-shaped, with the diseased area slightly sunken. When the spots expand around the stalk and merge, the leaf stalk breaks and falls over. When humid, a faintly visible thin white mold layer grows on the surface of the diseased area. 2. Transmission route and disease pattern This disease is caused by infection by the fungus Pseudocercospora sagittariae, a member of the Deuteromycotina. The pathogen overwinters as mycelium or conidiomata on corms or diseased residues,

1. Symptoms Arrowhead brown spot mainly damages leaves and leaf stalks. Leaf spots are dark brown and slightly round, later turning grayish-white in the center, with a clear boundary between diseased and healthy tissue. When the disease is severe, the spots are densely packed and merge into patches, causing the leaves to turn yellow and wither. Leaf stalk spots are nearly spindle-shaped, with the diseased area slightly sunken. When the spots expand around the stalk and merge, the leaf stalk breaks and falls over. When humid, a faintly visible thin white mold layer grows on the surface of the diseased area.

2. Transmission route and disease pattern

This disease is caused by infection by the fungus Pseudocercospora sagittariae, a member of the Deuteromycotina. The pathogen overwinters as mycelium or conidiomata on corms or diseased residues, becoming the primary infection source for the following year. During the arrowhead growing period, conidia produced on diseased areas spread through airflow and rainwater, causing repeated infections. Generally, warm and humid weather and excessive application of nitrogen fertilizer, with plants growing too densely, favor the disease.

3. Control methods

(1) Agricultural control: Breed disease-resistant varieties; strengthen fertilizer and water management, apply more organic fertilizer and phosphorus-potassium fertilizer, and avoid excessive application of nitrogen fertilizer; manage the water layer according to the growth needs of arrowhead at the germination stage, the leaf-emergence to corm-swelling stage, and the corm-formation stage, avoiding long-term deep flooding.

(2) Chemical control: Start applying chemicals in time as soon as the disease begins at the seedling stage. You can use 70% thiophanate-methyl wettable powder at 1000 times dilution plus 75% chlorothalonil wettable powder at 1000 times dilution, or 50% thiophanate-methyl and sulfur suspension concentrate, or 36% thiophanate-methyl suspension concentrate at 500-600 times dilution for spraying. To improve the spreading performance of the solution, add 0.2% laundry detergent. Spray once every 7-10 days, for 2-3 consecutive sprays.

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