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What are the control methods for arrowhead leaf spot disease?

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1. Symptoms This disease mainly damages leaves and leaf stalks. The leaf spots are yellowish-brown to brown, polygonal, elliptical or irregular in shape, slightly zonate, surrounded by a yellow-green or green-brown halo; the spots sometimes merge with one another into large lesions, and in severe cases the leaves turn yellow and wither. On leaf stalks, the disease often produces short, streak-like brown spots, and under high humidity a gray mold grows on the surface of the spots. 2. Transmission route and disease pattern This disease is caused by infection by the fungus Cercospora sagittariae of the subphylum Deuteromycotina. The pathogen mainly overwinters as mycelium and conidiomata on diseased plant residues

1. Symptoms This disease mainly damages leaves and leaf stalks. The leaf spots are yellowish-brown to brown, polygonal, elliptical or irregular in shape, slightly zonate, surrounded by a yellow-green or green-brown halo; the spots sometimes merge with one another into large lesions, and in severe cases the leaves turn yellow and wither. On leaf stalks, the disease often produces short, streak-like brown spots, and under high humidity a gray mold grows on the surface of the spots.

2. Transmission route and disease pattern

This disease is caused by infection by the fungus Cercospora sagittariae of the subphylum Deuteromycotina. The pathogen mainly overwinters as mycelium and conidiomata on diseased plant residues. The following year it produces conidia, which are spread by airflow and wind-driven rain, causing infection; conidia are continually produced on the lesions, leading to repeated infection. High temperature and frequent rain favor the breeding and multiplication of the pathogen. The disease generally occurs readily during periods of high temperature and frequent rain in summer and autumn, and is especially severe when field ventilation is poor, fertilizer is lacking and management is neglected, or plant growth is poor.

3. Control methods

(1) Agricultural control: promptly remove diseased plant residues from the field and burn them in a centralized manner or bury them deeply; fertilize rationally, paying attention to the combined use of nitrogen, phosphorus and potassium and avoiding the one-sided application of nitrogen fertilizer; manage water scientifically, do a good job of drainage and irrigation, and improve ventilation conditions to benefit the growth of arrowhead.

(2) Chemical control: spray at the early stage of the disease, using a 600-fold dilution of 75% chlorothalonil wettable powder or a 600-fold dilution of 50% carbendazim wettable powder.

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