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Symptom identification and control methods of cotton white mildew

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Symptoms The disease occurs in the middle and late growth stages of cotton in all cotton regions. At first, white spots 3-4 mm in diameter appear between individual leaf vein networks, then become irregular polygons. On the upper surface of the leaf, the lesions are light green to yellow-green, and on the corresponding lower surface, many white frost-like conidiophores and conidia are produced. In severe cases, the diseased leaves dry up and fall off. The pathogen Ramularia areola Atk. is called white-spot Ramularia or cotton Ramularia, a fungus of the Deuteromycotina. The conidiophores are colorless, emerge in bundles from the stomata on the lower leaf surface, mostly branch at the base, and have tooth-like

Symptoms The disease occurs in the middle and late growth stages of cotton in all cotton regions. At first, white spots 3-4 mm in diameter appear between individual leaf vein networks, then become irregular polygons. On the upper surface of the leaf, the lesions are light green to yellow-green, and on the corresponding lower surface, many white frost-like conidiophores and conidia are produced. In severe cases, the diseased leaves dry up and fall off.

The pathogen Ramularia areola Atk. is called white-spot Ramularia or cotton Ramularia, a fungus of the Deuteromycotina. The conidiophores are colorless, emerge in bundles from the stomata on the lower leaf surface, mostly branch at the base, and have tooth-like protrusions at the apex with septa, measuring 23-70 x 4-6 (μm); the conidia are oblong, suddenly tapering at both ends, with 1-3 septa, measuring 14-35 x 3.5-5.0 (μm), colorless. The sexual state is Mycosphaerella areola (Atk.) Ehrl. et Wolf, called net-spored Mycosphaerella, a fungus of the Ascomycotina, and is rarely seen.

Transmission route and disease conditions The pathogen overwinters as mycelium on diseased plant residues. When conditions are suitable the following spring, conidia are produced, and the conidia spread with airflow, causing primary infection. The diseased parts then produce conidia again, continuously causing secondary infection. A temperature of 25-30°C and rainy, high-humidity conditions favor the expansion and spread of the disease.

Control methods (1) After harvest, promptly remove diseased plant residues, and bury them deeply or compost them. (2) Plant disease-resistant or disease-tolerant varieties such as BJA592, Acala1517RR, etc. (3) At the early stage of disease onset, begin spraying 50% benomyl wettable powder at 1500 times dilution or 36% thiophanate-methyl suspension at 600-700 times dilution, once every 7-10 days.

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