How to treat osmanthus brown spot? A detailed guide to integrated control techniques
Integrated control techniques for osmanthus brown spot
Osmanthus, an evergreen shrub or small tree of the family Oleaceae, has a straight trunk, a rounded crown, and stays green all year round, with a rich fragrance in bloom. It is a traditional garden flower and tree that we love, with unique ornamental and economic value. Osmanthus leaf spot is the general term for various spot diseases on osmanthus leaves, such as brown spot, blight spot, and anthracnose. It causes early leaf drop, weakens plant vigor, affects ornamental value, and at the same time reduces osmanthus yield, causing economic losses.
1 Osmanthus brown spot
1.1 Symptoms
On affected leaves, small chlorotic yellow spots appear at first, gradually expanding into nearly round lesions, or forming irregular lesions due to restriction by leaf veins. The lesions are yellowish brown to grayish brown, with a yellow halo around the outside, 2-10 mm in diameter. In the later stage, black mold-like growth develops on the diseased part, namely the pathogen's conidia and conidiophores.
1.2 Pathogen and disease characteristics
The pathogen of osmanthus brown spot belongs to Deuteromycotina, Hyphomycetes, Moniliales, Cercospora. The stroma is brown, nearly round; conidiophores are borne on it in bundles, pale olive, unbranched, rarely septate; conidia are obclavate, nearly colorless to pale olive, straight or slightly curved, measuring 15-58 x 2.8-3.7 μm. The disease occurs from April to October, and old leaves are more severely affected than young leaves. The fungus overwinters as mycelium on diseased leaves and serves as the primary infection source the following year. Under suitable temperature and humidity conditions, the diseased part produces conidia, which are spread by airflow and water droplets to healthy leaves, causing infection.
2 Blight spot
2.1 Symptoms
The pathogen mostly invades from the leaf tip and leaf margin. Initially there are small light brown spots, which later gradually expand into round or irregular large lesions. In severe cases, several lesions connect with each other to form large blighted spots, causing 1/3-1/2 of the whole leaf to dry up. The lesions are grayish brown to reddish brown, with a distinct reddish brown edge, sometimes curled and brittle. In the later stage, many small black dots are produced on the diseased part, namely the pathogen's pycnidia.
2.2 Pathogen and disease characteristics
The pathogen of osmanthus blight spot belongs to Deuteromycotina, Coelomycetes, Sphaeropsidales, Phyllosticta. The pycnidia are nearly spherical, with an ostiole, 100-150 μm in diameter; conidia are oblong to nearly fusiform, colorless, single-celled, measuring 6.0-9.5 x 1.8-2.5 μm. The growth temperature of the pathogen is 10-33°C, with the optimum at 27°C. The disease mostly occurs from July to November. The fungus overwinters as pycnidia on diseased leaves, and conidia are spread by wind and rain. Under high temperature and high humidity, poor ventilation, and weak plant vigor, the disease is severe.
3 Anthracnose
3.1 Symptoms
On affected leaves, small chlorotic spots appear at first, gradually expanding to form round, semicircular, or oblong lesions. The lesions are light brown to grayish white, with a reddish brown ring around the edge. In the later stage, many small black dots are produced on the diseased part, namely the pathogen's acervuli, and in humid conditions a pale pink sticky spore mass appears on the diseased part.
3.2 Pathogen and disease characteristics
The pathogen of osmanthus anthracnose belongs to Deuteromycotina, Coelomycetes, Melanconiales, Colletotrichum. The acervuli are brown or black, 100-300 μm in diameter, with several setae growing on the disc; conidiophores are cylindrical, measuring 12-21 x 4-51 μm; conidia are cylindrical, borne under the leaf epidermis and breaking through the epidermis when mature, measuring 11-18 x 4-6 μm. The disease is more severe from April to June. The fungus overwinters as acervuli on diseased leaves and is spread by wind and rain.
4 Control methods
4.1 Reduce infection sources
For potted osmanthus, diseased leaves should be removed promptly. In autumn, thoroughly clean up fallen diseased leaves and burn them in a centralized manner to reduce or eliminate the primary infection source; when nursery stock from severely affected areas leaves the nursery, soak it in a 1000-fold potassium permanganate solution for disinfection.
4.2 Landscape technical measures
Strengthen cultivation management, avoid water accumulation in the soil, apply more humus fertilizer and potassium fertilizer, plant at a reasonable density, and maintain ventilation and light transmission to improve plant disease resistance and control the occurrence of the disease.
4.3 Chemical control
Apply chemicals promptly at the early stage of the disease. For brown spot, spray with 1:2:200 lime double-strength Bordeaux mixture or 50% benomyl 1000-1500-fold solution; for blight spot, spray with 65% zineb 500-fold solution or 40% carbendazim 600-800-fold solution; for anthracnose, spray with 50% thiophanate-methyl 800-1000-fold solution or 80% anthracnose fumei 600-fold solution. The chemicals should be used alternately, with 2-3 consecutive applications for better results.
1 Osmanthus brown spot
1.1 Symptoms
On affected leaves, small chlorotic yellow spots appear at first, gradually expanding into nearly round lesions, or forming irregular lesions due to restriction by leaf veins. The lesions are yellowish brown to grayish brown, with a yellow halo around the outside, 2-10 mm in diameter. In the later stage, black mold-like growth develops on the diseased part, namely the pathogen's conidia and conidiophores.
1.2 Pathogen and disease characteristics
The pathogen of osmanthus brown spot belongs to Deuteromycotina, Hyphomycetes, Moniliales, Cercospora. The stroma is brown, nearly round; conidiophores are borne on it in bundles, pale olive, unbranched, rarely septate; conidia are obclavate, nearly colorless to pale olive, straight or slightly curved, measuring 15-58 x 2.8-3.7 μm. The disease occurs from April to October, and old leaves are more severely affected than young leaves. The fungus overwinters as mycelium on diseased leaves and serves as the primary infection source the following year. Under suitable temperature and humidity conditions, the diseased part produces conidia, which are spread by airflow and water droplets to healthy leaves, causing infection.
2 Blight spot
2.1 Symptoms
The pathogen mostly invades from the leaf tip and leaf margin. Initially there are small light brown spots, which later gradually expand into round or irregular large lesions. In severe cases, several lesions connect with each other to form large blighted spots, causing 1/3-1/2 of the whole leaf to dry up. The lesions are grayish brown to reddish brown, with a distinct reddish brown edge, sometimes curled and brittle. In the later stage, many small black dots are produced on the diseased part, namely the pathogen's pycnidia.
2.2 Pathogen and disease characteristics
The pathogen of osmanthus blight spot belongs to Deuteromycotina, Coelomycetes, Sphaeropsidales, Phyllosticta. The pycnidia are nearly spherical, with an ostiole, 100-150 μm in diameter; conidia are oblong to nearly fusiform, colorless, single-celled, measuring 6.0-9.5 x 1.8-2.5 μm. The growth temperature of the pathogen is 10-33°C, with the optimum at 27°C. The disease mostly occurs from July to November. The fungus overwinters as pycnidia on diseased leaves, and conidia are spread by wind and rain. Under high temperature and high humidity, poor ventilation, and weak plant vigor, the disease is severe.
3 Anthracnose
3.1 Symptoms
On affected leaves, small chlorotic spots appear at first, gradually expanding to form round, semicircular, or oblong lesions. The lesions are light brown to grayish white, with a reddish brown ring around the edge. In the later stage, many small black dots are produced on the diseased part, namely the pathogen's acervuli, and in humid conditions a pale pink sticky spore mass appears on the diseased part.
3.2 Pathogen and disease characteristics
The pathogen of osmanthus anthracnose belongs to Deuteromycotina, Coelomycetes, Melanconiales, Colletotrichum. The acervuli are brown or black, 100-300 μm in diameter, with several setae growing on the disc; conidiophores are cylindrical, measuring 12-21 x 4-51 μm; conidia are cylindrical, borne under the leaf epidermis and breaking through the epidermis when mature, measuring 11-18 x 4-6 μm. The disease is more severe from April to June. The fungus overwinters as acervuli on diseased leaves and is spread by wind and rain.
4 Control methods
4.1 Reduce infection sources
For potted osmanthus, diseased leaves should be removed promptly. In autumn, thoroughly clean up fallen diseased leaves and burn them in a centralized manner to reduce or eliminate the primary infection source; when nursery stock from severely affected areas leaves the nursery, soak it in a 1000-fold potassium permanganate solution for disinfection.
4.2 Landscape technical measures
Strengthen cultivation management, avoid water accumulation in the soil, apply more humus fertilizer and potassium fertilizer, plant at a reasonable density, and maintain ventilation and light transmission to improve plant disease resistance and control the occurrence of the disease.
4.3 Chemical control
Apply chemicals promptly at the early stage of the disease. For brown spot, spray with 1:2:200 lime double-strength Bordeaux mixture or 50% benomyl 1000-1500-fold solution; for blight spot, spray with 65% zineb 500-fold solution or 40% carbendazim 600-800-fold solution; for anthracnose, spray with 50% thiophanate-methyl 800-1000-fold solution or 80% anthracnose fumei 600-fold solution. The chemicals should be used alternately, with 2-3 consecutive applications for better results.