Integrated control techniques of sweet-scented osmanthus brown spot

Sweet-scented osmanthus, Oleaceae evergreen shrubs or small trees, straight trunk, round crown, evergreen in four seasons, full of fragrance, are our favorite traditional garden flowers and trees, with unique ornamental value and economic value. Sweet-scented osmanthus leaf spot is the general name of all kinds of spot diseases on sweet-scented osmanthus leaves, such as brown spot, blight spot, anthracnose and so on, which cause early defoliation, weaken plant growth, affect ornamental value, reduce sweet-scented osmanthus yield and cause economic losses.

1 Brown spot of sweet-scented osmanthus

1.1 symptoms

At the initial stage of the damaged leaves, the chlorotic macula appeared, which gradually expanded into a near-round spot, or an irregular spot was formed due to the limitation of leaf veins. The lesion is yellowish brown to grayish brown with a yellow halo on the periphery, with a diameter of 2~10mm. There are black mildew in the later stage of the disease, that is, conidia and conidiophores of pathogens.

1.2 pathogen and characteristics of disease

The pathogen of sweet-scented osmanthus brown spot belongs to semi-known subphylum, Trichospora, Cercospora and Cercospora. Conidia brown, suborbicular; conidia pedicel attached to it in bundles, light olive, unbranched, rarely transverse; conidia oblong, nearly colorless to light olive, straight or slightly curved, 15-58 × 2.8-3.7 μ m in size. The disease occurred from April to October, and the disease of the old leaf was more serious than that of the young leaf. The pathogen overwintered on the diseased leaves with mycelium as the source of infection at the beginning of the next year. Under suitable conditions of temperature and humidity, conidia were produced in the diseased part, which were transmitted to healthy leaves with air flow and water droplets, causing infection.

2 blight spot

2.1 symptoms

Most of the pathogens invaded from the leaf tip and leaf margin, and at first they were small light brown spots, and then gradually expanded into large round or irregular spots. In severe cases, several disease spots connected with each other to form large withered spots, which made the whole leaf dry up to 1 inch, 1 inch, 1 inch, 2. The disease spot is grayish brown to reddish brown, the edge is bright reddish brown, sometimes curly and brittle. In the later stage, many small black dots are produced in the disease department, that is, the conidium of the pathogen.

2.2 pathogen and characteristics of the disease

The pathogen of sweet-scented osmanthus blight belongs to semi-known subphylum, Coelospora, Chlorospora, Leaf spot mold. The conidium is nearly spherical, with orifices, 100 ~ 150 μ m in diameter; the conidia are oblong to nearly fusiform, colorless, unicellular, 6.0 ~ 9.5 × 1.8 ~ 2.5 μ m in size. The development temperature of the pathogen was 10-33 ℃, and the optimum temperature was 27 ℃. Most of the diseases occurred from July to November, the pathogen overwintered on the diseased leaves with conidia, and the conidia were transmitted by wind and rain. The disease is serious in the environment of high temperature and humidity, poor ventilation and weak plant growth.

3 anthrax

3.1 symptoms

Small chlorotic spots appeared at the initial stage of the damaged leaves, which gradually expanded to form round, semicircular or oblong disease spots. The disease spot is light brown to grayish white, with reddish-brown rings on the edge. In the later stage, many small black dots were produced in the disease department, that is, the conidia disk of the pathogen, and pink myxospore clusters appeared in the disease part when it was wet.

3.2 pathogen and characteristics of the disease

The pathogen of sweet-scented osmanthus anthracnose belongs to the subphylum Cystis, Colletotrichum, Colletotrichum gloeosporioides. Conidium disk brown or black, 100 ~ 300 μ m in diameter, with several bristles on the disk; conidium cylindrical, size 12 ~ 21 × 4 ~ 51 μ m; conidium cylindrical, born under the leaf epidermis, break through the epidermis after maturity, size 11 ~ 18 × 4 ~ 6 μ m. The disease occurred seriously from April to June. The pathogen overwintered on the diseased leaves as conidia and spread by wind and rain.

4 methods of prevention and control

4.1 reduce the source of infection

The diseased leaves of potted sweet-scented osmanthus should be removed in time, and the diseased leaves should be cleaned thoroughly in autumn, so as to reduce or eliminate the source of primary infection; seedlings in severe disease areas should be soaked and disinfected with 1000 times potassium permanganate solution when they came out of the nursery.

4.2 Technical measures for gardens

Strengthen cultivation management, avoid stagnant water in soil, increase application of humus fertilizer and potassium fertilizer, reasonable close planting, maintain ventilation and light, so as to improve plant disease resistance and control the occurrence of diseases.

4.3 Chemical control

Use medicine in time at the initial stage of the disease. Brown spot can be sprayed with 1 ∶ 2 ∶ 200 times lime Bordeaux solution and 50% benzoate 1000 times solution; leaf spot can be sprayed with 65% Dysen zinc 500 times solution or 40% carbendazim 600 times solution; anthracnose can be sprayed with 50% methyl thiophanate 800 times solution or 80% anthrax Fumei 600 times solution. The medicament should be used alternately for 2 or 3 consecutive times, and the effect is better.