Osmanthus has high ornamental and economic value. Osmanthus leaf spot disease is a general term for various spot diseases on the leaves of osmanthus, such as brown spot, necrotic spot, and anthracnose. It causes premature leaf drop, weakens the plant's growth, affects its ornamental value, and reduces the yield of osmanthus, resulting in economic losses.

I. Osmanthus brown spot disease

1. Symptoms

Initially, affected leaves develop small, yellowish spots that fade to a pale green color. These spots gradually expand into nearly circular lesions, or, due to the restriction of leaf veins, form irregular lesions. The lesions are yellowish-brown to grayish-brown, with a yellow halo around the perimeter, and are 2-10 mm in diameter. In later stages, black mold-like substances, namely the conidia and conidiophores of the pathogen, grow on the affected areas.

2. Pathogen and pathogenesis characteristics

The pathogen causing brown spot disease in osmanthus belongs to the subphylum Deuteromycetes, class Hyphomycetes, order Moniliales, and genus Cercospora. The stroma is brown and nearly circular; conidiophores are clustered on it, pale olive-colored, unbranched, and rarely septate; conidia are obclavate, nearly colorless to pale olive-colored, straight or slightly curved, measuring 15-58 × 2.8-3.7 μm. The disease occurs from April to October, with older leaves being more severely affected than younger leaves. The pathogen overwinters as mycelium on diseased leaves, serving as the primary source of infection the following year. Under suitable temperature and humidity conditions, conidia are produced on diseased parts and transported to healthy leaves by air currents and water droplets, causing infection.

II. Osmanthus caterpillar moth

These larvae are green or yellowish-green with a white dorsal stripe. They tend to appear on the underside of leaves, feeding on the leaf tissue and leaving the bark behind. Before the larvae descend to the tree and spin their cocoons, loosen the soil around the trunk to attract them to the cocoons, then collect and destroy them. Alternatively, spray with a 500-800 times dilution of a Bt emulsion containing over 10 billion spores per ml. Another option is to spray with a 3000 times dilution of 2.5% deltamethrin EC or 20% cypermethrin EC.

III. Osmanthus leaf spot disease

1. Symptoms

The pathogen typically invades through the leaf tip and margin, initially appearing as small, light brown spots. These spots gradually enlarge into large, round or irregular lesions. In severe cases, several lesions merge to form large necrotic patches, causing up to one-third to one-half of the leaf to dry out. The lesions are grayish-brown to reddish-brown with a distinct reddish-brown edge, and sometimes curl and crack. In later stages, numerous small black dots appear on the diseased areas; these are the conidiophores of the pathogen.

2. Pathogen and pathogenesis characteristics

The pathogen causing osmanthus leaf spot disease belongs to the subphylum Deuteromycetes, class Coelomycetes, order Sphaeropodales, and genus *Leucobacter*. The conidiophores are nearly spherical with pores, 100-150 μm in diameter; the conidia are oblong to nearly fusiform, colorless, unicellular, and 6.0-9.5 × 1.8-2.5 μm in size. The pathogen develops at temperatures between 10-33℃, with an optimum of 27℃. The disease mainly occurs from July to November. The pathogen overwinters as conidiophores on diseased leaves, and conidia are spread by wind and rain. The disease is severe in hot and humid environments, poorly ventilated conditions, and when the plant is weak.

IV. Osmanthus Leaf Spot Disease

It primarily affects the leaves, initially appearing as small brown spots. These spots are round or irregular in shape, later turning gray to grayish-white in the center with reddish-brown edges, and developing a blackish-gray mold. High temperature and humidity are often predisposing factors for the disease. It spreads through wind and rain, and the disease subsides after October.

Prevention and treatment:

1. In winter, prune and remove diseased leaves and discard fallen leaves, then burn them.

2. In early May, spray with Bordeaux mixture at a ratio of 1:2:100-200. Afterward, spray with 50% benomyl at a dilution of 1000-1500 times, or methamidophos at a dilution of 500 times, or 70% thiophanate-methyl at a dilution of 1000 times.

V. Osmanthus Anthracnose

1. Symptoms

Initially, affected leaves develop small, chlorotic spots that gradually enlarge to form round, semi-circular, or oblong lesions. These lesions are light brown to grayish-white with a reddish-brown ring around the edge. Later, numerous small black dots, which are the conidiophores of the pathogen, appear on the affected areas. In humid conditions, pale pinkish-red spore clusters appear on the diseased parts.

2. Pathogen and pathogenesis characteristics

The pathogen causing anthracnose in osmanthus belongs to the subphylum Deuteromycetes, class Coelomycetes, order Colletotrichum, and genus *Anthracnose*. The conidiomata are brown or black, 100-300 μm in diameter, with several setae on them; the conidiophores are cylindrical, 12-21 × 4-51 μm in size; the conidia are cylindrical, borne under the leaf epidermis, and break through the epidermis after maturation, measuring 11-18 × 4-6 μm. The disease is most severe from April to June. The pathogen overwinters as conidiomata on diseased leaves and is spread by wind and rain.

VI. Osmanthus scale insects

In the Yangtze River basin, this pest can have 2-3 generations, with severe damage occurring from May to June and August to September. They prefer to congregate on the shady side of main shoots and in branch forks, or on branches and leaves. Both adults and nymphs secrete honeydew, leading to sooty mold on flowering plants. High temperature and humidity favor its occurrence. When only a small number occur, they can be gently brushed off with a soft brush, which is quite effective. In summer, spraying with 0.3-0.5 Baume lime-sulfur mixture or 1500 times dilution of 50% phosmet emulsifiable concentrate is beneficial, used alone or in combination, once every 7-10 days, for 2-3 consecutive applications.

7. Osmanthus Red Spider Mite

High temperature and drought conditions are common. Prevention and control methods: During dry weather, pay attention to irrigation and fertilization to promote robust plant growth and enhance insect resistance. When using chemical pesticides, it is important to rotate them frequently, as resistance can develop after the application of certain highly toxic pesticides. Spraying with a 2000-3000 times dilution of 40% cypermethrin EC or a 1500 times dilution of 40% dimethoate EC is effective.