Occurrence and Control of Osmanthus Leaf Spot

Osmanthus fragrans, evergreen shrubs or small trees of the family Oleaceae, with straight trunks, rounded crowns, evergreens, and fragrant flowers during the flowering season, are our favorite traditional gardens and flowers, with unique ornamental and economic values. Osmanthus leaf spot disease is the general name for various spot diseases on the leaves of Osmanthus fragrans, such as brown spot, common spot disease and anthracnose, causing early defoliation, impairing plant growth, affecting ornamental value, and reducing Osmanthus production, resulting in economic losses.

1 Osmanthus brown spot

1.1 symptoms

The chlorotic yellow spots gradually appear in the affected leaves and gradually expand into near-circular lesions, or irregular lesions due to vein limitation. The lesions are yellow-brown to gray-brown with a yellow halo on the periphery and a diameter of 2-10 mm. In the later period of the disease, there were black moldy materials, namely conidia and conidiophores of pathogens.

1.2 pathogens and pathogenesis

Osmanthus brown spot pathogens belong to the semi-known fungi, subsporidia, mycetophora, stalks, and cystis. Sub-brown brown, subrounded; conidiophore stems bunched on its upper, pale olive, unbranched, rarely with transverse septa; conidiophores subulate, nearly colorless to pale olive, straight or slightly Bending, size 15 to 582.8 to 3.7 μm. Diseases occurred from April to October, and the old leaves were more severe than young leaves. The pathogens overwintered on the diseased leaf with mycelia and were the source of infestation early in the year. Under appropriate conditions of temperature and humidity, the diseased part produces conidia, which are transmitted to the healthy leaves with air currents and water droplets, causing infection.

2 dead spot

2.1 symptoms

Most of the bacteria invade from the tip of the leaf and the margin of the leaf. At the beginning, they are small spots of light brown. Later, they gradually expand into round or irregular large lesions. In severe cases, several lesions connect with each other to form large dead spots, making the whole leaf dry up to 1 /3 to 1/2. The lesions are gray-brown to reddish-brown with a sharp reddish-brown edge and sometimes crumbled. In later stages of the disease, many black dots are produced, which is the conidia of the pathogen.

2.2 pathogens and pathogenesis

Osmanthus leaf spot pathogens belong to the sub-genus, subsporidia, laminaria, sporochosporium, and genus Sp. Conidia are nearly spherical, with an orifice, diameter 100-150μm; conidia oblong to nearly fusiform, colorless, unit cell, size 6.0-9.51.8-2.5μm. Germ development temperature 10 ~ 33 °C, the optimum is 27 °C. Most of the diseases occurred in July-November. The pathogenic bacteria passed through the winter on diseased leaves, and the conidia spread by wind and rain. In severe conditions such as high temperatures and high humidity, poor ventilation, and weakened plants, the disease is severe.

3 anthrax

3.1 symptoms

In the early stages of the victim's leaves, small patches of chlorosis appeared, which gradually enlarged to form round, semicircular, or oblong lesions. The lesions are light brown to gray-white with reddish-brown edges. The late disease department produced many small black dots, namely the conidia discs of pathogenic bacteria, and the pale pink viscous spore masses appeared in the diseased part of the body.

3.2 pathogens and pathogenesis

The pathogens of sweet-scented osmanthus anthracnose belong to the sub-genus Mycobacteria, the Class of Lactobacillus, the black-sclerotium, and the genus Anthracnose. Conidia disc brown or black, diameter 100 ~ 300μm, there are several sets of bristles on the disc; conidial stem cylindrical, size 12 ~ 214 ~ 51μm; conidia cylindrical, born under the leaf epidermis, after maturation Break through the epidermis, size 11 ~ 184 ~ 6μm. The disease was severe from April to June. The pathogenic bacteria passed through the winter on the diseased leaf with conidium discs and spread by wind and rain.

4 control methods

4.1 Reduce Infection Source

Potted osmanthus should be timely removal of diseased leaves, the autumn thoroughly cleansed diseased leaves, concentrated burned to reduce or eliminate the initial infestation source; nursery outbreaks in severely afflicted areas with potassium permanganate 1000 times soaking disinfection.

4.2 Garden Technology Measures

Strengthen the cultivation and management, avoid soil water, increase the application of humus fertilizer and potash fertilizer, close-up planting, maintain ventilation and light transmission, in order to improve plant resistance to disease and control the occurrence of diseases.

4.3 Chemical control

Early onset of medication. Brown spot can be controlled by 1:2:200 times lime ratio type Bordeaux mixture, 50% Benzene 1000-1500 times spray; 65% Dyson Zinc 500 times or 40% Carbendazim 600~ 800 times liquid spray control; anthrax can be used 50% thiophanate-methyl 800 ~ 1000 times or 80% anthrax 600 times Fumei spray control. Pharmacy should be used alternately, continuous control 2 to 3 times, the effect is better.

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