Symptom Identification and Control Methods of Camellia Anthracnose

Symptoms and pathological changes: Mainly damages leaves. Diseased leaves have round or irregular brown to grayish-brown lesions, with darker edges or yellow halos; some lesions are grayish-white, and leaf spots are sunken or have dark edges.

On the lesions, concentric-ringed or scattered small black spots appear. In humid conditions, pink gelatinous substances emerge from the small spots. Diseased leaves drop easily, and in severe cases only a few leaves remain on the whole plant; light brown spots appear on branches and twigs, which gradually dry up and turn grayish-white, with small black spots forming. In severe cases, the lesions extend downward, causing the twigs to die.

The pathogen of this disease is a fungus. The pathogen overwinters on diseased leaves and branches. When conditions are suitable, newly produced conidia and conidia that have overwintered are spread by wind, rain and insects, entering the plant through wounds, stomata or directly penetrating the epidermis. After invasion, it has a latent infection habit, and lesions appear when the plant weakens or environmental conditions favor disease development.

Control methods: 1. Strengthen fertilizer and water management, ensure nursery drainage ditches are well maintained, prevent soil from being too wet, and enhance plant disease resistance. 2. In winter, combine with pruning to remove diseased branches and leaves, clear fallen leaves, and destroy them centrally. 3. Chemical control: Spray with 25% carbendazim wettable powder at 500 times dilution, or 50% thiophanate wettable powder at 800-1000 times dilution, or 50% thiram wettable powder at 1000 times dilution. When spraying, mix in 0.3%-0.4% potassium dihydrogen phosphate solution to enhance plant resistance.

       Distribution and damage of camellia anthracnose, mainly damaging leaves and tender shoots.
 Symptoms
 Mainly damages leaves and tender shoots. The pathogen mostly invades from leaf tips and leaf margins, forming round or irregular lesions, dark brown, with raised edges, and lesions vary in size. Later, small black spots grow on the lesions, arranged in concentric rings or scattered. In high humidity, pink viscous masses overflow. Diseased leaves dry up and drop easily. Lesions on new shoots are elongated, slightly sunken, light brown, with distinct edges; in severe cases, the twigs die. 
 Occurrence pattern
 The pathogen overwinters as mycelium or acervuli on diseased plants and plant debris, and spreads through wind and rain. It mostly invades through wounds and weakened parts. Weak plant growth, poor drainage, high temperature and high humidity favor the occurrence of the disease.
 Control methods
 Clear dead branches and fallen leaves, cut off diseased branches and destroy them. Apply more organic fertilizer, phosphorus and potassium fertilizer, and ferrous sulfate to enhance disease resistance. Spray after new shoots emerge.
 Use “50% carbendazim at 800 times dilution, 70% thiophanate-methyl at 1000 times dilution, 75% chlorothalonil at 800 times dilution or 80% anthracnose thiram at 800 times dilution, once every 10-15 days, spraying 4-5 times consecutively.

Camellia Anthracnose

   [Distribution] Shanghai, Zhejiang, Yunnan, Sichuan, Guangdong, Fujian, Jiangsu, Shaanxi and other regions; it is also a serious disease on oil camellia.

   [Symptoms] Camellia anthracnose pathogen mainly infects the leaves and tender twigs of camellia. Leaf tips or leaf margins are susceptible, and it can also damage tender branches and fruits. Leaf lesions are initially light brown, semicircular or irregular, gradually turning brown; during lesion development, the color changes from inside to outside to grayish-white, with indistinct concentric wrinkles, and the edges are purplish-brown or dark brown, clearly demarcated from healthy tissue. Later, the center is grayish-white, the edges are dark brown, with concentric wrinkles, and small black spots are arranged in rings or scattered on them. Lesions vary in size and may indeed expand to the whole leaf; diseased leaves are brittle and drop easily. On fruits, lesions are purplish-brown to black, round; in severe cases, the entire fruit turns black. On tender branches, lesions are strip-shaped, purplish-brown, slightly sunken; in severe cases, the branches die. In humid environments, red mucus is easily seen on fruit lesions.
   [Pathogen]  The pathogen is a fungus, Colletotrichum camelliae. It belongs to Deuteromycotina, Coelomycetes, Melanconiales, Melanconiaceae, Colletotrichum. The pathogen infects and spreads by conidia. Conidia are borne in acervuli, long elliptical, single-celled, colorless. The temperature range for pathogen growth and development is 20-32°C, with the optimum temperature at 27-29°C.

   [Disease occurrence pattern] The pathogen overwinters as mycelium or acervuli on diseased plants or plant debris on the soil surface. When the spring temperature is above 20°C, the pathogen produces spores and spreads by wind and rain. With wind and rain, long sunny periods followed by sudden rain, or strong sun after rain, it invades leaves and tender shoots through wounds or natural openings such as leaf scars and lenticels. When tissues are tender, disease is likely to occur. Excessive nitrogen fertilizer, or barren soil with weak growth, also makes plants prone to disease. The disease period is from April to November, with the peak from June to September. Heavy clay soil, excessive nitrogen application, and tender branches and leaves favor pathogen infection. Overcrowded planting and poor ventilation favor disease spread. Generally, single-petaled camellias such as 'Jinxing' and 'Meirencha' have stronger disease resistance, while double-petaled camellias such as 'Shiba Xueshi' and 'Chang'e Fen' have weaker disease resistance.

   [Control methods]

   (1) Horticultural control: In autumn and winter, combine with pruning to remove diseased branches and clear diseased debris; in spring, promptly remove diseased leaves. When watering, pour from the edge of the pot, do not spray; use acidic mountain soil as growing medium to reduce artificial and sunscald wounds. Applying more organic fish offal fertilizer and phosphorus-potassium fertilizer can improve plant disease resistance.

  (2) Chemical control: Spray 1% Bordeaux mixture as soon as new shoots emerge to prevent initial infection. When disease occurs, spray 65% zineb at 600-800 times dilution, or 70% anthracnose thiram at 500 times dilution, or 70% mancozeb at 800 times dilution, or 75% chlorothalonil at 700 times dilution, or 50% carbendazim at 500 times dilution, repeatedly several times.