About the control technology of yellow skin anthrax
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Yellow skin anthracnose is a prevalent disease affecting the growth of yellow-skinned plants. It can affect all developmental stages, causing symptoms such as leaf spots, leaf rot, bare branches, and fruit rot, which ultimately reduce yield and fruit quality.
**Symptoms**
1. **Leaf Spot**: The lesions typically appear on both the center and edges of the leaves. They are round or semi-circular in shape, ranging from 2 to 12 mm in diameter. These spots may merge together, appearing grayish-white with a water-soaked border. The boundary between healthy and diseased tissue is clearly visible.
2. **Leaf Rot**: The infection often begins at the leaf tips or margins, leading to brown decay. The affected area expands rapidly without a clear boundary between diseased and healthy parts. Within 5 to 7 days, the entire leaf may rot. Petioles that are infected turn brown, making the leaves prone to falling early and resulting in bare branches.
3. **Shoot Wilt**: When shoots are infected, the affected areas become brown and necrotic.
4. **Fruit Rot**: Anthracnose is one of the primary causes of fruit rot. Younger fruits are more susceptible than mature ones. Initially, water-soaked brown spots appear on the fruit surface, gradually expanding into circular lesions with a brownish rot. A dense layer of orange-red viscous spores develops on the lesion's surface.
**Pathogens and Conditions**
The disease is caused by a species of *Colletotrichum* (a type of small round schizophyllan). The pathogen overwinters in the form of mycelia on infected leaves, branches, and fruits. In spring, when conditions are favorable, spores are spread by wind, rain, or insects, entering the host through wounds or stomata. The disease can occur throughout the growing season, but it is most common during the summer shoots, flowering, and fruiting stages, as well as in autumn shoots.
The optimal temperature for bacterial growth is between 21°C and 28°C, making hot and humid weather ideal for disease development. Poor cultivation practices, such as insufficient water and fertilizer, excessive use of chemical nitrogen fertilizers, or weak tree vigor, can increase the likelihood of infection. Additionally, orchard soil conditions play a role: overly heavy or loose soils with poor water retention can promote disease occurrence.
Another key factor is the latent nature of the pathogen. During typhoon seasons or heavy rains during fruit harvest, the pathogen spreads rapidly, leading to widespread fruit rot and significant losses in yield and quality.
**Control Methods**
1. **Scientific Fertilization and Irrigation**: Proper use of water and fertilizers helps strengthen the tree’s vitality and improve its resistance to diseases, reducing the risk of bacterial infections.
2. **Orchard Sanitation**: Prompt removal of infected leaves and fruits, along with proper disposal of rotten material, helps reduce the number of overwintering pathogens.
3. **Timely Pesticide Application**: Protect new shoots and young fruits by applying fungicides at the early stage of shoot growth and during fruit set. Recommended treatments include 70% Thiophanate Methyl WP diluted at 800–1000 times, 50% Tetrachloroethylene (TUF) at 500–600 times, 75% Chlorothalonil at 700–1000 times, or 50% Carbendazim WP at 500 times. Regular monitoring and timely application are essential for effective control.