In the storage of oranges, over 20 different diseases can occur, with infectious diseases being the most common. Among these, Penicillium and green molds are the primary threats, while anthrax, peduncle rot, and black rot tend to appear in the middle and later stages. Physiological disorders such as edema and brown spot (also known as cockroach disease) also pose challenges during storage. Based on the main diseases that affect citrus fruits during this period and their occurrence patterns, an integrated approach to disease prevention and control has been developed.
1. **Pre-harvest Spraying**: To reduce the initial pathogen load, it is recommended to spray a fungicide 10 days before harvest. Options include 70% thiophanate-methyl wettable powder at a dilution of 1200–1500 times or 50% carbendazim wettable powder at 1000 times. This helps minimize the risk of infection during storage.
2. **Timely Harvesting**: Fruits should be harvested when they are about 80% mature, ensuring optimal storage potential. Harvesting too early or too late can negatively impact quality and shelf life.
3. **Proper Picking Techniques**: When harvesting citrus, follow the “Ten Rules†to protect the fruit. Avoid picking in rain, dew, or frost. Select only healthy fruits and use gloves to prevent damage. Cut the fruit carefully using a complex cutting method to avoid bruising. Place fruits in soft containers and handle them gently to avoid injury. Damaged, fallen, sticky, or infested fruits should be separated to prevent contamination.
4. **Post-harvest Treatment**: After harvesting, fruits should be treated promptly. Soaking is ideal, and the process should not exceed 24 hours. This helps in reducing microbial growth and prolongs freshness.
5. **Ventilation Pre-storage**: Before long-term storage, citrus fruits should be kept in a well-ventilated area for 5–7 days. In rainy conditions, this period may extend to 10–12 days. The moisture loss should be controlled within 3% to 5% to maintain quality.
6. **Storage Disinfection**: Before placing fruits in the storage facility, the warehouse must be fumigated. For example, 5–10 grams of sulfur powder per cubic meter can be used for 1–2 days, or 40 times diluted formalin at 30–50 ml per cubic meter, sealed for 3–4 days. Maintain a temperature between 3–4°C and humidity at 80–85%, with regular ventilation.
7. **Single-Fruit Packaging**: It is best to package each fruit individually using agricultural polyvinyl chloride film. This helps in reducing direct contact and prevents the spread of disease.
8. **Preservatives and Treatments**: Common preservatives include carbendazim (available in 10%, 25%, and 50% formulations), thiophanate (25%, 50%, 70%), and 2,4-D (a plant growth regulator). These help in extending shelf life, especially for short-term storage before the Spring Festival.
For sweet oranges, a typical formula might be: 50 kg of water mixed with 0.12 kg of 70% thiophanate and 18–20 ml of 72% 2,4-D butyl ester. If the volume is smaller, use 15 kg of water with 5 ml of 72% 2,4-D butyl ester and 0.08 kg of carbendazim (or 0.04 kg of thiophanate).
If 2,4-D butyl ester is unavailable, 2,4-D sodium salt can be used instead. Dissolve 1 g of 85% sodium salt in 80°C hot water, then mix with 4 kg of water and 5 g of 70% thiophanate (or 8 g of 25% carbendazim).
For wider applications, a solution of 2.5% baking soda mixed with 200 ppm of 2,4-D butyl ester for 5–10 minutes can be used. A formula could be 50 kg of water with 1 kg of 2.5% baking soda and 13 ml of 72% 2,4-D butyl ester. Alternatively, 25% carbendazim at 500 times dilution plus 72% 2,4-D butyl ester at 50–100 ppm can also be effective.
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