In the storage of oranges, more than 20 different diseases can develop. Among these, infectious diseases are the most common, starting with Penicillium and green molds, while anthrax, peduncle rot, and black rot tend to appear in the middle and later stages. On the other hand, physiological diseases such as edema and brown spot (also known as cockroach disease) can also affect the quality of stored fruit. Based on the main diseases that occur during the storage period of citrus fruits and their patterns of development, a comprehensive approach to disease prevention and control has been developed.
One important step is pre-harvest spraying, where fungicides are applied 10 days before harvest to reduce the initial pathogen load. Commonly used options include 70% thiophanate-methyl wettable powder diluted at 1200–1500 times or 50% carbendazim wettable powder at 1000 times. Timely harvesting is also crucial—fruits should be harvested when they are about 80% mature, as harvesting too early or too late can negatively impact storage quality.
Proper picking techniques are essential to avoid damage. The "Ten Points to Note" during harvesting include avoiding harvesting in frost, dew, or rain, selecting only high-quality fruits, wearing gloves to prevent injury, and using proper cutting methods to ensure smooth removal without damaging the fruit. Fruits should be placed gently into soft baskets and kept away from damaged, fallen, sticky, or pest-infested ones.
After harvesting, it's important to treat the fruit promptly. Soaking the fruit in a solution is recommended within 24 hours. Before storage, the fruit should be pre-ventilated for 5–7 days in a well-ventilated area, extending up to 10–12 days if it rains. During this time, the fruit loses about 3–5% of its weight.
Before storing, the warehouse should be fumigated. Sulfur powder (5–10 grams per cubic meter) can be burned for 1–2 days, or formalin (30–50 ml per cubic meter) can be used for 3–4 days. The storage temperature should be between 3–4°C, with humidity maintained at 80–85%, and proper ventilation is necessary throughout.
Single fruit packaging using agricultural polyvinyl chloride film is recommended for better protection. Common preservatives include carbendazim (available in 10%, 25%, and 50% formulations), thiophanate-methyl (25%, 50%, 70%), and 2,4-D (a plant growth regulator). These preservatives help extend 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-methyl and 18–20 ml of 72% 2,4-D butyl ester. For smaller batches, 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) can be used. If 2,4-D butyl ester is unavailable, 2,4-D sodium salt dissolved in hot water can be substituted.
For wider applications, a mixture of 2.5% baking soda and 2,4-D liquid can be used. A sample formula includes 50 kg of water, 1 kg of 2.5% baking soda, and 13 ml of 72% 2,4-D butyl ester. This solution can keep the fruit fresh for up to 120 days. Another option is 25% carbendazim at 500 times plus 72% 2,4-D butyl ester at 50–100 ppm.
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