In the storage of citrus fruits, more than 20 diseases can occur, with infectious diseases being the most common. Among them, *Penicillium* and green molds are the primary concerns, 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. Managing citrus rot during storage and transportation is a critical issue for farmers. Based on the main diseases and their occurrence patterns, comprehensive prevention and control measures have been developed to help farmers effectively preserve mandarin oranges after harvest.
Pre-harvest spraying plays an important role in reducing disease risk. A fungicide should be applied 1–2 times approximately 10 days before harvesting. Common options include 70% thiophanate-methyl wettable powder diluted at 1200–1500 times or 50% carbendazim wettable powder at 1000 times. These treatments help reduce pathogen load on the fruit before it is picked.
Harvesting at the right time is crucial. Citrus should be harvested when the fruit reaches about 80% maturity. Harvesting too early or too late can lead to poor storage performance and increased susceptibility to disease.
Proper picking techniques are essential. Farmers should follow the “Ten Rules for Harvesting,†which include avoiding harvest during frost, dew, or rain, selecting only healthy fruits, and using gloves or cutting tools to prevent damage. Fruits should be handled gently, placed in soft containers, and sorted to separate damaged or infested fruits. Any injury or impact during handling can create entry points for pathogens.
Post-harvest treatment involves soaking the fruit in a solution for protection. The best method is to dip the fruit shortly after harvest, ideally within 24 hours. This helps prevent fungal infections and extends shelf life.
Before storage, fruits should be ventilated for 5–7 days, and up to 10–12 days if rainy. During this period, peels dry out slightly, and weight loss is typically around 3–5%.
The storage area must be disinfected before use. Sulfur fumigation at 5–10 grams per cubic meter for 1–2 days, or formalin at 30–50 ml per cubic meter for 3–4 days, is effective. Maintaining a temperature of 3–4°C and humidity between 80–85% ensures optimal conditions. Proper ventilation is also necessary to avoid moisture buildup.
Single fruit packaging using agricultural polyvinyl chloride film helps protect individual fruits from physical damage and contamination.
Preservatives like carbendazim (available in 10%, 25%, and 50% concentrations) and thiophanate-methyl (25%, 50%, 70%) are commonly used. They can be combined with plant growth regulators like 2,4-D butyl ester for better results. For example, a typical mix might include 50 kg of water with 1.2 g of 70% thiophanate-methyl and 18–20 ml of 72% 2,4-D butyl ester. If smaller quantities are needed, 15 kg of water with 5 ml of 72% 2,4-D butyl ester and 4 g of 25% carbendazim can be used.
If 2,4-D butyl ester is unavailable, 2,4-D sodium salt dissolved in hot water can be substituted. A formula could be 1 g of 85% 2,4-D sodium salt mixed with 4 kg of water and 5 g of 70% Topoxine (or 8 g of 25% carbendazim).
For thick-skinned varieties, a solution of 2.5% sodium bicarbonate (NaHCO₃) diluted 40–50 times and 200 ppm of 2,4-D can be used. This allows storage for up to 120 days. A sample formula includes 50 kg of water with 1 kg of 2.5% NaHCO₃ and 13 ml of 72% 2,4-D butyl ester.
It’s important to use the solution correctly—reconstitute when dirty and discard any unused solution after a day. These methods are widely used in regions like Yuechi County, where citrus farming is a key agricultural activity.
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