Red Fuji apples often struggle with low sugar levels and poor coloration in the central and southern plains of Hebei. However, by implementing effective cultivation techniques, growers can significantly improve both the sweetness and appearance of the fruit. Based on our experience, here are some key practices that have proven successful:
First, ensure adequate sunlight. The light intensity within the canopy directly affects the sugar content of the fruit. Proper pruning is essential to maintain good light penetration. After winter pruning, the tree density should be kept between 7,000 to 80,000 trees per acre, and during the growing season, it should be controlled at 10,000 to 120,000 trees per acre. This helps achieve a canopy transmittance of about 25%, allowing optimal light exposure.
Second, implement rational fertilization strategies. In early autumn, apply organic manure such as human or animal waste, or cake fertilizer, making sure it is fully composted before use. During the fruit-filling stage, apply 1.5 kg of organic fertilizer per kilogram of fruit, and consider intercropping green manure crops like white clover or alfalfa to enhance soil fertility. Reduce nitrogen fertilizer use and increase phosphorus and potassium, especially in the later growth stages. This can boost the coloring index by 24.4% and sugar content by 2.4%. Foliar sprays, such as potassium fulvic acid diluted 400 times, should be applied 3–4 times during the growing season. At the time of color development, sprays like Meifeng or Qirui amino acid compound micronutrient (300 times) or Meiguoluo (600 times) can speed up coloration by 12–17 days, increase the coloring index by 24.2%, and raise sugar levels by 0.9%–1.6%. Applying boron during flowering and early fruit stages also helps improve fruit quality.
Third, use wall bees for pollination. Wall bees are highly efficient pollinators. When paired with proper pollination trees, they can result in sweeter, better-colored fruits with more uniform shape.
Fourth, manage water carefully. Excessive rainfall after September negatively impacts both sugar accumulation and color development. Avoid flooding during the late fruit-growing period, and if heavy rain occurs, drain excess water from the tree base promptly.
Fifth, choose the right rootstock. Different rootstocks affect fruit coloration significantly. For example, Gao connected to Guoguang or Marshal trees produces a coloring index of 71.1% to 76.8%, while those grafted on Golden Crown trees show lower coloration (60.3%). According to local forestry tests, M26 dwarfing rootstocks or Guoguang apple rootstocks produce well-colored fruits.
Sixth, use fruit bags. Double-layered paper bags are ideal. Bag the fruit within 35 days after flowering, remove the outer bag one week later, and take off the inner bag 20–30 days before harvest. Choose a sunny, windless day between 9:00 am and 5:00 pm for removal, and allow the inner bag to remain for 3–5 days before taking it off.
Seventh, lay reflective film under the trees. In late September, after removing the bags, place retroreflective film to enhance coloration on both the inside and underside of the canopy.
Eighth, thin leaves and rotate the fruit. Once the fruit’s sunny side begins to change color (usually 5–7 days after bag removal), gently remove shaded leaves starting from the ones closest to the fruit. Do not remove more than 30% of the total leaf area. After 10–12 days, when the fruit is fully colored, gently turn the fruit so the shaded side faces the sun, securing it with transparent tape. This should be done between noon and 4:00 pm, being careful not to damage the fruit.
Ninth, spray regularly. Spraying helps clean leaves, improve photosynthesis, reduce tree temperature, increase day-night temperature differences, and promote faster and brighter fruit coloring. Begin spraying in September, using a clean sprayer to mist leaves every evening after 5:00 pm, avoiding cloudy days.
Tenth, harvest at the right time. Fruits should be harvested in batches 20–30 days after bag removal, ideally in early November in the central and southern regions of Hebei for optimal quality.
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